Fast Twitch Formula: Unlock Your Athletic Potential with Efficient Speed Training

How can athletes improve speed and agility in just 15-25 minutes. What makes the Fast Twitch Formula suitable for busy schedules. Why does this program work for multiple sports. How does it provide instant feedback to young athletes.

Table of Contents

What is the Fast Twitch Formula and How Does it Work?

The Fast Twitch Formula is a revolutionary speed and agility training program designed to enhance athletic performance across various sports. This innovative system focuses on developing fast-twitch muscle fibers, which are crucial for explosive movements, quick acceleration, and overall speed.

Key features of the Fast Twitch Formula include:

Short, intense workouts lasting 15-25 minutes
Bodyweight exercises requiring minimal equipment
Instant feedback loop for tracking progress
Compatibility with busy schedules and other training programs
Suitability for athletes of all levels and sports

How does the Fast Twitch Formula benefit athletes?

The program offers numerous advantages for athletes looking to improve their performance:

Increased speed and agility
Enhanced power and strength
Improved footwork and coordination
Boosted confidence on the field or court
Efficient use of training time

Tailored Workouts for Maximum Efficiency

One of the standout features of the Fast Twitch Formula is its carefully crafted workout structure. The program provides every set and rep, eliminating guesswork and allowing athletes to focus solely on their performance. This meticulous approach ensures that each training session is optimized for maximum results.

How long do Fast Twitch Formula workouts take?

The workouts are designed to be completed in just 15-25 minutes, making them ideal for busy athletes. This efficient time frame allows for seamless integration into existing training schedules or packed three-sport athlete routines. The brevity of the workouts doesn’t compromise their effectiveness, as each session is carefully structured to deliver optimal results in minimal time.

Equipment-Free Training: Accessible Anytime, Anywhere

A significant advantage of the Fast Twitch Formula is its equipment-free approach. The program utilizes bodyweight exercises, eliminating the need for specialized gear or gym access. This makes it incredibly convenient for athletes to train consistently, regardless of their location or available resources.

What equipment is needed for the Fast Twitch Formula?

The only equipment required is a step or an elevated surface, which can easily be found in most households. This minimal requirement ensures that athletes can complete their workouts without any barriers, promoting consistency and adherence to the program.

Motivating Young Athletes with Instant Feedback

The Fast Twitch Formula incorporates a unique feature designed to keep young athletes engaged and motivated throughout their training journey. By implementing an instant feedback loop, similar to what one might experience in a video game, the program taps into the competitive nature of athletes.

How does the program motivate young athletes?

During each 20-30 minute training session, athletes record their scores for every exercise performed. This simple act of tracking progress introduces a competitive element, encouraging athletes to push themselves and strive for improvement. Parents and coaches often report being amazed at the newfound levels of competitiveness and dedication displayed by young athletes using this system.

Versatility for Multi-Sport Athletes

The Fast Twitch Formula is specifically designed to cater to the needs of busy, multi-sport athletes. Recognizing the demanding schedules of student-athletes, the program offers a lean and efficient approach to speed and agility training.

Can the Fast Twitch Formula be used alongside other sports commitments?

Absolutely. The program is intentionally structured to complement existing training regimens, practices, and game schedules. With workouts lasting only 20-30 minutes and recommended three times per week, athletes can easily incorporate the Fast Twitch Formula into their busy routines without overexertion or time conflicts.

Universal Application Across Sports

While speed and agility are often associated with running-based sports, the Fast Twitch Formula offers benefits that translate across a wide range of athletic disciplines.

How does speed training benefit various sports?

Speed and agility improvements extend beyond just running faster. The program enhances overall athleticism, contributing to:

Increased power generation
Improved strength and explosiveness
Enhanced on-field or on-court confidence
Better reaction times and decision-making abilities

These attributes are valuable in virtually every sport, from team-based activities like soccer and basketball to individual pursuits like tennis or martial arts.

Flexibility for Athletes of All Levels

The Fast Twitch Formula is designed to accommodate athletes at various stages of their development, from beginners to advanced competitors.

Is the program suitable for advanced athletes?

Yes, the Fast Twitch Formula is beneficial for athletes of all skill levels. The program’s exercises and intensity adapt to the individual’s current abilities. Advanced athletes will find the workouts challenging and effective in further enhancing their speed and agility. The tracking component allows seasoned competitors to measure their progress and continually push their limits.

Can beginners benefit from the Fast Twitch Formula?

Absolutely. The program’s structure makes it accessible to athletes just starting their speed and agility training journey. The bodyweight exercises and scalable intensity ensure that beginners can safely and effectively improve their athletic performance without feeling overwhelmed.

Complementing Existing Training Programs

The Fast Twitch Formula is designed to work seamlessly with other training programs and in-season commitments. This versatility makes it an excellent addition to an athlete’s overall development plan.

How can the Fast Twitch Formula be integrated with other training?

The program’s short, focused workouts can be easily incorporated into a comprehensive training regimen. Athletes can use the Fast Twitch Formula alongside:

Sport-specific skill training
Strength and conditioning programs
In-season practice and game schedules
Recovery and mobility work

This flexibility allows athletes to maintain their speed and agility development year-round without sacrificing other important aspects of their training.

Instant Access and International Availability

The Fast Twitch Formula is designed for convenience and accessibility, catering to athletes worldwide.

How is the program delivered?

The entire Fast Twitch Formula is delivered digitally, providing instant access to all workouts and resources. This digital format offers several advantages:

Immediate availability upon purchase
No shipping delays or costs
Access from any device with an internet connection
Easy updates and additions to the program

Is the Fast Twitch Formula available internationally?

Yes, due to its digital nature, the Fast Twitch Formula is available to athletes worldwide. International customers can purchase and access the program instantly, regardless of their location. This global availability ensures that athletes from all corners of the world can benefit from this cutting-edge speed and agility training system.

Risk-Free Trial with Money-Back Guarantee

To ensure customer satisfaction and confidence in the program, the Fast Twitch Formula comes with a comprehensive money-back guarantee.

What if an athlete is not satisfied with the program?

The Fast Twitch Formula offers a 60-day money-back guarantee. If at any point within the first 60 days after purchase an athlete is not satisfied with the training or doesn’t see the expected results, they can request a full refund. This risk-free trial period allows athletes to experience the benefits of the program without financial commitment.

Secure Payment Options

The Fast Twitch Formula prioritizes customer convenience and security when it comes to payment processing.

What payment methods are accepted?

The program accepts all major forms of payment, including:

Visa
Mastercard
American Express
PayPal

All transactions are processed through secure channels, ensuring that customer information is protected at all times.

Bonus Content and Additional Resources

While the Fast Twitch Formula is primarily a bodyweight-based program, it also offers additional content to enhance the training experience.

Are there any bonus materials included with the program?

Yes, the Fast Twitch Formula includes bonus training materials that incorporate resistance band exercises. These additional resources are provided at no extra cost and are designed to complement the main program. While not essential for the core Fast Twitch Formula workouts, these bonus exercises offer extra variety and challenges for athletes looking to further diversify their training.

Long-Term Access and Support

The Fast Twitch Formula is committed to supporting athletes throughout their speed and agility development journey.

How long do athletes have access to the program?

When purchased during special promotional periods, the Fast Twitch Formula often comes with lifetime access. This means that athletes can continue to use and benefit from the program indefinitely, without worrying about expiring subscriptions or limited-time access. This long-term availability allows athletes to incorporate the Fast Twitch Formula into their training regimen for years to come, adapting its use as they progress and their needs evolve.

Measurable Progress and Performance Tracking

A key feature of the Fast Twitch Formula is its emphasis on tracking and measuring progress throughout the training process.

How do athletes monitor their improvement?

The program incorporates a systematic approach to performance tracking:

Athletes record their scores for each exercise during every workout
This data allows for easy comparison of performance over time
Athletes can visually see their improvements in speed, agility, and overall performance
The tracking system provides motivation and concrete evidence of progress

This emphasis on measurable results helps athletes stay motivated and allows them to make data-driven decisions about their training focus.

Tailored Intensity for Optimal Results

The Fast Twitch Formula is designed to provide an appropriate challenge for athletes at all levels, ensuring optimal results regardless of starting point.

How does the program adapt to different skill levels?

The workouts within the Fast Twitch Formula are structured to automatically adjust to the athlete’s current abilities:

Beginners will find the exercises challenging but manageable
Intermediate athletes will experience a push in their capabilities
Advanced athletes will be tested at the upper limits of their speed and agility

This self-adjusting intensity ensures that all athletes continue to see improvements and avoid plateaus in their performance.

Comprehensive Athletic Development

While the Fast Twitch Formula primarily focuses on speed and agility, its benefits extend to overall athletic performance.

What other aspects of athleticism does the program enhance?

The Fast Twitch Formula contributes to:

Improved coordination and body control
Enhanced balance and proprioception
Increased muscular endurance
Better overall conditioning and stamina
Reduced risk of injuries through improved movement patterns

These wide-ranging benefits make the Fast Twitch Formula a valuable component of any athlete’s training regimen, regardless of their primary sport or goals.

Fast Twitch Formula

Q: Does This Program Provide Every Set And Rep?

A: Absolutely! We take all the guesswork out of the training for the Athlete so they can focus on what matters…getting better!

Q: How Long Do These Workouts Take? Will They Fit My Schedule?

They take 15-25 minutes and fit PERFECTLY with other training programs, or busy 3 Sport Athlete Schedules!

Q: Do You Need Any Equipment For The Fast Twitch Formula?

A: Nope! Everything is bodyweight! You just need a step, or something you can find around the house that is elevated.

Q: How Do I Know My Kids Will Use This Training?

A: We built these workouts to give an instant feedback loop to young Athletes (very similar to what you’d see in a Video Game). Each exercise they perform within their 20-30 minute training sessions, they will be writing down their score. Through training thousands of young Athletes, this alone brings out a different competitive edge. You will be in awe when you see your Children competing at levels you never thought they had in them.

Q: Will I Lose Access To My Account?

A: NOPE! You will receive LIFETIME ACCESS when you order during this sale!

Q: What If I Play Multiple Sports?

A: That is EXACTLY why we built this training…for “The Busy Athlete”. We know how jam packed a Student Athletes schedule is so that’s why we built the workouts to be as lean and efficient as possible. There is not a single wasted rep!

Q: Does This Work For All Sports?

A: Yes! Regardless of the Sport, Speed And Agility Matters! Speed translates to more than just running…Power, Strength, and even Confidence on the Field or Court!

Q: What If I Don’t Like The Training?

A: Do not worry! That is why we offer a 60 Day Money Back Guarantee! If at any time you are not satisfied with your order, or you do not buy into the training, then we will refund you anytime over the next 60 days!

Q: Can I mix “The Fast Twitch Formula” with other training programs or Practice and Games?

A: Absolutely! We built this Workout with exactly that in mind! We wanted to make something that A) Kids buy into that they enjoy doing and competing in. B) Something that works perfectly around their busy schedules (only 20-30 minutes 3 times per week), and C) Something that gives them instant feedback by having them track their scores on every single exercise!

Q: What If I Am More Advanced And I Already Use Weights? Is This Still For Me?

A: We created this Workout for anyone who wants to get better footwork, get quicker, and more agile with just 20-30 minutes of time. This training works perfectly in-season, or even simultaneously while training with other programs (like the 30 day TTS System for example). Every exercise is tracked and measured so as you progress through the workouts you will be able to see if you are getting quicker or not. These Workouts are also seamless to use “In Season” so you do not overdo it.

Q.Are Your Workouts Digital Or Will They Be Shipped To My House?

A.All Twice The Speed workouts are digital and you will have immediate access to them. There is NOTHING that is shipped to your house.

Q.I Am An International Customer, Can I Get These Workouts?

A.Yes, because everything is digital, you will get access to the workouts INSTANTLY!

Q: What If I Have The TTS Resistance Bands, Will I Need Those For These Workouts?

A: You will not need them for the “Fast Twitch Formula”, but we do add bonus training that include Resistance Bands exercises because we have 100,000+ Customers who have them. We are throwing them in on the house for this Special Sale!

Fast Twitch Formula — | Twice The Speed Store

Q.Do You Offer A Money Back Guarantee On Your Programs?

A.YES! All of our workouts have at least a 60 day money back guarantee!

Q.What Forms Of Payments Do You Accept?

A.We accept ALL forms of payment. Visa, Mastercard, Amex, Paypal and you information is 100% secure.

Q.I Am An International Customer, Can I Get These Workouts?

A.Yes, because everything is digital, you will get access to the workouts INSTANTLY!

Q.

Can Advanced Athletes Do These Workouts?

A.Absolutely! Our workouts will work directly with how advanced you are. The more advanced of an athlete, the harder the workouts will be (and vice versa).

Q.Can I Do Multiple Programs Together At Once?

A.Yes we actually encourage you to integrate multiple programs of ours into your weekly regimen. We do NOT recommend you do more than 3 speed training, or other high intensity training sessions per week. The other days we would recommend that you are working on your upper body strength and explosiveness.

Q.What Sport Does TTS Help The Most?

A.These workouts are built for athletes who are looking to be the fastest, and most explosive they can possibly be. You will run faster, and feel much lighter on your feet which in return will make you dominate your sport.

Q.How Old Do You Have To Be For TTS Workouts?

A.Our youngest athlete who did our program was 6 years old, and our oldest was in his mid 60’s. We show multiple levels of intensity to suit your needs.

Q.Do I Need A Weight Room?

A.Although we do recommend a weight room for more advanced athletes, our workouts can be done (and we show you) with no weights in the comfort of your own home.

Q.Are Your Workouts Digital Or Will They Be Shipped To My House?

A.All Twice The Speed workouts are digital and you will have immediate access to them. There is NOTHING that is shipped to your house.

Test Your Fast-Twitch Muscles | ACTIVE

When it comes to building a better body, every guy is looking for an edge. And while some men might opt for a ‘roid trip to an underground pharmacy, the rest of us want a safer, smarter shortcut to more muscle. And I’ve found your advantage: fast-twitch muscle training. It’s the X factor that’ll help you pack on new muscle, add strength, and even burn more fat. But before I reveal the secret, let’s make one thing clear: Nothing can help you increase the quantity of your fast-twitch fibers. That was determined at birth. This leaves you with a choice: Pray that you won the genetic lottery, or find the best way to make your fast-twitch fibers bigger. Follow this two-step approach, and you’ll build more muscle than than you ever thought possible.

Test Your Fast-Twitch Fibers

You can activate your fast-twitch fibers two ways—by lifting heavier weights or by lifting lighter weights very quickly. Take this test to determine your fast-twitch ratio. The result will tell you how you need to lift in order to see the fastest improvement.

Step 1: Test your 1-rep max on the bench press (See below). Then rest five minutes.

Step 2: Select a weight that’s 45 percent of your 1-rep max. (So if your max is 225 pounds, you’ll start with about 100 pounds.) Try to perform five reps in five seconds.

Step 3: If you succeed, rest 1 to 2 minutes and then repeat the test, this time using 5 to 10 percent more weight. Keep adding 5 to 10 percent until you can no longer complete five reps in five seconds.

Step 4: Calculate your fast-twitch ratio: Simply divide the heaviest weight you could lift in five seconds by your 1-rep max. If you lifted 135 pounds in five seconds and your max is 225, your ratio would be 60 percent.

5-rep test/1-rep max
= fast-twitch ratio

How to Test Your 1-Rep Max

Using a spotter, perform a barbell bench press. Start with half of your estimated 1-rep max, or 1RM (the amount of weight you think you can press only once). Do five or six reps with perfect technique. Now add 10 percent more weight but subtract one rep. Rest two minutes. Repeat this pattern until you do one rep with about 90 percent of your estimated 1RM. Rest three to five minutes, and try your estimated max. If you achieve it, then that’s your true 1RM. If you fail, then use the 90 percent weight; if it’s too easy, add 10 percent to your estimated 1RM.

THE WORKOUT

Now that you’ve determined your fast-twitch ratio, select one of the workouts below to do as your upper-body routine at least twice a week, making sure you never do an upper-body routine two days in a row. Alternate between exercises that share the same number (1A and 1B, for example) until you complete all exercises in the pairing. Then move on to the next exercise. Select a weight that allows you to perform at least the minimum number of reps listed.

Extraordinary fast-twitch fiber abundance in elite weightlifters

Abstract

Human skeletal muscle fibers exist across a continuum of slow → fast-twitch. The amount of each fiber type (FT) influences muscle performance but remains largely unexplored in elite athletes, particularly from strength/power sports. To address this nescience, vastus lateralis (VL) biopsies were performed on World/Olympic (female, n = 6, “WCF”) and National-caliber (female, n = 9, “NCF”; and male, n = 6, “NCM”) American weightlifters. Participant accolades included 3 Olympic Games, 19 World Championships, 25 National records, and >170 National/International medals. Samples were analyzed for myosin heavy chain (MHC) content via SDS-PAGE using two distinct techniques: single fiber (SF) distribution (%) and homogenate (HG) composition. The main finding was that these athletes displayed the highest pure MHC IIa concentrations ever reported in healthy VL (23±9% I, 5±3% I/IIa, 67±13% IIa, and 6±10% IIa/IIx), with WCF expressing a notable 71±17% (NCF = 67±8%, NCM = 63±16%). No pure MHC IIx were found with SF. Secondary analysis revealed the heavyweights accounted for 91% of the MHC IIa/IIx fibers, which caused a correlation between this FT and body mass. Additionally, when compared to SF, HG overestimated MHC I (23±9 vs. 31±9%) and IIx (0±0 vs. 3±6%) by misclassifying I/IIa fibers as I and IIa/IIx fibers as IIx, highlighting the limitation of HG as a measure of isoform distribution. These results collectively suggest that athlete caliber (World vs. National) and/or years competing in the sport determine FT% more than sex, particularly for MHC IIa. The extreme fast-twitch myofiber abundance likely explains how elite weightlifters generate high forces in rapid time-frames.

Citation: Serrano N, Colenso-Semple LM, Lazauskus KK, Siu JW, Bagley JR, Lockie RG, et al. (2019) Extraordinary fast-twitch fiber abundance in elite weightlifters. PLoS ONE 14(3):
e0207975.

https://doi.org/10.1371/journal.pone.0207975

Editor: Nir Eynon, Victoria University, AUSTRALIA

Received: November 7, 2018; Accepted: February 15, 2019; Published: March 27, 2019

Copyright: © 2019 Serrano et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript.

Funding: Funding for this project was provided by Renaissance Periodization. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Italian physician Stefano Lorenzini made the first distinction of “red” and “white” muscle fibers (myofibers) in 1678, and almost 200 years later (1873) French histologist Louis-Antoine Ranvier confirmed the existence of two distinct myofiber types in vertebrate skeletal muscle. Reintroduction of the skeletal muscle biopsy procedure in 1962 [1] allowed scientists to begin exploring the topic in athletes and resulted in the discovery that each FT is comprised of a unique MHC isoform signature. Human skeletal muscle therefore contains three pure (MHC I, IIa, and IIx) and several hybrid (single myofibers that co-expresses multiple MHC isoforms) FTs [2]. The pure and hybrid FTs combine to form a robust slow → fast continuum (MHC I → I/IIa → IIa → IIa/IIx → IIx) with each displaying specific morphological, metabolic, and contractile properties [3–6]. FT% (the relative quantity of each FT in a given muscle) influences whole muscle function [7] and is often highly correlated with athletic performance [3, 7–13].

Extensive evidence indicates endurance athletes possess a slow-twitch myofiber majority [9, 10, 12, 14, 15], yet comparatively, far few investigations have explored FT in speed, power, or strength athletes. Initial research in the 1970–80’s found that resistance-trained men expressed high quantities (~60–65%) of fast-twitch fibers [11, 12, 15, 16], which was substantiated by later studies on elite powerlifters [17] and national-caliber (‘Olympic’) weightlifters [8]. This work provided an important foundation, but used sub-elite participants [18] and/or laboratory methods that failed to accurately resolve the highly prevalent hybrids [19–21]—which compromises measurement fidelity and produces erroneous FT% conclusions [19, 22–25]. More precise techniques were developed in the early 1990’s that allowed proper quantification of FT% by analyzing each SF.

Since this time only 13 studies (Table 1) implemented SF in young speed, power, or strength-trained individuals [5, 13, 19, 20, 22, 23, 25–30], and only 3 included females (n = 13, total). Only 5/13 included athletes: unknown-caliber male sprinters (n = 6) [25], male soccer players (n = 8) [24], elite female track and field athletes from a combination of pole vault, heptathlon, 100 and 400 m hurdles, and long jump events (n = 6) [20], National-caliber male bodybuilders (n = 8) [19], and a former World-champion male sprinter (n = 1) [13]. Accurately accounting for the full FT spectrum resulted in all five studies finding far lower MHC IIa concentrations than expected (52%, 30%, 16%, 39%, and 34%, respectively). The extremely low 16% found by Parcell et al. (2003) [20] is possibly explained by sex as females are often purported to possess more slow-twitch fibers than men [31, 32]. Such sex-specific phenotypes are often the case in murine models [31], but the topic remains unexplored in athletes. Moreover, these data are difficult to interpret as the athletes sampled were from a combination of several dissimilar events.

Numerous other knowledge gaps persist because in over 50 years of human muscle FT research only two studies have utilized SF with elite (i. e., world or international) athletes (one male sprinter and six female track and field) and no research has done so with any strength or power athletes. Thus, the purpose of this study was to examine the FT% of elite weightlifters to provide novel insight into the phenotype of competitive female and male strength and power athletes.

Methods

Experimental approach to the problem

Twenty-one elite (‘Olympic’) Weightlifters (15 female, 6 male) underwent resting VL biopsies between 2–96 hours after competing in either the International Weightlifting Federation World Championships or the USA Weightlifting American Open Finals (2017). All procedures and risks were explained to the athletes prior to obtaining written consent and completing medical and exercise history questionnaires. Performance records (taken from this event) in the snatch and clean and jerk (1RM), competition medals, and other accolades were gathered from personal interviews and publically available records from these or other sanctioned meets. Each muscle sample was analyzed for MHC content using two distinct FT techniques: SF and HG. The California State University, Fullerton Institutional Review Board approved all experimental procedures prior to any testing and consent was received in oral and written format.

Participants

Participants were subdivided into three categories; WCF (n = 6 female), NCF (n = 9), and NCM (n = 6). Athletes were considered “World-caliber” if they were on the most recent Olympic or World team and competed at the most recent national event. Athletes were considered “National-caliber” if they were top 5 placers at the 2017 American Open Finals meet but had never been on a World or Olympic team. Athletes spanned multiple weight categories, had a minimum of two years of national competition experience, had competed exclusively for the United States of America, and were otherwise eligible for all American national meets (Table 2). Athlete accolades at the time of data collection included participation in 3 Olympic Games, 19 World Championships, 11 Pan American Championships, 49 National Championships, 32 American Opens, 8 University National Championships, and 25 Junior World/Pan American/National Championships. Participants also held 25 national records and >170 national/international medals either at the time of the study or in the past. One athlete had tested positive for substances prohibited by the World Anti-Doping Agency and was suspended from the sport for two years prior to participating in the study.

Procedures

Muscle biopsies.

Following 30 minutes of supine rest, athletes underwent a mid-muscle belly (approximately halfway between the greater trochanter and patella) biopsy of the VL. A detailed description of the biopsy procedure has been previously described by our lab [9, 22, 23, 33]. Briefly, a small area of the thigh was numbed by injection of a local anesthetic (Xylocaine/Lidocaine without epinephrine). An approximately ¼ inch incision was made in the superficial cutaneous tissues. Muscle samples were obtained using the Bergström technique with suction [1], immediately cleansed of excess blood and connective tissue, divided into approximately 10–15 mg strips, placed into cold skinning solution (125 mM K propionate, 2. 0 mM EGTA, 4.0 mM ATP, 1.0 mM MgCl₂, 20.0 mM imidazole [pH 7.0], and 50% [vol ml/vol ml] glycerol), and stored at -20° C for at least one week. Each sample was split such that a portion (~5 mg) could be used for SF or HG. The incision site was cleaned, pulled closed with a sterile Band-Aid, and covered with sterile gauze and cohesive bandage tape.

MHC FT identification.

All biopsy samples were analyzed for MHC via SDS-PAGE using two distinct techniques: SF and HG. For SF, individual fibers (N = 2,147; 102 ± 3 fibers per athlete) were mechanically isolated with fine tweezers under a light microscope and placed in 80 μl of sodium dodecyl sulfate (SDS) buffer (1% SDS, 23 mM EDTA, 0.008% bromophenol blue, 15% glycerol, and 715 mM b-mercaptoethanol [pH 6.8]). HG samples (~5 mg) were hand homogenized and then diluted between 1:10 to 1:50 based on sample amount and protein quantity. As described in detail elsewhere [5, 9, 22, 23, 27], 1–2 μl aliquots of both SF or HG (run separately) were then loaded into individual wells in a 3. 5% loading and 5% separating gel (SDS-PAGE), run at 5°C for 15.5 hours (SE 600 Series; Hoefer, San Francisco, CA, USA), and silver stained for MHC identification. The SF approach used known molecular weights and standards to identify the MHC isoform (MHC I, I/IIa, IIa, IIa/IIx, and IIx) of each individual myofiber. This enabled the most accurate calculation of the FT% within the muscle sample [21]. HG utilized densitometry (ImageJ, National Institutes of Health, Bethesda, MD) to quantify the relative MHC protein composition (i.e., percent area occupied by each pure isoform; MHC I, IIa, and IIx) of each sample, which is highly correlated with FT area [34]. Thus, SF indicates how frequently each isoform exists but cannot address how much area each FT occupies within the muscle. HG addresses the latter, but cannot delineate hybrids, therefore inaccurately quantifying FT% [9, 21–25, 27].

Statistical analysis

Potential differences between groups in descriptive information were examined via ANOVA. For SF, potential differences in FT% between groups were assessed via a 3 (group: WCF, NCF, NCM) x 4 (fiber type: MHC I, I/IIa, IIa, IIa/IIx) ANOVA. For HG, potential differences in FT composition between groups were examined via a 3 (group: WCF, NCF, NCM) x 3 (fiber type: MHC I, IIa, IIx) ANOVA. Comparison of SF vs. HG was accomplished by a 2 (group: SF, HG) x 3 (fiber type: MHC I, IIa, IIx) ANOVA. Effect size was calculated with Cohen’s D (0.2 = small difference, 0.5 = medium difference, and 0.8 = large difference) to identify the magnitude of difference between two groups. Pearson Product Moment Correlations (r) were assessed for WCF, NCF, and NCM between 1RM, body mass, and SF FT%. All individual FT data are reported in Table 3. Data are reported as mean ± standard deviation (SD), unless otherwise noted. Significance was established a priori at an alpha level of p < 0.05. All analyses were performed with SPSS (SPSS Statistics Version 24, IBM).

Results

Descriptive

WCF were significantly older than NCF, but not NCM (Table 2). WCF also had significantly more years of sport competition experience than NCF and NCM. NCM exceeded both WCF and NCF in relative strength in both the snatch 1RM and clean and jerk 1RM.

SF distribution

FT% for all lifters combined was 23 ± 9% I, 5 ± 3% I/IIa, 67 ± 13% IIa, and 6 ± 10% IIa/IIx. No MHC IIx or I/IIa/IIx fibers were identified. No significant differences existed between groups, despite WCF possessing 8% (absolute, not percent difference) less MHC I than NCF (d = 0.88) and NCM (d = 0.78) (Fig 1). The difference in MHC IIa between WCF and NCM (also 8%) was also not statistically significant, but had a moderate effect size (d = 0.50). The vast majority of the MHC IIa/IIx fibers (91%) belonged to just five lifters, all of whom competed in the heavyweight or super heavyweight categories (≥ 90 kg for women and ≥105 kg for men). This produced significant correlations between body mass and MHC IIa/IIx frequency for WCF (r = 0. 919, p = 0.010) and NCF (r = 0.826, p = 0.006) and a trend for NCM (r = 0.757, p = 0.080).

HG composition

FT composition for all lifters combined was 31 ± 9% I, 67 ± 9% IIa, and 3 ± 6% IIx. MHC I tended (p = 0.08) to be lower in WCF (24 ± 7%) than NCF (33 ± 9%, p = 0.125, d = 1.14) and NCM (35 ± 9%, p = 0.106, d = 1.33), yet MHC IIa was significantly higher (p = 0.046) in WCF (74 ± 6%) than NCM (61 ± 11%, p = 0.043, d = 1.39), but not NCF (65 ± 7%, p = 0.145, d = 1.28) and. FT was significantly different (p < 0.001) between SF and HG for MHC I (p = 0.005) and MHC IIx (p = 0.046), but not MHC IIa. SF MHC IIa/IIx and HG MHC IIx were highly correlated (r = 0.96, p < 0. 001). No correlations existed for SF or HG between FT% and snatch or clean and jerk relative 1RM when analyzed as subgroups or when combined together.

Discussion

The current study resulted in the most detailed investigation of muscle phenotype in Olympic and World-caliber anaerobic athletes published to date. These data are the first comparison of World vs. National-caliber athletes at the SF level. Additionally, they enabled the most precise description of FT% in strength or power sport competitors, and the first ever in females. The primary finding was that the pure MHC IIa abundance was the highest in healthy muscle (VL) ever reported, especially for females. This finding suggests athlete caliber and/or years competing in the sport influence FT% more than sex per se and also questions the pronouncement that male athletes possess more fast-twitch myofibers than females. Secondary findings revealed that our utilization of two different typing methods confirmed the limitations of HG for FT% (inappropriately categorizes MHC I/IIa as MHC I and MHC IIa/IIx as MHC IIx) and also allowed identification of a previously undocumented relationship between body mass and MHC IIa/IIx concentrations. The unique morphology and phenotypes in our participants highlight the need to further study elite anaerobic athletes, particularly females.

WCF contained the highest concentration of MHC IIa (71%) reported in the literature to our knowledge. NCF (67%) and NCM (63%) also possessed more MHC IIa than previous research in competitive male bodybuilders (40%) [16, 19] as well as male power/weightlifters [8, 11, 12, 15, 16, 18], elite female pole vaulters, heptathletes, 100 and 400 m hurdlers, and long jumpers (20), elite male hammer throwers [35], and resistance-trained men [18, 19, 22, 23, 27, 29, 36], which all ranged from 50–60%. Only six previous studies using SF have found pure MHC IIa concentrations of >50%, with just two reporting 60% (Table 1). The resulting minimal MHC I (~17–25%) in our athletes was strikingly lower than the previously described track and field athletes (57%) [20] and National-caliber bodybuilders (35%) [19]. These pronounced differences are likely explained by the substantial dissimilarities in training styles (e.g., external loading strategies, contraction type and velocity, training frequency, etc. ) between the various sports. More research is therefore needed to continue delineating the subtle but significant differences in FT% between athletes from a range of anaerobic sports and the specific role each training approach might play in altering MHC I and IIa distribution.

Although the differences in FT% between our three groups did not reach statistical significance, large effect sizes were evident and MHC IIa frequencies of 74%-89% occurred in 66% of WCF but only in 44% and 33% of NCF and NCM, respectively. Thus, scientists should further examine how FT% may separate World from National-level athletes as it would enhance our understanding of the physiological factors determining maximal human performance. For example, the only published report on a world-record holding anaerobic athlete found a FT profile remarkably different from our study or any other previous research in elite sprinters [13]. The minimal exploration in this area makes it difficult to determine if such a separation in FT profile between elite subgroups is a true and consistent phenomenon or merely an artifact of too little research.

Our groups differed in two other important characteristics; sex and years competing in the sport. Sex comparisons between athletes remain tenuous [31, 37] because nearly all investigations utilize non-gold standard FT% methods [21] and sedentary [38, 39] or “recreationally active” individuals [32]. Not only do our findings contradict the claim that women possess more slow-twitch myofibers than men [40], they illustrate the opposite when accounting for talent level (WCF < NCF = NCM). WCF had also been competing in the sport for ~5 years longer than both NCF and NCM. The current cross-sectional study-design precludes direct analysis, but extensive research affords strong support for exercise history as a critical determinate of FT% [2, 9, 26, 28, 30, 41–44]. Chronic exercise generally decreases hybrids [30, 42] and induces style-specific shifts in FT% such as increases in MHC I with endurance [9, 43, 45] or MHC IIa with sprint [28], plyometric [26], or strength training [36, 43, 44, 46]. For example, one study reported an increase in MHC IIa from 46% to 60% following 19 weeks of resistance training [36]. MHC IIa/IIx fibers appear particularly responsible for exercise-induced increases in MHC IIa and are thus uncommon in exercise-trained individuals [9, 20, 22–25, 29, 43]. A reduction of MHC IIx in favor of IIa following chronic resistance exercise is also purported extensively in the literature [28, 34], yet the overwhelming majority of this evidence comes from experiments with methodologies (e.g. HG) directly shown here and elsewhere [9, 24, 25, 47] to produce erroneous FT% conclusions.

Most research from the 1970’s– 2000’s utilized either ATPase histochemistry or HG SDS-PAGE to determine FT% [8, 14–17, 24, 25, 34, 36]. Similar to SF, histochemistry allows assessment of individual fibers for calculation of percent distribution, yet it does not enable simultaneous delineate of hybrids [36]. HG suffers the same drawback and actually indicates FT area/composition [34] more so than distribution making it greatly influenced by the size of each fiber; which is not uniform across all FTs (particularly in resistance trained individuals) [48]. All three approaches hold strong merit and are often correlated to each other [34, 49] and performance [8], but are clearly not interchangeable for maximally precise FT% assessment. In the current study, HG accurately quantified MHC IIa (within 0–4%), but not I or IIx. MHC I was overestimated by 8% percent (23 vs. 31%), which is largely explained by the non-differentiated MHC I/IIa fibers (5%). HG also greatly exaggerated MHC IIx, particularly in individuals with >4% MHC IIa/IIx. The inability of HG to account for MHC IIa/IIx explains why MHC IIx appear common in some studies [50] even though the actual abundance of pure MHC IIx fibers in healthy human skeletal muscle is extraordinarily rare; typically <0.1% [9, 22–25, 27] and 0 of the >2,100 isolated fibers from the current sample. Thus, the seeming conversion of MHC IIx to IIa with exercise is more precisely IIa/IIx changing to IIa.

MHC IIa/IIx hybrids are typically inversely associated with muscle health and physical activity [2, 9, 30, 43, 47, 51–54]. Yet, the heavyweights (male and female) expressed irregularly high concentrations (24%) and accounted for 91% of all MHC IIa/IIx myofibers, explaining the correlations between body mass and MHC IIa/IIx quantities. Terzis and colleagues (2010) noted a similar abnormal abundance of MHC IIx (typed via HG, so likely IIa/IIx) in six large (116 kg, body fat composition >22%), but presumably highly strength-trained throwers [35]. Body composition was not assessed in the current study and little research exists on well-trained, but high body mass individuals. Not knowing the amount of muscle vs. fat on these larger participants limits the ability to speculate on potential mechanisms. Thus, additional studies with a larger sample size across a broader spectrum of physical size are required to truly interpret the correlations between body mass and MHC IIa/IIx prevalence and to explore possible mechanisms.

Another juxtaposition was that of FT% and performance. Previous work in 94 kg male competitive weightlifters found strong correlations between FT composition (via HG) and the percentage of total area in a muscle that each FT occupies to both snatch 1RM and vertical jump height [8], but not clean and jerk 1RM. We failed to identify any such correlations (when all subjects were combined or sub-grouped), but also utilized multiple sexes and weight classes. Thus, while FT% differed between our groups, that factor alone did not predict performance among our lifters. Several possible explanations exist for this discrepancy. First, FT area may determine whole muscle strength more than FT%. Second, neither studies found correlations to the clean and jerk, which is heavier and slower than the snatch or vertical jump. This compliments previous isokinetic research [23] and indicates FT% does not predict performance on strength tasks among strength-trained individuals. FT% probably determines movement speed more than force production [7]. Further speculation on this point is unwarranted as limitations prohibited the ability to assess FT-specific size or contractile properties, which likely differed significantly across our groups [55] and are known to changes with training [3, 48].

Conclusion

This study provides novel insight into the muscle phenotype of elite competitive strength and power athletes and highlights the need for more research in this area. The extreme fast-twitch abundance partially explains how elite weightlifters are able to generate high forces in short time-frames. Our data also indicate that athlete caliber and years competing in the sport dictate FT% more than sex per se, but more work is needed to draw firm conclusions as a single biopsy may not perfectly represent the entire muscle [56]. Most athletes contained few hybrids and no MHC IIx or I/IIa/IIx, except the heavyweights who possessed atypically high quantities of IIa/IIx. Future research should use high fidelity techniques to explore FT-specific distribution, size, and contractile properties in female and male athletes of various caliber, sports, and body size; ideally across several years of competition. The resulting data could have practical significance if it enabled experimentation of differing training volumes or recovery protocols based on athlete-specific FT properties [57]. Scientifically, our findings importantly contribute to the knowledge-base of fiber type-specific physiology.

Acknowledgments

The authors would like to thank Irene S. Tobias and Cameron Yen for their help with this project.

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Fast Twitch Muscle Workouts – Where HIIT Meets Strength

5 hours ago “The HIIT workout was better at providing that necessary stimulus to the muscles to have a more favorable training adaptation,” lead researcher …

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The motor neurons that innervate skeletal muscle fibers are called alpha motor neurons. As the alpha motor neuron enters a muscle, it divides into several branches, each innervating a muscle fiber (note this in the image above). One alpha motor neuron along with all of the muscle fibers it innervates is a motor unit . The size of the motor unit correlates with the function of the muscle. In muscles involved with fine, coordinated control, the motor units are very small with 3-5 muscle fibers per motor neuron. Muscles that control eye movement and muscles in our hands have relatively small motor units. On the other hand in muscles involved with more powerful but less coordinated actions, like the muscles of the legs and back, the motor units are large with 1000s of muscle fibers per motor neuron.

When an action potential travels down the motor neuron, it will result in a contraction of all of the muscle fibers associated with that motor neuron. The contraction generated by a single action potential is called a muscle twitch. A single muscle twitch has three components. The latent period, or lag phase, the contraction phase, and the relaxation phase. The latent period is a short delay (1-2 msec) from the time when the action potential reaches the muscle until tension can be observed in the muscle. This is the time required for calcium to diffuse out of the SR, bind to troponin, the movement of tropomyosin off of the active sites, formation of cross bridges, and taking up any slack that may be in the muscle. The contraction phase is when the muscle is generating tension and is associated with cycling of the cross bridges, and the relaxation phase is the time for the muscle to return to its normal length. The length of the twitch varies between different muscle types and could be as short as 10 ms (milliseconds) or as long as 100 ms (more on this later).

If a muscle twitch is just a single quick contraction followed immediately by relaxation, how do we explain the smooth continued movement of our muscles when they contract and move bones through a large range of motion? The answer lies in the ordering of the firing of the motor units. If all of the motor units fired simultaneously the entire muscle would quickly contract and relax, producing a very jerky movement. Instead, when a muscle contracts, motor units fire asynchronously, that is, one contracts and then a fraction of a second later another contracts before the first has time to relax and then another fires and so on. So, instead of a quick, jerky movement the whole muscle contraction is very smooth and controlled. Even when a muscle is at rest, there is random firing of motor units. This random firing is responsible for what is known as muscle tone. So, a muscle is never “completely” relaxed, even when asleep. However, if the neuron to a muscle is cut, there will be no “muscle tone” and this is called flaccid paralysis. There are several benefits of muscle tone: First it takes up the “slack” in the muscle so that when it is asked to contract, it can immediately begin to generate tension and move the limb. If you have ever towed a car you know what happens if you don’t take the slack out of the tow rope before starting to pull. The second thing muscle tone does is deter muscle atrophy.

Muscle contractions are described based on two variables: force (tension) and length (shortening). When the tension in a muscle increases without a corresponding change in length, the contraction is called an isometric contraction (iso = same, metric=length). Isometric contractions are important in maintaining posture or stabilizing a joint. On the other hand, if the muscle length changes while muscle tension remains relatively constant, then the contraction is called an isotonic contraction (tonic = tension). Furthermore, isotonic contractions can be classified based on how the length changes. If the muscle generates tension and the entire muscle shortens than it is a concentric contraction. An example would be curling a weight from your waist to your shoulder; the bicep muscle used for this motion would undergo a concentric contraction. In contrast, when lowering the weight from the shoulder to the waist the bicep would also be generating force but the muscle would be lengthening, this is an eccentric contraction. Eccentric contractions work to decelerate the movement at the joint. Additionally, eccentric contractions can generate more force than concentric contractions. Think about the large box you take down form the top shelf of your closet. You can lower it under total control using eccentric contractions but when you try to return it to the shelf using concentric contractions you cannot generate enough force to lift it back up. Strength training, involving both concentric and eccentric contractions, appears to increase muscle strength more than just concentric contractions alone. However, eccentric contractions cause more damage (tearing) to the muscle resulting in greater muscle soreness. If you have ever run downhill in a long race and then experienced the soreness in your quadriceps muscles the next day, you know what we are talking about.

Muscle size is determined by the number and size of the myofibrils, which in turn is determined by the amount of myofilament proteins. Thus, resistance training will induce a cascade of events that result in the production of more proteins. Often this is initiated by small, micro-tears in and around the the muscle fibers. If the tearing occurs at the myofibril level the muscle will respond by increasing the amount of proteins, thus strengthening and enlarging the muscle, a phenomenon called hypertrophy. This tearing is thought to account for the muscle soreness we experience after a workout. As mentioned above, the repair of these small tears results in enlargement of the muscle fibers but it also results in an increase in the amount of connective tissue in the muscle. When a person “bulks up” from weight training, a significant percent of the increase in size of the muscle is due to increases in the amount of connective tissue. It should be pointed out that endurance training does not result in a significant increase in muscle size but increases its ability to produce ATP aerobically.

Multiple-motor unit summation or recruitment: It was mentioned earlier that all of the motor units in a muscle usually don’t fire at the same time. One way to increase the amount of force generated is to increase the number of motor units that are firing at a given time. We say that more motor units are being recruited. The greater the load we are trying to move the more motor units that are activated. However, even when generating the maximum force possible, we are only able to use about 1/3 of our total motor units at one time. Normally they will fire asynchronously in an effort to generate maximum force and prevent the muscles from becoming fatigued. As fibers begin to fatigue they are replaced by others in order to maintain the force. There are times, however, when under extreme circumstances we are able to recruit even more motor units. You have heard stories of mothers lifting cars off of their children, this may not be totally fiction. Watch the following clip to see how amazing the human body can be. Muscle recruitment. (Video Transcription Available)

Wave summation: Recall that a muscle twitch can last up to 100 ms and that an action potential lasts only 1-2 ms. Also, with the muscle twitch, there is not refractory period so it can be re-stimulated at any time. If you were to stimulate a single motor unit with progressively higher frequencies of action potentials you would observe a gradual increase in the force generated by that muscle. This phenomenon is called wave summation. Eventually the frequency of action potentials would be so high that there would be no time for the muscle to relax between the successive stimuli and it would remain totally contracted, a condition called tetanus. Essentially, with the high frequency of action potentials there isn’t time to remove calcium from the cytosol. Maximal force, then, is generated with maximum recruitment and an action potential frequency sufficient to result in tetanus.

Initial Sarcomere Length: It has been demonstrated experimentally that the starting length of the sarcomere influences the amount of force the muscle can generate. This observation has to do with the overlap of the thick and thin filaments. If the starting sarcomere length is very short, the thick filaments will already be pushing up against the Z-disc and there is no possibility for further sarcomere shortening, and the muscle will be unable to generate as much force. On the other hand, if the muscle is stretched to the point where myosin heads can no longer contact the actin, then again, less force will be generated. Maximum force is generated when the muscle is stretched to the point that allows every myosin head to contact the actin and the sarcomere has the maximum distance to shorten. In other words, the thick filaments are at the very ends of the thin filaments. These data were generated experimentally using frog muscles that were dissected out and stretched between two rods. Intact muscles in our bodies are not normally stretched very far beyond their optimal length due to the arrangement of muscle attachments and joints.

However, you can do a little experiment that will help you see how force is lost when a muscle is in a very short or a very stretched position. This experiment will use the muscles that help you pinch the pad of your thumb to the pads of your fingers. These muscles are near maximal stretch when you extend your arm and also extend your wrist. As your wrist is cocked back into maximal extension, try to pinch your thumb to your fingers. See how weak it feels? Now, gradually flex your wrist back to a straight or neutral position. You should feel your pinch get stronger. Now, flex your elbow and your wrist. With your wrist in maximal flexion, the muscles you use to pinch with are near their most shortened position. Try pinching again. It should feel weak. But, again, as you extend your wrist back to neutral you should feel your pinch get stronger.

The ultimate source of energy for muscle contraction is ATP. Recall that each cycle of a myosin head requires an ATP molecule. Multiply that by all of the myosin heads in a muscle and the number of cycles each head completes each twitch and you can start to see how much ATP is needed for muscle function. It is estimated that we burn approximately our entire body weight in ATP each day so it becomes apparent that we need to constantly replenish this important energy source. For muscle contraction, there are four ways that our muscles get the ATP required for contraction.

Cytosolic ATP: This ATP represents the “floating” pool of ATP, or that which is present and available in the cytoplasm. This ATP requires no oxygen (anaerobic) to make it (because it is already there) and is immediately available but it is short lived. It provides enough energy for a few seconds of maximal activity in the muscle-not the best source for long term contraction. Nevertheless, for the muscles of the eyes that are constantly contracting quickly but for short periods of time, this is a great source.

Creatine Phosphate: Once the cytosolic stores of ATP are depleted, the cell calls upon another rapid energy source, Creatine Phosphate. Creatine phosphate is a high energy compound that can rapidly transfer its phosphate to a molecule of ADP to quickly replenish ATP without the use of oxygen. This transfer requires the enzyme creatine kinase, an enzyme that is located on the M-line of the sarcomere. Creatine phosphate can replenish the ATP pool several times, enough to extend muscle contraction up to about 10 seconds. Creatine Phosphate is the most widely used supplement by weight lifters. Although some benefits have been demonstrated, most are very small and limited to highly selective activities.

Glycolysis: Glycolysis, as the name implies, is the breakdown of glucose. The primary source of glucose for this process is from glycogen that is stored in the muscle. Glycolysis can function in the absence of oxygen and as such, is the major source of ATP production during anaerobic activity. This series of chemical reactions will be a major focus in the next unit. Although glycolysis is very quick and can supply energy for intensive muscular activity, it can only be sustained for about a minute before the muscles begin to fatigue.

Aerobic or Oxidative Respiration: The mechanisms listed above can supply ATP for maybe a little over a minute before fatigue sets in. Obviously, we engage in muscle activity that lasts much longer than a minute (things like walking or jogging or riding a bicycle). These activities require a constant supply of ATP. When continuous supplies of ATP are required, the cells employ metabolic mechanisms housed in the mitochondria that utilize oxygen. We normally refer to these processes as aerobic metabolism or oxidative metabolism. Using these aerobic processes, the mitochondria can supply sufficient ATP to power the muscle cells for hours. The down side of aerobic metabolism is that it is slower than anaerobic mechanisms and is not fast enough for intense activity. However, for moderate levels of activity, it works great. Although glucose can also be utilized in aerobic metabolism, the nutrient of choice is fatty acids. As described below, slow-twitch and fast-twitch oxidative fibers are capable of utilizing aerobic metabolism

When we think of skeletal muscles getting tired, we often use the word fatigue, however, the physiological causes of fatigue vary considerably. At the simplest level, fatigue is used to describe a condition in which the muscle is no longer able to contract optimally. To make discussion easier, we will divide fatigue into two broad categories: Central fatigue and peripheral fatigue. Central fatigue describes the uncomfortable feelings that come from being tired, it is often called “psychological fatigue.” It has been suggested that central fatigue arises from factors released by the muscle during exercise that signal the brain to “feel” tired. Psychological fatigue precedes peripheral fatigue and occurs well before the muscle fiber can no longer contract. One of the outcomes of training is to learn how to overcome psychological fatigue. As we train we learn that those feelings are not so bad and that we can continue to perform even when it feels uncomfortable. For this reason, elite athletes hire trainers that push them and force them to move past the psychological fatigue.

Peripheral fatigue can occur anywhere between the neuromuscular junction and the contractile elements of the muscle. It can be divided into two subcategories, low frequency (marathon running) and high frequency (circuit training) fatigue. High frequency fatigue results from impaired membrane excitability as a result of imbalances of ions. Potential causes are inadequate functioning of the Na⁺/K⁺ pump, subsequent inactivation of Na⁺ channels and impairment of Ca²⁺ channels. Muscles can recover quickly, usually within 30 minutes or less, following high frequency fatigue. Low frequency fatigue is correlated with impaired Ca²⁺ release, probably due to excitation coupling contraction problems. It is much more difficult to recover from low frequency fatigue, taking from 24 hours to 72 hours.

In addition, there are many other potential fatigue contributors, these include: accumulation of inorganic phosphates, hydrogen ion accumulation and subsequent pH change, glycogen depletion, and imbalances in K⁺. Please note that factors that are not on the list are ATP and lactic acid, both of which do not contribute to fatigue. The reality is we still don’t know exactly what causes fatigue and much research is currently devoted to this topic.

Fast-twitch (type II) fibers develop tension two to three times faster than slow-twitch (type I) fibers. How fast a fiber can contract is related to how long it takes for completion of the cross-bridge cycle. This variability is due to different varieties of myosin molecules and how quickly they can hydrolyze ATP. Recall that it is the myosin head that splits ATP. Fast-twitch fibers have a more rapid ATPase (splitting of ATP into ADP + P_i) ability. Fast-twitch fibers also pump Ca²⁺ ions back into the sarcoplasmic reticulum very quickly, so these cells have much faster twitches than the slower variety. Thus, fast-twitch fibers can complete multiple contractions much more rapidly than slow-twitch fibers. For a complete list of how muscle fibers differ in their ability to resist fatigue see the table below:

	Slow Twitch Oxidative (Type I)	Fast-twitch Oxidative (Type IIA)	Fast-Twitch Glycolytic (Type IIX)
Myosin ATPase activity	slow	fast	fast
Size (diameter)	small	medium	large
Duration of contraction	long	short	short
SERCA pump activity	slow	fast	fast
Fatigue	resistant	resistant	easily fatigued
Energy utilization	aerobic/oxidative	both	anerobic/glycolytic
capillary density	high	medium	low
mitochondria	high numbers	medium numbers	low numbers
Color	red (contain myoglobin)	red (contain myoglobin)	white (no myoglobin)

In human skeletal muscles, the ratio of the various fiber types differs from muscle to muscle. For example the gastrocnemius muscle of the calf contains about half slow and half fast type fibers, while the deeper calf muscle, the soleus, is predominantly slow twitch. On the other hand the eye muscles are predominantly fast twitch. As a result, the gastrocnemius muscle is used in sprinting while the soleus muscle is important for standing. In addition, women seem to have a higher ratio of slow twitch to fast twitch compared to men. The “preferred” fiber type for sprinting athletes is the fast-twitch glycolytic, which is very fast, however, most humans have a very low percentage of these fibers, < 1%. Muscle biopsies of one world class sprinter revealed 72% fast twitch fibers and amazingly 20% were type IIX. The Holy Grail of muscle research is to determine how to change skeletal muscle fibers from one type to another. It appears that muscle fiber types are determined embryologically by the type of neuron that innervates the muscle fiber. The default muscle appears to be slow, type I fibers. If a muscle is innervated by a small neuron that muscle fiber will remain slow, whereas large mylenated fibers induce the fast isoforms. In addition, the frequency of firing rates of the neuron also alters the muscle fiber type. Research suggests that humans have subtypes of fibers, making up about <5% of the muscle, that are dually innervated and allow for switching between slow and fast to occur. Generally, it would appear that genetics determine the type of innervation that occurs and subsequent muscle fiber types and that training may be able to slightly alter the ratios due to the dually innervated muscles. However, since <5% have dual innervation, genetics is going to play a much greater role in your fiber types than your training.

Sprints and agility drills – Straight sprints can be quite boring. Try adding changes in motion to your sprint routine, such as there-backs or three-point agility drills. Sprint up and down a flight of stairs. Incorporate resistance bands or perform explosive movements underwater. You can also recruit new muscle fibers by borrowing from sports you don’t even play, but that rely on good agility, such as football, soccer, and gymnastics.
Work in some plyometrics – Plyometrics are all about quick, powerful expansions and contractions of a given muscle or muscle group. The burpee is a classic (and timeless!) example. You might also consider explosive bodyweight exercises such as jump squats, split-squat lunges, or plyo push-up. Military training and crossfit programs are famous for incorporating plyometric exercises, so start there if you need ideas.

Abbreviated multiplication formulas are used in mathematics, or rather in algebra, to quickly obtain the result of some algebraic expressions. formulas for reduced multiplication are obtained from the algebraic rules for multiplying polynomials. The use of formulas for reduced multiplication allows you to more quickly solve mathematical problems, reduce cumbersome algebraic expressions. The rules of algebra allow you to arbitrarily perform transformations of expressions using abbreviated multiplication formulas: you can represent the left side of the equality as the right side or transform the right side of the equality as the left side of the equality.It is recommended to know the abbreviated multiplication formulas by heart, since they are often used in solving problems and equations in algebra and mathematics. The most common formulas are the first three abbreviated multiplication formulas .

It is recommended to save the above figure on your computer as a cheat sheet for mathematics and algebra. The formulas shown in the figure are not a complete list of abbreviated multiplication formulas. In algebra, there are other formulas for abbreviated multiplication and division.All of these formulas have their own names. Let us consider in more detail the names of the above formulas for abbreviated multiplication.

The second [2] The formula for abbreviated multiplication is called the square of the difference. The square of the difference is the square of the first term minus twice the product of the first term and the second term of the binomial plus the square of the second term of the binomial. This formula is very similar to the formula for the square of the sum and differs only in the sign before the doubled product:

These are the three basic formulas that you need to know be sure to ! There are also formulas with cubes (see above), it is also advisable to remember them or be able to quickly deduce them. We also note that in practice we often encounter several such formulas at once in one problem – this is normal. Just get in the habit of noticing formulas and applying them carefully and you will be fine.2} {x-2y + 3} \) \ (= \)

Mathematical expressions (formulas) abbreviated multiplication
(the square of the sum and the difference, the cube of the sum and the difference, the difference of the squares, the sum and the difference of the cubes) are extremely irreplaceable in many areas of the exact sciences.These 7 symbolic notations are irreplaceable for simplifying expressions, solving equations, multiplying polynomials, canceling fractions, solving integrals and much more. This means that it will be very useful to understand how they are obtained, what they are for, and most importantly, how to remember them and then apply them. Then applying the abbreviated multiplication formula
in practice, the most difficult thing will be to see that there is x
and what do u have. Obviously no limit for a
and b
no, which means it can be any numeric or literal expressions.

The first mathematical regularity
was proved by the ancient Greek scientist Euclid, who worked in Alexandria in the 3rd century BC, he used for this a geometric method of proving the formula, since the scientists of ancient Hellas did not use letters to denote numbers.They commonly used not “a 2”, but “a square on a segment a”, not “ab”, but “a rectangle enclosed between segments a and b”.

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The use of these formulas provides a fairly quick solution to various mathematical problems, and also helps to simplify expressions. Algebraic transformation rules allow you to perform some manipulations with expressions, following which you can get the expression on the left side of the equality on the right side, or transform the right side of the equality (to get the expression on the left side after the equal sign).

The expression for the cubic difference is as follows: as the sum of the third power of the first term, triple the negative product of the square of the first term by the second, triple the product of the first term by the square of the second, and the negative cube of the second term. In the form of a mathematical expression, the cube of the difference looks like this: (a – c) ³ = a³ – 3a²c + 3ac² – c³.

It is also useful to know how to raise a binomial to a power
greater than 3.A formula for writing out the decomposition of an algebraic
sum of two terms of arbitrary degree, was first proposed by Newton in
1664–1665 and was named the Newton binomial. Odds
formulas are called binomial coefficients. If n is positive
an integer, then the coefficients vanish for any k> n,
therefore, the expansion contains only a finite number of terms. In all the rest
cases, the expansion is an infinite (binomial) series.
(The conditions for the convergence of the binomial series were first established at the beginning
19th centuryAbel.) Such special cases as