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As athletes train they are constantly thinking of new ways to build more muscle to improve their performance, but are they taking into consideration what type of muscle they should be developing? Skeletal muscle actually consist of two different types; slow twitch (ST) and fast twitch (FT). As their names suggest FT muscle fibers contract at a much faster speed (40-60 milliseconds compared to 110 milliseconds for ST), this increased speed along with their greater size allows FT muscle fibers to generate more power.
Percentage of Fast Twitch Muscle in Different People

  • Long distance runner – 25% 
  • Middle distance runner – 35% 
  • Untrained/sedentary – 45-55% 
  • Sprinter – 84% 

The fact that a sedentary or untrained individual has almost an even split between the two types shows that genetics has very little influence. Your muscle fiber composition is mostly influenced by your early sport choices and the way you train. This means as an athlete you can improve your power and speed by specializing your training to increase your FT muscle fibers.

Training to Increase Fast Twitch Muscles

Not only does training your FT muscles increase them in numbers it will also make them more efficient. Trained FT muscles remove the lactic acid (a byproduct of the anaerobic energy system) that builds up as they work, to allow the muscles to work for a longer period of time. So how can an athlete train to improve and increase their FT muscles?

  • Lifting weights in excess of 75% of your one-rep maximum (1RM) 
  • Performing a physical activity at 100% effort for under 8 seconds 
  • Eccentric muscle training (lengthening the muscle under a load) 
  • Plyometric training (increasing the amount of force generated by pre-stretching the muscle before it is contracted); hops, bounds and depth jumps are all examples 
  • Power combination training (a routine combining both heavy weight lifting and plyometrics) 

When training in such a manner it is important to allow ample time for recovery, anywhere from 24-48 hours depending on the intensity. It is also important to prepare mentally before each training session as your workout will require maximal effort at all times. It can be helpful to listen to fast paced music before and during the workout.

It is important to remember that while training with heavy weights and at a high energy level the risk of injury is significantly increased. Make sure you warm up and stretch before each exercise as well as have a cool down at the end. Always have a person to spot you when you are lifting weights that approach your 1RM. If you develop a training plan around these principals you will be able to increase your FT muscles and therefore your potential power output.

References from the SIRC Collection:

1. Carl, D. (2008). Fast Twitch/Slow Twitch Muscle Fibers. Swimming World. July 2008;49(7): 35-36. 2. Chalmers, G. R. (2008). Can fast-twitch muscle fibres be selectively recruited during lengthening contractions? Review and applications to sport movements. Sport Biomechanics, 7(1), 137-157 
3. Cunningham, P., Geary, M., Harper, R., Pendleton, A., & Stover, S. (2005). HIGH INTENSITY SPRINT TRAINING REDUCES LIPID PEROXIDATION IN FAST-TWITCH SKELETAL MUSCLE. Journal Of Exercise Physiology Online, 8(6), 18-25 
4. Maglischo, E. W. (2011). Part I: Training Fast Twitch Muscle Fibers: Why and How. Journal Of Swimming Research, 181-16. 
5. Maglischo, E. W. (2012). Part II: Training Fast Twitch Muscle Fibers: Why and How. Journal Of Swimming Research, 191-18. 
6. Quindry, J., et al (2011). Muscle-Fiber Type and Blood Oxidative Stress After Eccentric Exercise. International Journal Of Sport Nutrition & Exercise Metabolism, 21(6), 462-470. 
7. Shepherd, J. (2013). Developing A Fast Twitch Training Muscle Fiber For Speed, Power and Strength. Track Coach, (203), 6480-6482 8. Sniderman, S. (2010). Twitch-ful Thinking. Track Coach,(192) 6131-6149.

The information presented in SIRC blogs and SIRCuit articles is accurate and reliable as of the date of publication. Developments that occur after the date of publication may impact the current accuracy of the information presented in a previously published blog or article.