Know Your Bodies’ Muscle Fibers

People wanting to improve themselves in athletics are well advised to understand the difference between the muscle fibers in their body.  By understanding the muscle fibers, and how they are affected, you can maximize your time spent in the gym by focusing on the right exercises.  The three muscle fibers in the body are:

  • Slow Twitch Fibers – “Weaker” muscle fibers.  great endurance.  used in high-endurance events like marathons.
  • Hybrid Fibers – Mix between slow twitch and fast twitch fibers.  Explosively strong and resistant to fatigue.  Infrequently found in humans.
  • Fast Twitch Fibers – Explosive, fast fibers that contract very quickly.  Tire out very quickly.

Keep in mind that fast twitch muscle fibers aren’t necessarily stronger than slow twitch.  Fast twitch fibers just contract faster, allowing for greater exertion against a weight.

There hasn’t been too many studies showing demonstrating a person changing fast twitch to slow twitch, or vice versa.  It is widely assumed your genetics plays a part in the distribution of slow twitch and fast twitch fibers throughout your body.  It has however been documented in studies that individuals can change pure fast twitch muscle fibers into the hybrid muscle fiber type.  This is often accomplished by constant endurance training combined with a weight lifting program.

That being said, hybrid muscle fibers are the best type to have for anyone wanting to increase their vertical leap, speed, strength, and endurance.  They are super fibers, in a sense; they possess the positive attributes of both slow and fast twitch fibers.  The best way to affect your muscle fiber composition is to do a routine that combines plyometrics and weight training.  These two activities will positively effect your fast twitch fibers.  The more fast twitch fibers you have, the more potential you have for the hybrid muscle fiber type.

Sprint training is the best routine there is for creating hybrid muscle fibers in your body.  Combine sprint training with weights and some endurance exercise and you will be well on your way to developing these super fibers.

Remember, in order to maximize the number of hybrid muscle fibers in your body, you must have an abundance of fast twitch fibers.  Consult the chart below for some tips on how to best train your fast twitch muscle fibers.

Table 2: The best training methods for fast-twitch motor units
Method Comments
Lifting weights in excess of 60% 1RM The heavier the weight, the greater the number and size of fast-twitch motor units recruited. A weight in excess of 75% 1RM is required to recruit the largest units
Performing a physical activity flat-out – eg sprinting, swimming, rowing or cycling as fast as possible Good recoveries are needed to maximise effort. The short-term anaerobic energy system will positively adapt. The minimum speed needed to contribute towards absolute speed development is 75% of maximum
Training your muscles eccentrically Research indicates that this form of training increases fast twitch motor unit recruitment.(6) An eccentric muscular contraction generates force when muscle fibres lengthen (see plyometric training, below)
Plyometric training These exercises utilise the stretch-reflex mechanism, allowing for much greater-than-normal force to be generated by pre-stretching a muscle (the eccentric contraction) before it contracts. A hop, bound or depth jump is an example of a plyometric conditioning drill; a long jump take-off is an example of a plyometric sport skill.
Complex training This can induce greater recruitment of fast-twitch motor units by lulling the protective mechanisms of a muscle into reduced activity, allowing it to generate greater force. Complex training involves combining weights exercises with plyometric ones in a systematic fashion (see PP 114, Feb 1999). A good example is: 1 set of 10 squats at 75% 1RM followed, after a 2-minute recovery, by 10 jump squats, repeated 3 times
Over-speed training This will have a transferable neural effect only if the athlete consciously moves his own limbs at the increased pace. It includes downhill sprinting and hitting or throwing sports using lighter implements
Good recovery 24-48 hours’ recovery should be taken between very intense plyometric/complex training and speed work sessions. A further 24-36 hours’ recovery will result in an over-compensatory peak – ie opportunity for a peak performance
Sport specific warm-up This will reduce the risk of injury, increase the receptivity of the neuromuscular system to the ensuing work and reduce the potentially contradictory effects of non-specific preparation on fast-twitch motor units
Mental preparation Maximum fast-twitch motor unit recruitment can result from specific mental preparation before and during competition


Having a specific training program designed by a professional athletic trainer with your goals in mind is paramount to making serious gains.  Train hard and train effectively to start seeing progress in your development.


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