Fast Twitch: Part 1

What is fast twitch sports specific conditioning?  Part 1. 

Fast twitch muscles fibers are commonly known as the type of muscle fibers humans possess to perform powerful movements such as sprinting.   Fast twitch muscle fibers are developed through specific training geared to emphasize recruitment of the fast twitch muscle fibers. 

Some muscles are more heavily composed of fast twitch muscle fibers than others.   Fast twitch fibers are able to react and respond more quickly to develop tension than their counterparts.  Appropriate training methodologies will incorporate strategies to express these fibers to their maximum potential.

Muscles can be primarily defined as tonic or phasic.  Tonic muscles are considered as postural muscles and are heavily composed of slow twitch muscle fibers.  Phasic muscle, with fast twitch fibers, are utilized for larger ranges of movements and velocities.

Table 1: Characteristics of the Three Muscle Fiber Types
Fiber Type	Type IA Slow twitch oxidative	Fast Twitch Type IIA Oxidative	Fast Twitch Type II B Glycolytic
Contraction time	Slow	Fast	Very fast
Size of motor neuron	Small	Large	Very large
Resistance to fatigue	High	Intermediate	Low
Activity used for	Endurance - Light to moderate intensity steady state and interval training or activities lasting > 1min	Power Endurance – High intensity interval training or intense activities and movements sustained ranging   seconds to minutes	Power – the highest of intensity movements lasting at most several seconds
Force production	Low	High	Very high
Mitochondrial density	High	High	Low
Capillary density	High	Intermediate	Low
Oxidative capacity	High	High	Low
Glycolytic capacity	Low	High	High
Major storage fuel	Triglycerides	CP, Glycogen	CP, Glycogen

CP is creatine phosphate, Glyocgen is storage form of glucose or sugar.  Triglycerides are lipids of fats.

There are 3 identified types of muscle fibers as listed above.   Muscle fibers are often described as a certain type of twitch but muscle fibers are more accurately categorized by fuel source pathways. Therefore it is a misnomer to seek a training system that looks to recruit fast twitch muscle fibers for speed development.  Fast movements are not simply relied upon by which type of muscle fiber is being utilized.   What type of fuel that is being utilized has little impact on how fast a human can produce a movement.   Fast movements are actually more of a neurological phenomena.  Your nervous system properly recruits these muscles and also turns the right ones on at the right times.  


The ability to react is also a neurological phenomena.  Reactions under high rates of loading are even more particular of interest because of the practical need to decelerate objects, the movements of other opponents and our own bodies in sports.  Reaction to forces under high speeds require fast twitch muscle fiber recruitment and tremendous coordination of our nervous systems.  Our skin, joint, and muscle sensory receptors have to first sense the the force and quickly send a message to the brain or spinal cord.  The brain or spinal cord then propagate a message to the muscles to respond to absorb the force and even possibly create an equal or greater force against the resistance.


This all occurs in milliseconds, often with little conscious input.  If there is an alteration in our sensory perception or any delay, poor performance results and even worse, injury to our tissues may occur.  Minor impairments in these pathways are very common in athletes which results in overuse injuries.  For example, even a small percentage of poor force absorption during repetitive jumping or running will overload our ligaments, tendons and cartilage over time resulting in damage.  

The best athletes have the ability to produce coordinated movements with power and speed.  Sports training or any training should be focused on specificity.   This means in order to be as fast or powerful as possible we

• Need stability and superior control of our movement
• Must be able to progressively increase the force our muscles are able to generate
• Must progress to performing these movements as fast and powerful as possible
• Must practice doing this with movements that are specific to our sports

Training with specificity is the only way to get a desired outcome.   If a technique or method does not result in the specific enhanced attribute, such as speed, then it should be discarded.  The technique maybe a useful  activity.  However, activities such as long distance running or weight lifting are common modes used incorrectly in athletic performance programs.  If you train slow you will not get faster or more powerful.

An athlete’s performance is only improved through sports specific training.   These sport specific movements may incorporate running and resistance training but these will be performed specifically to the sport itself.   Sport specific training is setting ours goals to improve coordination, speed and power.  Running long distance and lifting weights may be very limiting aspects to focus an athlete or any human being’s training because they do not relate to most aspects of sports.  In very few sports, does it require someone to run for longer than 1 minute or press a weight into the air while lying on the back.

Training for enhanced coordination, speed, and power is improved by enhancement of the nervous system in recruiting a greater number of muscle fibers. The best athletes are able to coordinate movement patterns with a synergy not reproduced by their counterparts.  This occurs by repetitive practice with a sport specificity training style which allows for highly integrated development of the nervous and musculoskeletal system.   

Stay tuned for part II in which I will discuss and reveal how to properly train for increased speed and power.   I will also include more specific training principles and exercises.   

Thank you

Lyneil Mitchell DPT, 

A sound mind in a sound body is a short but full description of a happy state in this world - John Locke