RELEVANCE OF SLOW OR FAST TWITCH MUSCLE FIBERS

Are you a runner with predominant fast-twitch muscles or slow twitch? This blog will help you get an insight into why muscle fibres vary in sportsperson and its significance.

Skeletal muscles are built by two different muscle cell types, slow-twitch or fast-twitch which is further bifurcated into intermediate fast-twitch (Type II a) and fast-twitch (Type II b)

1) Slow type (Type I) contract slowly and less forcefully. It is predominant in long-distance runners as these muscle fibres have aerobic endurance potential or in simple terms oxygen utilising capacity.

2) (a) Intermediate Fast Twitch (Type II-a)

They have tremendous aerobic potential to sustain the activity, besides, to produce more force and contraction of muscles. They can use both aerobic and anaerobic metabolism equally to create energy.

(b) Fast Twitch (Type II b)

They only limit the aerobic capacity and depict the highest contraction velocity, providing the highest force output and is required for short bursts of energy.

 Variance in  physiological characteristics

Characteristic

Type I

Type II a

Type II b

Speed of contraction

Slow

Fast

Fast

Resistance to fatigue

High

Intermediate

Low

Oxidative phosphorylation capacity

High

High

Low

 

 What Kind Of Muscle Fibres Are Recruited When And Why?

The interchange between the fibres is mainly triggered by force and fatigue. Although there is a lack of evidence, it is believed that less intense efforts like walking - slow-twitch fibres are recruited. As the efforts are increased, some of the intermediate fibres come into play. Furthermore, at half marathon pace, the maximum available slow-twitch fibres, half the available intermediate fibres and few type II be twitch fibres are recruited. Sprint requires complete recruitment of all the three fibre types.

The Variance In Physiology Of Sportsmen

The difference in aerobic and anaerobic capacity

The difference in the strength of the energy systems

The difference in the recruitment of muscle fibre

This type of training has a great influence on the muscle fibres as resistance training helps develop more of fast-twitch fibres. It depends upon whether you demand more of fast or slow-twitch muscle fibres.

In conclusion, both the muscles fibres have a different set of advantages due to variance in their characteristics. The dominate of type of muscle fibres depends upon training and type of run depending upon the distance. Further research is needed to conclude it, as the current research is limited and not conclusive.

References

Quinn, E. 2007. Fast and Slow Twitch Muscle Fibers: Does muscle type determine sports ability? Published online at About.com. (Updated October 30, 2007). Retrieved 4 March 2009 from: http://sportsmedicine.about.com/od/anatomyandphysiology/a/MuscleFiberType.htm

Magness, S. (2014). The Science of Running – How to find your limit and train to maximize your performance. Origin Publishing.

Magill, P., Schwartz, T., & Breyer, M. (2014). Build Your Running Body – A Total-Body Fitness Plan For All Distance Runners, From Milers To Ultramarathoners - Run Further, Faster, And Injury-Free. The Experiment Publishing, New York.

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