In athletic development, it is valuable to understand the qualities of fast-twitch vs. slow-twitch muscles fibers
In most sports, based on the energy systems used, having a higher ratio of fast-twitch to slow-twitch is most likely beneficial, however both play an important role
Slow-twitch fibers are known as:
-Type I (slow, fatigue-resistant) muscle fibers
Fast-twitch fibers are broken up into 2 types:
-Type IIA (fast, moderately fatigable) muscle fibers
-Type IIB (very fast, highly fatigable) muscle fibers
Fast-twitch fibers have the ability to produce force & relax at a faster rate than slow twitch fibers
Fast-twitch fibers also have a higher maximum contraction velocity
-Fast-twitch: ~10 optimal fiber lengths per second
-Slow-twitch: ~3 optimal fiber lengths per second
In terms of energy systems, the difference in fiber type also come from the ability to produce ATP
-Fast twitch fibers create ATP anaerobically (without oxygen) making them fatigue easier
-Slow twitch fibers create ATP aerobically (with oxygen) making them resistant to fatigue
In humans, all of our muscles contain a combination of both fiber types with one type being dominant in each muscle. The easiest way to understand this concept is by looking at the muscles of the calf: the gastrocnemius & soleus
The gastrocnemius mainly contains fast-twitch fibers so it is useful during movements that require a large production of force at a fast rate
The soleus mainly contains slow-twitch fibers and is useful during movements that last a longer period of time
In terms of development, we must understand the Henneman’s size principle- smaller units are recruited by CNS before larger motor units. The smallest motor units contain Type I fibers. Slightly larger motor units contain type IIA and the largest motor units contain type IIB fiber
This means for kids to develop the type II muscle fibers necessary to play sport they must be doing movement that produce high force at fast rates like sprinting & jumping. As they get older and physically develop, additional training modalities can be added
e.g. weightlifting
Comments