Hypertrophy
Muscle cell damage after eccentric exercise is observed to occur in fast-twitch fibres. Studies have shown that the thickness of the Z-line is significantly less in IIA and IIB fibres than in I fibres.
IIB (Fast-twitch Glycolytic) = 60nm
IIA (Fast-twitch Oxidative Glycolytic) = 80nm
I (Slow-twitch Oxidative) = 150nm
The Z-line adheres to the sarcolemma to give stability to the contractile structure and has been identified as the weak link in eccentric contraction induced muscle injury.
It has been suggested by Albert that because II fibres are not always required for concentric and isometric muscle activity (remember they feature heavily in eccentric muscle activity), then the II fibres may become relatively untrained due to lack of training, and that this may predispose them to injury.
Theories on Training
Muscles that have a predominance of Fast-twitch fibres should respond to:
a lower volume and/or frequency of training
lower repetition ranges and/or shorter time under tension
longer recovery periods
Muscles that have a predominance of Slow-twitch fibres should respond to:
higher volume and/or frequency of exercise
higher repetition ranges and/or longer time under tension
shorter recover periods
The intermediate fibres fall in between these two types. For each exercise, there may be an optimal time under tension whereby your muscles receive maximal growth stimulation.
"We now believe that the concept of double progression (increasing weight and reps) is actually mistaken. Instead,