hi, everyone,

I have a question about muscle recruitment.
one day, we had lab using biodex isokinetic dynamometer to get data by doing knee extension exercise. a subject performed knee extension at different velocities, three 5-reps at 90, 180 and 210 degrees/second, and last one was 20 reps at 240 degrees/second.

of course, torque and peak work decrease when velocity increases. Also, power increases when velocity increases. these relationships were obciously observed in the first three velocities. the data for the last one was showed as %fatigue, which meant performance went down by 7% in the 20 reps knee extension exercise. the subject performed his best, which meant he always extended his leg as fast as he could.

according to muscle recruitment principle, type I fiber fires when the load is light; type II and type IIb/x fiber fire in sequence when the load increases.

however, i have another thought. i would say type II fiber fires more than type I fibers in high velocity. Due to slow-twitch muscle fiber contraction speed is relatively slow, type II fiber is the major supporter to make the leg to extension at high velocity.

Generally speaking, only looking at % fatigue may not be able to decide the muscle type dominance. Endurance athletes might have lower % fatigue because their type II muscles generate less force than anaerobic athletes do. As exercise time increases, energy contribution turns to coming mainly depending on slow-twitch fiber, which is able to maintain power outcome for extended time. anaerobic athletes are supposed to have higher % fatigue. because their type II fibers are so strong, fatigue of type II fibers cause huge lose of power output.

However, by looking at only % fatigue in this lab, 20 reps might not be enough to cause much fatigue if anaerobic athletes have good muscular endurance.

My point is the firing of type II fiber is still the main factor to maintain leg extension at high velocity.

Please let me know your opinion of my thoughts. Thanks.
If any one needs further explanation of my thoughts, please let me know.