Originally Posted by Chas Tennis
I do not know the angle of knee flexion at which the Gastrocnemius can supply little force to the Achilles Tendon. I suspect that the angle of knee flexion does not have to be very large. ?
Do you have any information on that angle?
Let me see if I understand your question. You want to essentially know that at 10 degrees of knee flexion the gastroc is producing x% of force. And at 20 degrees, etc? Is that correct?
If that is correct, then no I do not know those numbers. What you're also not considering is what the ankle is doing while the knee is being flexed.
But in the context of playing tennis, those numbers are irrelevant. Like I mentioned above, because you are requiring complex movement coupled with various degrees of explosive force, the brain's recruitment of muscles will require the whole system to be activated at some point. Even if the muscles are not actively contracting, the system will be in some state of "readiness" so to speak bc it knows that it will need to contract momentarily so it will not completely shut down.
Plus, everyone's recruitment pattern is different. Even if you knew that John's gastroc is at for example 50% activtated at 20degrees of knee flexion and 30% at 30degrees, while Phil's gastroc is 42% at 20 degrees and 25% at 30 degrees, all that goes out the window once you're on the court because John and Phil will not recruit their muscles in the same exact pattern and percentage even if you have them do the same stroke.
Bottom line, once you put a load on the system, everything changes.