Originally Posted by RogueFLIP
Both muscles are working during tennis.
The gastroc tends to be the primary plantarflexor of the ankle while the soleus is considered secondary. However the body will recruit every muscle possible during athletic movement in order to do what the mind wants to do.
"The gastroc tends to be the primary plantarflexor of the ankle" - that depends largely on the angle of the knee joint.
I believe for the most of the time during tennis play the knee is bent. Do we agree that the Soleus is then involved but that the Gastrocnemius is not? (Since the Gastrocnemius attaches above the knee it goes slack as the knee becomes bent.)
I can see that even if the Soleus is active much more of the time, the Gastrocnemius could receive excessive stress briefly. For example, if the player runs full to the side and, to stop, puts out a straight turned back leg that stretches the calf then that could stretch and stress the Gastrocnemius.