I'm doing a fair bit of gym and work and playing a lot of tennis so I'm not getting tired muscles when I am playing - with the exception of my right foot (I'm right handed). I've been working a lot on my footwork and trying to get my feet working more and also against the ball machine. I'm finding that my right foot seems to be getting a lot of lactic acid as if I am gripping the sole of my shoe with it. This is especially apparent if I drill open stance forehands for a long time against the ball machine. At least, it feels like lactic acid - I can't really be sure. It also hurts the next day when i get up - although whether it's the effects of the tennis or mostly plantar fasciitis I'm not exactly sure. Does anyone else experience this? What is the correct thing to be doing with your feet when actually hitting the ball? Anyway to avoid this?