I was thinking about exercising and am worried too. I've read that pumping after every feeding for a bit can help. Also there are certain foods that can help you boost your supply.
I've heard is more that working out until exhausted can decrease supply, and I feel that on days I go for a run my night feeds are hurting. It could be psychosomatic right? I would stick to light weights and spot training if you are worried. Avoid exhaustion and heavy sweat.
Re: exercise and supply!