Cycling shoes are worth investing in. They're stiff, and they fit into the clips on the pedals and stay there. This allows for much greater pedaling efficiency. You can pull up on the up cycle and push down on the down cycle, allowing you to use both your quads and your hamstring. The quads tire more quickly than the hamstrings, so you want to be able to use both for pedaling, which you can do if your bike shoes are tucked tightly into the clip. Your basic cross-training or running shoe won't stay put as. Good cycling shoe brands include Avocet, Diaora and Shimano.