Originally Posted by canklecat

Yeah, foot retention is a mixed bag of good and bad. Clipless systems can strain the knee with an unnatural twisting motion. Toe clips usually lack any float so unless it's set up perfectly the position can aggravate other problems.

Personally, whenever my knee twinges and doesn't clear up quickly I switch to platform pedals and comfortable shoes for a few rides until the problem clears up. I don't see any significant difference in my average speed. The only downside to platforms for me is sometimes I get foot arch cramps from pedaling hard with shoes that have too-soft soles. I should get some Five-Tens or proper MTB shoes.