go for cross trainers, you won't believe how much difference it makes. running shoes (and casual shoes) are designed to flex and facilitate a heel to toe motion. on running shoes, you often see the heel part of the outsole split in half, isolating the outside of the heel from the inside. this is because when running and walking, you strike your foot on the outside of the heel and transition to the inside of the toe for a push off (the GAIT cycle). a cross trainer will generally be lower profile, have a flatter outsole, and offer much better lateral support for weight lifting.