You want to milk every drop of functionality out of a shoe when you’re CrossFit training. Your shoes should help you to perform at your best, not hold you back.That means taking a few things into consideration, namely a flat heel, flexibility, and the size of the sole, as you’re ideally looking for a very thin sole to keep you as grounded as possible. If you’re planning on doing a lot of rope-climbs, you’ll also need something more durable.