Holding Your Body Up & Lifting Your Legs Up & Down During Stomach Crunches. Part of the series: Gym Slim. Holding your body up and lifting your legs up and down during stomach crunches is a really great way to work out a few different parts of your body simultaneously. Learn all about the technique of holding your body up and lifting your legs up and down during stomach crunches with help from a certified personal trainer in this free video clip.