Jack Knife Crunch (Lv 2)

Jack Knife situps are fantastic for toning both upper and lower abdominals. Find out how many reps you should do, what muscles you’re working and how to work it into a routine @ . We offer an entire library of FREE full length home workout videos; you’ll find workouts for abdominals, lower body, Pilates, cardio, boot camp, plyometric, strength training, stretching, fat burning, tabata, sports specific, injury rehabilitation, and more. All free! Also check out