#WHWeekendChallenge : Reverse Lunge and Rotate. This exercise is super efficient. It taps into the deep abdominal muscles—the transverse abdominis—that pull in your waistline like a corset, and it also works your hip flexors and hamstrings, tightening your butt and thighs. Try doing 3 sets of 10 reps on each side. SO...ARE YOU IN?