Watch X-TrainFit Circuit Burnout 90 - Lower Body Circuit (2016) : Full Movie Online Free The quadriceps, booty, hamstrings, thighs and calves all get attention in this workout, while also throwing in some dynamic cardio exercises to further challenge the legs while elevating the heart rate. This workout will challenge you as you work one of the largest muscle groups in the body to tone and tighten everything below the waist.