MUSCLES ENGAGED Abdominals The abdominal muscles (abs) provide movement and support to your core area. The deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will have, and this often contributes significantly to a healthy back. Equipment Used TRX Trainer Suspension training is a type of fitness training that uses a system of ropes and webbing called a "suspension trainer" and uses your own body weight as resistance. Exercise Instructions Step 1 Start in a push-up position with your hands under your shoulders, your feet in the TRX straps and one leg pulled up to your chest. Step 2 Alternate between legs and pull your knees up towards your chest. Step 3 Perform the recommended number of repetitions.