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 feet in the TRX straps, your back flat and your hands placed under your shoulders. Step 2 Pull both knees into your chest and fully contract your abs. Step 3 Push your legs back to the starting position and repeat.