There are many ways you can use the TRX system, but each relies on your body weight and gravity to give you a challenging workout without free weights. The TRX strap adds an element of instability to familiar exercises like push-ups, planks, bicep curls, and squats. By holding the handles or inserting your feet through the foot cradles, the strap forces you to engage more muscle groups at once. Over time, this builds strength and improves balance.