Suspension Trainer knee tucks

This exercise provides the benefits of both a plank and a crunch. 
Adjust the TRX Suspension Trainer cables so they hang about 12 inches off the ground. -

Place your feet in the foot cradles, with the tops of your feet facing the ground. Point your toes down toward the floor. Reach your arms out and get into push-up position. -

Pull your knees into your chest as you bring your hips up slightly into the air. Extend the legs and return to the starting position. Complete the appropriate number of repetitions.