How to do Single Leg Wall Sit. You can progress to a single-leg wall sit, which will challenge your balance and work more muscles. Once you are in the standard wall sit position, extend one leg out in front of you at a time in an alternating fashion from left to right, shifting the load onto your stabilizing leg. From the wall sit position, extend one leg in front of you for a few seconds. Single-Leg Wall Sit. Be sure your thighs remain parallel to the floor and your knees are directly over your ankles. Once you're in your wall sit, spread both arms out beside you with your palms touching the wall to help keep your balance. Wall Sit Test 2. Validity, Reliability, Objectivity Factors Validity: The tests were extremely valid in assessing the muscular endurance of the upper leg, Return that leg to the floor and then extend the other leg. Purpose: The purpose of the wall sit test is to measure the strength endurance of the lower body, particularly the quadriceps muscle group. Single-Leg Wall Sit. For an even bigger burn in your legs, try these five super tough wall-sit variations. But before you do, make sure that you've mastered the standard wall sit first. 3.