We may be running on two legs but each take turns hitting the ground. We need to train them to maintain strength and stability throughout the running motion. This will help in improving endurance and injury resistance.
A single-leg squat is perfect for this but doing a regular one is extremely challenging for all but the highly conditioned athletes. Making it a TRX workout makes it more accessible since people can use the straps for support and balance. They are more likely to complete the full range of motion without falling down.
To do this workout, stand facing the anchor point with arms in front grabbing the handles. Let one foot stay on the ground while you lift the other. Lower your tailbone slowly while keeping the straps taut until both your upper legs are parallel to the ground.
Lift yourself up by putting your weight on your heel until you are back standing upright. Do the same for the other leg.