Single-leg sled pushes and pulls involve emphasizing one leg to move the sled on each step, which is especially good if you're trying to focus on a weaker side.
An easy way to implement these single-leg sled push and pull variations is to simply perform half the distance or duration with one leg and do the second half with the other leg.
The real secret to building muscle and strength is to progress. You have to challenge your body and find ways to progressively ask more of it. Christian tells you how.