This is another one of those exercises we did in high school gym class.
It’s great for your legs and puts a hurting on your arms too.
Start out on your hands and knees, then come onto your hands and feet. Put one leg forward underneath your chest and have the other straight back behind you.
To do the exercise, keep alternating legs back and forth. It’s like your legs are running, but since your hands are on the ground, it’s like climbing a flat mountain! 🙂