Reverse sled drags are a great bang-for-your-buck exercise that serves as both a rehabilitative tool and a muscle/strength builder. They burn like crazy while you're doing them, but since there's no eccentric component, they don't leave you crippled with soreness so you can do them frequently, several times per week.

In this variation, row the sled toward you, then keep your elbows pulled down and back. Keep your hands pinned to your sides as you walk backwards.

Related:  9 Training Strategies for Knee Pain

Related:  Jim Wendler's Viking Day: Rope and Sled Training