What are the most important muscles for runners? Core Performance reports that researchers at the University of Calgary who reviewed 20 years worth of published studies found that weakness in a runner’s hip muscles significantly increase their risk of chronic knee pain, Achilles tendonitis, and pain in the sole of the foot. The researchers found that hip abductors (on the outside of your hip) are weak, knees are more likely to roll too far inward with each running stride, increasing the risk for patellofemoral pain syndrome, which causes pain under and around the kneecap; or iliotibial band syndrome, where pain arises in the outside of the knee. The good news, Core Performance reports, is that the researchers found that just six weeks of hip-muscle training can alleviate pain from various running injuries in most patients, while building up protection from future injuries. Core Performance recommends these hip strengthening moves.