At first glance the influence of the gluteal muscles on knee health is everything but obvious. However, if you scrutinize the function of the gluteals closely, there will be a big aha-moment. In short, the gluteus maximus and posterior fibers of the gluteus medius are responsible for producing hip external rotation and abduction (moving the leg to the outside as in side-lying leg raise). Both are vital for knee health and here is why.