Each runner has his or her own distinctive style of running, and there is really no single correct way of running. Still, many running experts point to poor or inefficient running form as a major cause of injury among runners. While a runner’s gait might have once been considered automatic—and therefore unchangeable—recent studies have shown positive evidence regarding the effectiveness of stride alterations in the treatment of certain running-related issues. Stride flaws result from both muscle imbalances and ingrained neuromotor patterns. Such patterns are difficult—though not impossible—to change. Common stride issues include internal rotation of the thighs upon impact (also called knock knees), overpronation of the foot, alternating hip-drop, and overstriding (i.e., pronounced heel strike). Examples of gait changes include actively and consciously engaging certain muscle groups at certain points throughout the stride, concentrating on keeping certain body parts at certain angles (e.g., keeping the knees pointed straight forward), increasing or decreasing stride length or frequency, or concentrating on maintaining proper posture. While many physical therapists believe in the use of gait retraining in response to an injury, most do not recommend it as a form of general injury prevention, as it could potentially cause a different injury.