Twisting the hips during squatting is a technical error that should be corrected before heavy weights are used in the exercise. Twisting not only reduces the amount of weight you can use in squats but places excessive stress on the spine.
There are many reasons such twisting can occur. The first cause of twisting during the squat -- and the one easiest to correct -- is not having your feet aligned when you squat; if your feet are not in line, your body will twist to compensate. You can have a partner check your alignment before you squat, or you can self-correct by placing a piece of athletic tape on the floor to position the tips of your toes behind.
Another issue could be tightness in the psoas (a hip flexor muscle) or an adductor (inner thigh) muscle. Stretching these muscles should help straighten you out, as will getting soft tissue treatments such as ART (Active Release Techniques®).
One common cause of twisting could be weakness in specific muscles groups. A weakness in the vastus medialis oblique, a quadriceps muscles at the bottom of the upper leg shaped like a teardrop, could cause a knee to buckle and the hips to twist. Weakness in the core muscle groups could also affect squatting alignment, and the strongman exercise called the farmer’s walk should help with this problem.
Finally, improper footwear could cause you to twist while squatting. If you wear tennis shoes, especially those that are worn more on one side, your feet may collapse which in turn rotates the knee, which in turn will rotate the hips. The best footwear to use when squatting is a weightlifting shoe because it has a sturdy base and often a cross strap for increased stability.
If you twist while you squat, try these corrective measures so you can squat strong, from start to finish.