Squat safety - Training Tips - Cover Story

American Fitness, Nov-Dec, 2001 by Jeff Chandler, Ben Kibler, Jim McMillan, David Richards

The squat is typically a barbell exercise in which the individual starts in a standing position with the barbell on the back and bends the knees to squat down until the thighs are parallel to the floor. It has been the subject of some controversy in exercise prescription, primarily because of the belief that it causes knee and/or low back pain or injury. However, when examining the safety of the squat, it is appropriate to review the history, science and practical application of this activity.

Any resistance exercise performed improperly can result in injury. Such injury can occur due to overtraining and excessive resistance or use of improper form in performing the exercise. Thus, exercise technique is paramount.

Historical Perspective

In the 1960s, scientific research indicated that squatting movements could be detrimental to the knees. Even when properly executed, the squat exercise reportedly stretched the knee ligaments in both medial/lateral and posterior/anterior directions. Possible flaws regarding this research include choice of subjects and investigators' bias. For example, parachute jumpers were used as subjects in one of the studies. Medial/lateral knee ligament injuries are common in this group because the legs are often caught in parachute lines as the canvas opens. Also, parachutists place excessive force on the knee joint when landing.

Recent Scientific Evidence

Since work conducted in the 1960s, several research studies have expanded our knowledge and understanding of knee injuries. These include studies of athletes, animals and individuals who have been through injury rehabilitation. One study used an instrument to measure anterior/posterior displacement of the tibia relative to the femur. Subjects performed varying depths of squats over an eight-week period. Additional data was collected on groups of weightlifters, powerlifters and age-matched controls. Over the eight-week period, there was no increased instability created relative to squat depth. Therefore, according to this study, squats do not negatively affect knee stability.

Using the same instrument, another group of researchers determined that acute bouts of exercise using a variety of activities (including squats) decreased stability of the knee joint, possibly due to muscle fatigue or elevated body temperature. Therefore, knee instability is not necessarily due to one specific exercise movement such as the squat. However, other factors in the execution of various exercises can cause acute knee instability.

Various forms of exercise have been shown to increase ligament strength. In animal studies, endurance exercise has been shown to increase the strength of the ligament-bone attachment, as well as augment the diameter and collagen content of ligaments. When bone-ligament preparations are tested at high speeds, they fail at a higher maximum load.

In athletes rehabilitating injured knees, closed-chain exercises, such as the squat, are currently used. During a squat, the hamstrings co-contract with other leg muscles to increase the stability of the knee, thus putting less stress on the anterior cruciate ligament.

There are certainly times in the healing of injuries when the squat, as well as other exercises that stress the knee, should be avoided. However, once soft tissues have healed, exercises that are the most effective in improving strength to protect the knee joint from further injury should be chosen.

The Stress of Squats on the Back

Another area of concern for safety in the squat exercise is the lower back. If the lift is not properly performed, the forces placed on the low back may be intense enough to cause injury. The most common errors that can lead to back problems include lifting excessive weight and leaning over too far so the weight is lifted by the back, not the legs and hips.

Squatting with resistance placed on the upper back across the shoulders does increase the compressive forces on the spine. Maintaining an erect posture helps to distribute the forces evenly on the spine and decreases the chance of injury. Forces on the lumbar spine during half-squats with a loaded barbell were determined to be 6 to 10 times body weight. To reduce both spinal compressive forces and shear forces, the athlete should have the necessary flexibility of the knee, hip and spine to maintain an upright posture during the squat.

Stress fractures of the vertebra (spondylolysis) and forward slippage of one vertebra over another (spondylolisthesis) do occur in athletes. Because athletes are generally active in a variety of ways (including resistance training), it is difficult to determine whether resistance training is the cause of these conditions. Maintaining strong torso musculature is essential to protect the spine during squatting movements. The squat program should be modified for athletes with back problems.

Back pain is a complaint often associated with the squat exercise. Sprains and strains may occur with a variety of athletic activities and are more likely to occur with sudden movements involving spinal extension and rotation. When properly performed, the squat exercise does not fit into this category. In one study, weightlifters had a relatively low incidence of back pain (eight out of 80 lifters). This study indicates that spinal flexibility, lifting with a straight back and strong paravertebral muscles help prevent back pain. In former lifters, the incidence of low back pain was less than in the general population.