The evidence accumulated in the various phases of this study strongly suggests that the deep-squat exercise, especially as done in weight-training and as used in athletic or other physical conditioning programs, should be discouraged because of its deleterious effect on the ligamentous structures of the knee.

If the ligaments are the first line of defense against knee injury and function in unison with the muscles to maintain stability, then the deep-squat exercise is not a specific exercise suitable to build up strength of the knees since deep-squatting tends to weaken the ligaments and hence make the knee more vulnerable to injury.

Also of significance in later life are the implications of the knee instability so created. After the completion of school when physical activity decreases, general muscle tone and strength decrease, and the stability of the ligaments becomes increasingly important. If the ligaments have been weakened and stretched in school athletics, then abnormal movement is possible within the joint throughout life with the result that internal derangements, osteo-arthritis, and the like, may be more frequent.

There are other exercises similar to full-squat that have a comparable effect on the knee ligaments if carried out in conditioning practices. These include the duck-waddle, squat-jump, and deep-knee bends. These have been used in athletic conditioning in past years but are gradually being eliminated from the programs of the more astute coaches and trainers.

We suggest that the squat exercise used in weight-training and in athletics and conditioning programs be modified so that this exercise is done with the feet straight ahead and the squat limited to a half (thigh parallel) knee bend. This will strengthen the muscles but not place abnormal stresses on the ligamentous structures of the joint.