Can squats be bad for your knees?

Q: What is your opinion of deep knee squats for kids in high school and junior high? We have three athletes that have developed knee problems since starting a program that has been established by a former Olympic lifting coach. – Greg

A: Thanks for the question Greg. Because opinions are of little assistance in matters such as these, let’s start with the facts, which are numerous. Opinions just lead to arguments on the level of my “guru can beat up your guru”. First of all, any exercise analysis must be based upon determining potential risk weighed against potential benefit.

Fact #1 – During movement through the full range of any joint motion, one’s strength changes dramatically. In the case of the compound movements such as the squat, basic mechanical analysis shows that we get progressively weaker as we “fold up” like an accordion. Therefore, we are the weakest when we are all the way down at the bottom of the squat. Although training will improve our overall strength, this general strength profile can not be altered. We will always be weaker at the bottom of the squat than at the top (or in a sense, the weight will be heavier at the bottom than at the fully erect position). Therefore, the amount of resistance chosen becomes a key factor in whether or not an individual will be able move full range of motion correctly on any exercise.

Fact #2 – We must look at the joints involved. Barring any specific individual medical issues, the average knee can move through approximately 120-140 degrees of motion (everybody’s a little different). However, a closer look at the architecture of the knee reveals that not every point along that range is created equal. The knee is composed of the end of the femur (thighbone), which has two rounded regions called condyles, and the end of the tibia (lower leg) which is slightly cupped to accept the condyles. As the knee bends, different aspects or areas of the knee make contact and accept force. When the knee is near straight the end of the condyles contact the tibia. Because this region has a greater surface area, it has a considerable ability to disperse force. This is the part of the knee that accepts the forces of impact when we walk and run. It’s pretty much designed for it. When the knee is bent to a considerable degree, the backsides of the condyles contact the tibia. This portion of the condyles is more rounded and offers a smaller contact surface to accommodate not just the same forces, but what will be even greater forces as we bend down to this point of contact.

Fact #3 – There are two types of cartilage within the knee. If you have ever looked at the end of a chicken bone you’ve probably noticed a smooth, white “Teflon-like” covering. We have the same “hyaline cartilage” covering the contact surfaces of the knee. This serves two purposes: to decrease friction for smooth sliding of the joint surfaces, and to act as a cushion. It is common knowledge among orthopedic surgeons, however, that the thickness of this cartilage differs as it surrounds each aspect of the femoral condyles. The cartilage covering the back of the knee is thinner than that covering the end of the condyles. This corresponds with the shape of the joint for the same reason mentioned above. Thicker cartilage is offered as a cushion on the end of the bone where impact occurs during walking, etc. Therefore, the back of the knee, which is visited less frequently throughout normal activity, has less tolerance for wear. Long term wear of this cartilage covering/cushion is associated with arthritis. In many older folks it is the cartilage at the very end of the bone that wears due to normal walking, etc. Athletes will have varying wear-patterns that are distinct to their sport and the unique range and forces to which their knees are subjected. In many sports it is the back of the knee that wears due to continual force application at this extreme range. This is why certain athletes have “90 year old knees” on an otherwise 35 year-old body, depending upon the requirements of their sport.

The second type of cartilage is the meniscus. This a C-shaped ring (actually two of them … referred to as menisci) around the perimeter of the joint. These are most commonly torn when the knee is in extreme flexion, under a compressive load, and any slight torsion or medial/lateral forces are introduced into the knee. In a perfectly performed squatting exercise, these forces would not be expected to occur. If perfect knee alignment is not practiced one each and every inch/degree of each and every repetition, expect trouble. If you’ve ever watched someone from the front as they squat, leg press or lunge in the gym and as they extend the knee from the bent position it waivers, wobbles, or moves side to side even a fraction of an inch, you’ve observed the problem. This individual has a lot of work to do on control, or the skill/motor pattern, of the movement before they go to extreme ranges of motion or challenging loads. Lower extremity alignment during exercise must be insured through conscious effort. (By the way, this appears to be one of the reasons that most branches of the military no longer subject recruits to the old “duck-walk” exercise. Apparently the cost of all the knee surgeries that they were inducing finally out-weighed the benefits of the exercise.)

Fact #4 – The kneecap or patella can become an issue in extreme flexion of the knee. One reason is the fact that the compressive forces on the patellae reach eight times the amount of resistance applied (body weight plus additional load) when the knee flexes to 130 degrees. This can increase the risk of, or exacerbate a prior condition of, chodromalacia patellae. This is a roughening of the hyaline cartilage that covers the underside of the patella and is characterized by a grinding noise or sensation during knee extension. Another fact is that for many individuals, extreme flexion of the knee creates a situation where the femur no longer makes contact with the patellae. Instead the quadriceps tendon rides across the end of the femur.

Fact #5 – Puberty and deep squats, anatomically speaking, don’t mix. A great deal of one’s ability to squat depends upon his/her individual mechanical/anatomical structure. Many automatically relate this to an individual’s overall height, but it is more a matter of lever or bony proportions. The longer ones femur is in relation to the trunk and the tibia, the more difficulty he or she will have in “folding these levers upon each other”. More accurately, the longer the femur, the further forward the knee must travel and the further backward the hips must travel as the thigh become horizontal at the bottom of the squat. This is key because the further the joints move from being directly below the weight, the more forces they will be subjected to.

Furthermore, if the femur is longer than the trunk, the trunk will have to move even further from vertical. As the trunk gets closer to horizontal the shearing forces in the spine increase as does the difficulty in maintaining proper spinal alignment. If the femur is longer than the tibia, knee range is increased dramatically and increases even further.

Keeping these proportions in mind, you can easily look around a gym and see who’s built to squat and who’s not. Just ask who feels their back vs. who feels their quads during squatting and you’ll see a correlation with body lever proportions. But, relative to your question, the key is that as we go through puberty virtually no one is built to squat, at least not to an extreme depth. As humans go through puberty the skeletal structure grow disproportionately. It’s been the subject of jokes throughout history. First the feet practically double in length, then the tibia and femur sprout, but the trunk and shoulder width still look like that of an eight year old. Finally by 16-20 years of age the trunk and shoulders pretty much catch up, realizing the proportions that the individual is likely to carry throughout life. Anyone who truly understands biomechanics, is even remotely observant of individual’s growth/proportion changes, and realizes that different structures require different exercise prescriptions would not prescribe the same depth of squatting for any group of people, much less a group of teens.

Taking all of these facts into consideration, I’d say that most individuals would be able to do full squats (if perfectly controlled) with their bodyweight (little or no additional load). Deep squats with additional weight are not ideal for the average person and even more risky for a teenager. But remember “deep” and “weight” are relative terms. As range changes, the amount of weight tolerated will change. Many high level athletes will benefit considerably from deep squats, but there are many reasons they’ve achieved a high level of performance, not the least of which is a genetic structure (joints, tissues, etc.) that offers greater tolerance for extreme ranges and extreme force.

Although these next points would be considered more as “perspectives of a true professional” than as facts, they weigh heavily into the topic.

An exercise professional should not confuse sports extremes with fitness. Running can be health and fitness inducing. Marathons on the other hand, although great sports, cannot be considered healthy for the average person and should not be imposed upon everyone. But this perspective is true of anything taken to an extreme. Sitting is restful, but eight hours a day for twenty years is not at all healthy. The squat is more than a great exercise, it’s part of life (sitting, lifting, etc.). But when the squat is immediately and automatically equated with a specific sport (powerlifting or Olympic lifting) and the rules or ranges specific to that sport are automatically imposed upon all . . . well, this is malpractice. Along with high-level skill acquisition, a specific set of genetic traits are required for successful and reduced risk performance in any sport, from muscle fiber predisposition to skeletal structure.

Imposing one’s bias, interest, or “gift” upon another without modification based upon consideration of the facts, as well as individual differences, is clearly wrong. Just because someone loves football, was good at football, and was built for football doesn’t mean everybody who wants to be a little stronger, faster or more powerful, should, or could, train even remotely like a football player. They can, however, achieve improvement in these areas through exercises modified for their individual structure and neurological ability.