It is probably one of the most common coaching points you hear PTs and group exercise instructors shout out. Yet if you watch how children squat down, they naturally allow their knees to go over their toes. And when we walk downstairs our knees go over our toes– so is it a myth or fact?
Early research carried out by McLaughlin, Lardner and Dillman (1978) discussed the forces acting on the knee and encouraged keeping the shin as vertical as possible to reduce stress on the knee. Another study by Fry A.C., Smith J.C., Schilling B.K. (2003) called ‘the effect of knee position on hip and knee torques during the barbell squat’ examined joint kinetics (what happens to knees) during back squats under two conditions with the purpose of putting actual numbers to the forces acting on the knees and hips. The two conditions were:
Fry et al found that not allowing the knee to go over the toes increased anterior lean of the trunk that translates to a 22% decrease in stress upon the knee but a 1070% increase in stress going through the hip. So even though you could argue that there is less stress on the knees, the transferred forces were more than tenfold to the hips and lower back. In their summary, Fry et al stated “In order to optimise the forces at all involved joints, it may be advantageous to permit the knees to move slightly past the toes when in a parallel squat position.”
What is not commonly quoted from this research, however, is that it was done with a static squat, the equivalent to a ski sit with a barbell. So you could even question the viability of these results for real life as you would question when real clients would do a static squat with a barbell.
If your knees can go over your toes, where do the injuries come from? The National Strength and Conditioning Association made this statement about squats with the knee going over the toes:
"Some reports of high injury rate may be based on biased samples. Others have attributed injuries to weight training, including the squat, which could have been caused by other factors. Injuries attributed to the squat may result not from the exercise itself, but from improper technique, pre-existing structural abnormalities, other physical activities, fatigue or excessive training."
One factor that does increase injury is any form of rotation on the knee during squats/lunges, supported by studies by Fleck and Falkel (1986) and Signorile et al (1995). They concluded:
"Extreme outward toe point greatly reduces stability; it does not allow the proper drift of the hips as the lifter descends... Extreme inward toe points are equally dangerous, coupling the same problems of stability, base size and lower body drift with the added danger of bringing the knees together...this movement would place high stress on all connective tissue."
From this we can gather that a key coaching point is that rotational movements are bad for knees and so you would encourage the knee to move along the sagittal plane in line with the 2nd toe.
What does this mean to you as a professional coach? Firstly, as with any exercise, you would question the suitability of the squat/lunge for your client based on their exercise history, current levels of fitness, current injury status and their goals. Then, when using the squat/lunge, you can consider this:
However, you can use the knee position to help with coaching. For example, if someone is lunging and their knee is well beyond their toes then:
The same applies to a standing hip flexor stretch. If the client’s knee is well beyond their toes then:
Even though the ‘knees over toes’ coaching point was originally based on research, the bigger picture of the effect on the hips and lower back has since been ignored. Good technique and good coaching can make the squat a very effective exercise. It will be your judgement that will make it so.
Fleck, S.J. and Falkel, J.E., 1986 Value of resistance training for the reduction of sports injuries. Sports Medicine, 3, 61-68
Fry A.C., Smith J.C., Schilling B.K. 2003 Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res. Nov;17(4):629-33
McLaughlin, T.M., T.J. Lardner and C.J. Dillman 1978 Kinetics of the parallel squat. Res. Q. Exerc. Sport 49:175–188.
National Strength and Conditioning Association. The Squat Exercise in Athletic Conditioning, NSCA Position Statements
Signorile J.F., Kwiatkowksi K., Caruso J.F., Robertson B. 1995 Effect of foot position on the electromyographical activity of the superficial quadriceps muscles during the parallel squat and knee extension. J Strength Cond Res. 9:182-187