It is correct to avoid excessive forward movement of the knee during squatting and lunging movements. It is a myth, however, that you should “never let your knees go past your toes while doing a squat or lunge." This belief originated from a study that is more than 30 years old (1978 Duke University study that found maintaining a vertical lower leg as much as possible reduced shearing forces on the knee during a squat). The truth is that leaning forward too much is more likely what is truly causing the problem or injury. Read on for more information regarding these functional movement exercises and how to have correct form.
In 2003, University of Memphis research confirmed that knee stress increased by 28% when the knees were allowed to move past the toes while performing a squat. However, hip stress increased nearly 1,000% when forward movement of the knee was restricted. In addition, in group exercise, the cue “don’t let your knees go over your toes” has long been an effective general rule when trying to teach an exercise to a room full of people with different skill levels, abilities and goals. When a class has a large number of participants it is difficult to help each individual participant with their specific range-of-motion so providing a general “don’t let your knees go past your toes” cue is an effective way of erring on the side of caution for the exercise instructor.
The general pointer while performing a lunge is to try to keep your knees aligned over your second toe so that the knee is moving in the same direction as the ankle joint. However, in reality we often find the knee translating (moving) forward to the toes or beyond in a squat or lunge movement, so there are other things that must be considered. The reason for this can be attributed to the length of limbs (shinbones or tibia/fibula and the thigh bone or femur).
During lunge or squat movements, we should always emphasize beginning the movement by pushing the hips backwards before they lower towards the floor (a term referred to as “hip hinging” – see Tip below). This avoids pre-mature forward movement of the knee by shifting the hips backwards. As we continue to lower our body downward, this creates a healthy hinge effect at the knee, but there comes a time where the knee (tibia) will begin to move forward in order to maintain our balance (keeping our center of mass within our base of support). If you happen to have long limbs, then it is realistic to expect your knees to move forward over or beyond the toes. Any attempt to prevent this will result in either falling backwards or in bad squat or lunge technique which places increased loads into your low back. So, as long as you teach the lunge / squat movement correctly by first initiating the movement at the hip and avoid premature forward movement of the knee, then the fact that the knee may move forward is quite safe.
Part of the reason we lunge is to train movement patterns for our daily activities and when we climb stairs, the knee and torso naturally translate forward in parallel with each other (the torso does not remain vertical) for balance and to propel our body forward and upward. In some instances we’ve seen trainers recommend keeping the back as vertical as possible which is problematic. Our concern is that this vertical technique fails to train the neural pathways and muscles correctly, in the manner it should when you actually climb stairs or step up. Additionally, if you lack adequate flexibility in your hips (considered a mobile joint) when lunging with your torso vertical, then the lumbar spine has to contribute to achieving the mobility you need and in doing so, it will compromise its ability to stabilize the lumbar spine. This could, in fact, increase the loading on your low back.
TIP: Watch your technique in the mirror (side view) the next time you lunge. Place your hands on your hips or in the small of your back and perform your lunge. If you notice any forward tilting in your hips or an increase in the curvature of your low back, you are compromising lumbar stability and I would suggest revisiting your exercise technique.
To help learn the hip-hinge movement, stand and take a broomstick, place it behind your back, holding it with one arm above your head and the other arm places into the curve of your low back. The broomstick should touch the back of your head, the thoracic spine and the sacrum (butt). Keep your legs extended (not locked), push your hips backwards, but try not to bend the knees too much. Try to:
- Maintain contact with the broomstick against all three points (head, thoracic spine and sacrum).
- Maintain the same spacing between your hand and your lower back.
This exercise teaches you to initiate your lunge and squat by hip-hinging as opposed to driving your knees forward which places stresses across the knee and patella tendon.
When designing an exercise program for a client and including the lunge, personal trainers should keep in mind that the application of any exercise should be adjusted for the exact needs of that client. The principle of specificity dictates that the range-of-motion (ROM) of any exercise should be specific to the needs and abilities of the client. Some might have a need to restrict knee ROM if they experience any knee discomfort during exercise, while other clients might need to train to an extreme ROM to condition their joints for the angles they will experience during training or competition for a particular sport or activity. For example, a client training to learn a complicated dance routine or an athlete who plays a sport such as tennis which requires rapid changes of velocity and direction would have much different training needs than a client who just wants to lose weight and improve their health. In the case of the dancer or tennis player, they might experience a point in the routine or competition where the knee translates forward past the toes so their conditioning program needs to take this into consideration and prepare the muscles and joints to handle the forces when that happens.
A final example can help to illustrate what we’ve covered. Consider Olympic weightlifters who train to catch hundreds of kilograms of a rapidly accelerating mass during the catch phase of the snatch. This dynamic loading requires them to go into a deep squat which, combined with the proper hip ROM, will push their knees far beyond their toes. You can see this demonstrated in the following YouTube videos:
Research by Hamill in 1994 found that Olympic lifting has a much lower incidence of injury when compared to many other competitive sports such as gymnastics, football or basketball, so this extreme ROM is not a danger if the participant has the requisite hip and ankle ROM to allow it to happen. Keep in mind that Olympic weightlifters train for years to achieve the necessary flexibility for their sport. Exercising to the point where the knee can translate safely over the toes requires the appropriate progression of exercise intensity to achieve the desired ROM without any adverse affects.
For more information on the studies cited in this article and to expand your knowledge on functional fitness, we recommend the following resources to fitness professionals.
- Chiu, L., and Schilling, B. (2005, February). A Primer on Weightlifting: From Sport to Sports Training. Strength and Conditioning Journal/National Strength and Conditioning Association, 27(1), 42-48.
- Fry, AC., Smith, JC, S., & Schilling, BK. (2003, November). Effect of knee position on hip and knee torques during the barbell squat. Journal Of Strength And Conditioning Research / National Strength & Conditioning Association, 17(4), 629-633.
- Hamill, B. (1994, January). Relative Safety of Weightlifting and Weight Training. Journal of Strength and Conditioning Research/National Strength and Conditioning Association, 8(1), 53-57.
- McLaughlin, T., Lardner, T., & Dillman, C. (1978, May). Kinetics of the parallel squat. Research Quarterly, 49(2), 175-189.
- Gary Gray, renowned Physical Therapist recognized internationally for being "First in Function"
- ACE’s Functional Training & Assessment Workshop
- ACE’s online exercise library