We’re sure you have heard it before: when lunging, always keep your knee behind your toe. At the Cybex Research Institute, we hear this misconception more than almost any other. Dr. Paul Juris has examined the research related to the forward lunge in a past Truth on Fitness article and also performed a biomechanical analysis of the lunge exercise. Both reveal that the most effective way to recruit the ankle and hip musculature during the lunge is to allow some forward movement of the knee and to instruct the exerciser to effectively distribute their weight over the lead leg. So allowing the knee to move forward can be beneficial, but what if it is exceedingly stressful to the knee?
What Did We Study?
Many will argue that the primary reason to not let the knee go beyond the toes is to protect the knee. To investigate this claim, the CRI performed an experiment measuring knee forces and stresses during the lunge exercise. It was designed to examine the effects of allowing the knee to move forward, or restricting the forward movement of the knee. The unique part about this experiment is that the analysis was performed on both legs: the leg that you are lunging onto, and the back leg that is also supporting your bodyweight.
The figure above displays three positions named according to trunk and knee position (LF Leaning, Forward; LN Leaning, Neutral; UN Upright, Neutral).
What Does This Mean For Exercisers?
The CRI presented the findings of this experiment at the World Congress of Biomechanics in Boston, MA in 2015. The research demonstrated that restricting the knee’s forward movement resulted in a decrease in knee stress on the front leg. However, doing so also resulted in significantly greater stresses on the back knee! In fact, regardless of which technique was used, the total stress on the back knee was consistently greater than that of the front knee. According to this study, it seems that attempting to over-protect the lead knee only leads in more stress in the back knee.
These findings lead to the CRI’s recommendation that allowing the lead knee to move forward during the lunge is recommended. It reduces the combined stresses experienced by both knees, and more effectively recruits the ankle and hip muscles during the exercise.
The research has been accepted by the Journal of Orthopaedic and Sports Physical Therapy.
Want to learn more about CRI research? Dive deeper into knee stress and find out why planks and crunches are (almost always) a waste of time.
Avoid the 10 Worst Mistakes Made By Gyms
Do you know why your members are leaving? We analyzed all of the industry research available to understand why some facilities are successful and others struggle to retain their members.