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Research Summary: Trunk Position and Shank Angle Alter the Biomechanics of the Lead and Support Limb During the Forward Lunge Exercise

In research presented at the World Congress of Biomechanics in Boston, a group of researchers led by Cory Hofmann of the Cybex Research Institute sought to investigate the differences in the biomechanics of both the front and back legs during different step-forward lunge techniques.

“There are a lot of individuals claiming that there is a correct way to perform this exercise,” Hofmann stated. “Our data suggest that the technique that one chooses should be dependent on the goal of the exercise, as they all will result in different outcomes.”

Studying Three Lunge Positions

The group tested three different conditions:

  1. Bending forward at the waist and allowing the lead knee to move forward over the toes
  2. Keeping the upper body upright while allowing the lead knee to move forward over the toes, and
  3. Keeping the upper body upright while maintaining the lead knee directly above the ankle. 

The latter of these is traditionally considered the ‘proper’ way to perform the exercise, with the first two conditions incorporating some elements that might be considered bad form.

The researchers measured the motion of the exerciser’s joints and the forces that they created with the ground under both the leading leg and the supporting leg. The group then used this information to calculate demand to the different muscle groups and stress to the knees of both legs. The study is one of the first to analyze both the front and back legs during this particular exercise.

What Did We Find?

Bending forward at the waist and allowing the knee to move forward over the toes resulted in the greatest demand to the calf and glute muscles. The price to pay for this increased muscular demand is an increase in knee stress of the leading leg, which was much greater than that of the traditionally correct technique. Despite this reduction in lead knee stress, the ‘proper’ form lunge resulted in stresses in the back knee that far exceeded that of the front knee in any other condition.

“Our results show that maintaining an upright trunk and keeping the knee over the ankle resulted in a much more stressful environment for the supporting knee,” Hofmann said. “This is especially important because the back leg is under load for a much longer duration than the front leg. It seems that many are attempting to protect the front knee at the sacrifice of significantly increased compressive loading under the back kneecap.”

“In all honesty, the forward lunge results in high stresses at the knee regardless of the technique utilized,” added Hofmann. “Considering that, I’d prefer the option that gives me the most demand to the glutes and calves.”

Final Takeaway

These findings suggest that the commonly held belief that the knee should never go beyond the toes during the forward lunge might need to be reconsidered, depending on the objective of the exercise.

Dive into more CRI research. Learn how holding on to treadmill handrails affects calorie burn and how we built a treadmill for serious runners.

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