Typically we’re taught that muscles work in pairs- as one contracts the other relaxes to facilitate movement- this is referred to as ‘reciprocal inhibition’. However there are certain circumstances where this might not be the case (force coupling of the local and global spinal muscles may well be an example). Another example is that of the relationship between the quads and hamstrings through a flexion-extension cycle such as a squat.
LOMBARD’S PARADOX refers to the biomechanics of a squat patterns where there is simultaneous contraction of both the anterior and posterior thigh muscles. The theory is as follows:
• The hamstrings have a greater moment arm than the rectus femoris (RF) at the hip
• The quadriceps have a greater moment arm at the knee in comparison to the hamstrings
So what?
• As the hamstrings act on the hip but attach farther away from its axis of rotation than the RF; they can generate a greater amount of force than the RF. This allows hip extension to take place
• At the knee, the RF (as well as the VMO, VL and VI) attach further away from the axis of rotation in the knee than the hamstrings do, and as such can generate more force, allowing knee extension to take place.
Consequently the result is a contraction from both the quads and hamstrings that will result in hip and knee extension. Additionally, hip extension also contributes a passive stretch component to RF.
APPLICATION:
This paradox allows for efficient movement, especially during gait. Anything that requires knee/hip flexion cycles- cycling, running, weightlifting
A great paper to read that discusses relative contributions of the lower body muscles (as expressions of MVC) is: D.G.E. Robertson, Jean-Marie J. Wilson, and Taunya A. St. Pierre. “Lower Extremity Muscle Functions During Full Squats” Journal of Applied Biomechanics, 2008, 24, 333-339. 2008
REFERENCES
1. Lombard, W.P., & Abbott, F.M. (1907). The mechanical effects produced by the contraction of individual muscles of the thigh of the frog. American Journal of Physiology, 20, 1-60