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June 4, 2007
Lombard’s Paradox
Lombard's Paradox describes a paradoxical muscular contraction in humans. When standing up from a sitting position, both the hamstrings and quadriceps contract at the same time. However, these muscle groups are antagonistic, meaning that they should not contract at the same time.
The Rectus femoris biarticular muscle acting over the hip has a smaller hip moment arm than the Hamstrings. However, the rectus femoris moment arm is greater over the knee than the hamstring knee moment. This means that contraction from both rectus femoris and hamstrings will result in hip and knee extension. Hip extension also adds a passive stretch component to rectus femoris, which results in a knee extension force. This paradox allows for efficient movement, especially during the CrossFit Air Squat and Glute-Ham sit-up.
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.
http://guardian.curtin.edu.au:16080/cga/teach-in/lombard/
http://en.wikipedia.org/wiki/Lombard%27s_Paradox
Dr. Lombard suggested that while sitting in a chair if one should grasp his thigh so the thumb palpates the belly of the rectus femoris (top of the thigh) and the fingers palpate the bellies of the hamstring muscles (back of the thigh) he will discover the following. As one rises from the chair by means of hip and knee extension, one will feel both the rectus femoris and the hamstring muscles spring into action. It may surprise one to discover that all of these muscles are active. Further, one might expect that the rectus femoris and the hamstrings would neutralize each others action so that no movement would be possible. But they don't. This seemingly contradictory situation is known as Lombard's
Pardox.
Posted by Franklin Okumu at June 4, 2007 9:20 PM
Comments
This is completely unrelated, but I'm posting here too for the people who aren't getting the yahoo messages:
OK, the moment of departure will be upon us before you know it, so I thought I should start herding the cats. My plan is to pick up the van at about noon on Friday near SFO (where the rental agency is located) and drive to CFO, probably arriving around 1 or so. I would like to leave from there no later than 2, as I expect the drive to take 7 - 7 1/2 hours. If anyone needs to be picked up from anywhere besides CFO, you should tell me now; since I'll be driving a big van, BART stations in the East Bay or downtown Oakland are easy, downtown SF is not. I guess that's about it, my number is 510-316-6024 if you need to contact me, or use e-mail.
Sam
Posted by: Sam L at June 4, 2007 9:51 PM
Sam, I'll see you at CFO.
Franklin, life is full of paradoxes, isn't it?
Posted by: Tim R at June 5, 2007 11:39 AM
Does this explain why squats are so energy-intensive?
WoD - heavy snatch from floor. I maxed out at 94# (42.5kg) while trying for perfect form. That's 54% of BW so some way to go there.
BTW I just got my Adistars (thanks to Sam for online shopping tip) and they're awesome. I could immediately go an inch or two lower in the receiving position. I haven't tried the Dowin so can't compare but definitely feel good about the investment. Added bonus - they come in old skool CFO / Oakland Raiders colors.
Posted by: Carlo at June 5, 2007 2:51 PM
Franklin's smart.
Posted by: Jonathan at June 6, 2007 8:01 AM