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How the muscles of the leg work when pedalling/lifting weigh(2 posts)

How the muscles of the leg work when pedalling/lifting weighPODIUMBOUNDdotCA
Nov 30, 2002 5:41 PM
I was thinking today about how the muscles of the leg work when pedalling or lifting weight. Now theres the circle diagram that illustrates which muscles are predominantly used in which part of the pedal stroke which all makes since... for the most part so here are my questions. Then doing weights in multijoint motions this all goes. Obviously a leg extension or leg raise its simple.

1) Why does the glute come into play at the top of the pedal stroke and bottom of say a squat?
2) Where is the hamstring used in a squat?
3) Why does pedalling toes down recruit more quad pulling up?

re: How the muscles of the leg work when pedalling/lifting weighup_hiller
Dec 2, 2002 1:11 PM
I am anything but an expert on this. I have never had any classes in biomechanics, and nothing on physiology beyong what I got in my HS anatomy class. But, I am a mechanical engineering student, so biomechanical stuff usually makes sense to me, and I read about this sort of thing way more than I should. Oh, and I did stay at a Holiday Inn Express last night.

pick a suspect muscle from the list on the right. the next page should show its primary function/s.

1.)Glutes (on a very basic level) originate on the back of the pelvis and are inserted into the femur. When you are at the top of your stroke or in the hole during a squat, your hips are flexed, which in effect lengthens the distance between the origin and insertion points. Since muscles function by contracting, if you use the glutes when in that position, it will shorten that distance, extending the hip from its flexed position (and causing you to stand up from the squat). The more the hip is flexed (the deeper you squat) the greater the recruitment of the glutes from the bottom of the movement. Since proper postiioning for the bike doesn't really result in a huge hip flexion, it makes sense that the glutes do not receive as much load as the quads.

2.)same thing: hip flexion. it seems weird, but if you think about the origin/insertion thing again and imagine what will happen if you make the hamstring as short as possible (which would pull the leg back), you might be able to make sense of it. (Imagine switching out different pieces of rope, all attached at the same points, and the effect that each length will have on the resulting geometry of the hip joint). That sounds about as clear as mud, I know. All this stuff makes sense (sort of) in my head, but I always have a hard time trying to explain it to anyone else. Think about a deadlift; the movement itself is incredibly similar to a squat, yet the load is placed primarily on the hamsrings instead of the glutes and quads. A general rule of thumb is that you can incorporate the hams by pushing through your heels in any movement (squat, dead, leg press, etc.) If you keep your weight more on your toes it will emphasize the quads. I haven't thought about that one enough to figure out the biomechanics of it yet, but it seems like it must have something to do with the anterior/posterior shift of your center of gravity. that website above has great video clips of proper form for squat and deadlift, BTW, in case you want to take a look and see if you can figure it out.

3.) I have no idea. I can't figure out how the quads come into that movement at all. They are mainly used for extending the knee and for flexing the hip in the final part of the range of motion in a squat or leg press, neither of which fits with pulling up on the pedal. Beats me.

I doubt this will do you enough good to make it worth the time it took me to type it. Oh well. Hope you find someone who can explain it better.