quote:Originally posted by zgator: I'm in fair shape and I really want to test this, but I don't think the janitorial staff in my office has been doing such a great job of cleaning the floors lately.
If I recall correctly, you also test-drove my fingertip/visual illusion experiment.
Fabulous. Gold star for you! *grin
Posts: 14017 | Registered: May 2000
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posted
Let's make some assumptions. A man who is 6-ft tall will likely have his center of gravity (COG) at about 3 feet. If he weighs 170 lbs, the moment from his toes would be 510 ft-lbs. If his arms are at about 5 feet, he would need to push with a force of 102 lbs.
On his knees, the COG would be about 2 feet from the point and the arms would be about 4 feet. Assuming the legs below the knees weigh about 10 lbs each, that give a weight of 150 lbs, which in turn give a moment of 300 ft-lbs. He would need to push with a force of only 75 lbs now.
Now he's well-built with a large upper body so he weighs 200 lbs and the COG is now at 3.5 ft for regular pushups and 2.5 ft for knee pushups. That gives a necessary force of 140 lbs and 112.5 lbs for regular and knee pushups, respectively.
The percentage difference between the two is smaller for the well-built man. Which means the regular guy would see a bigger difference between knee pushups and regular pushups.
Disclaimer: I have no idea how close those COG's are to reality.
Posts: 4625 | Registered: Jul 2002
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posted
You need to figure in tendon attachment points and angles of joint motion, etc., to create a feasible model, in my opinion.
Posts: 14017 | Registered: May 2000
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posted
The main problem that I can see is that a regular pushup is more of a benchpress motion (arms perpendicular to the torso), and the girl pushups are more of a decline motion (maybe 15 degrees down from perpendicular). Therefore, it does take more force to create the same motion, but the moment arm is shorter. I'd call it a wash, but in practice I think girl pushups are simpler.
I actually can't wait until I get home from work to try this. I'm in better than average shape (though I hesitate to apply the 'well conditioned' tag), so it might be a better measure.
Posts: 5462 | Registered: Apr 2005
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zgator, I don't think you can make the assumption that a "normal" 6' tall man's COG is at 3', either. The whole point of COG is that it is not "right in the middle" like you would expect it to be. For most 6' guys, 3' is going to be somewhere in their upper legs. The amount of mass above that point is going to be significantly more than the amount below.
In other words, I think your numbers are pretty much useless. Posts: 7954 | Registered: Mar 2004
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Blayne Bradley
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posted
woot, now I can join the reserves quicker.
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quote: You need to figure in tendon attachment points and angles of joint motion, etc., to create a feasible model, in my opinion.
Hey, I did this in 5 minutes. Cut me some slack.
quote: In other words, I think your numbers are pretty much useless.
Actually, they're not useless. The better built a man is, the higher the COG will likely be. Let's face it - most men who work out do not spend anywhere near as much time on their lower body as their upper body. If you change what I assumed to 3.5 and 4 feet, the concept still applies in that the higher the COG, the less difference there will be between the required forces.
Of course, JT's point about the angle is a good too.
Posts: 4625 | Registered: Jul 2002
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posted
For the average adult human, CG is somewhere in the vicinity of an inch or two above their belly button.
On average, men have higher CGs than women. Many women have CGs that are actually at or below their belly button.
Can someone explain again the difference between the two types of pushups? I have no idea which kind I do.
Posts: 32919 | Registered: Mar 2003
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Pushups on knees: 55 (I probably could have done a couple more but I got bored)
"Regular" pushups: Usually around 70.
Those girl pushups are hard (Yup, decline all the way). If that's what girls are fighting against when doing "regular" pushups, I'm impressed. My shoulders REALLY wanted to kiss the floor.
Posts: 1156 | Registered: Jan 2004
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quote:Originally posted by Strider: so that fitness test was something that people had to do before they were allowed to go to basic training?
They still have to do it before thay begin basic training. Potential recruits who fail the test will be admitted but have to undergo special physical training before being allowed to begin basic.
Posts: 1794 | Registered: Jul 2002
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posted
The key with the modified push-up is keeping everything STRAIGHT. I've seen a lot of people do these push-ups, who say they can to a bajillion of them, but they do it bending at the waist. A lot of times, you don't realize that you're not keeping everything aligned unless someone is there to tell you.
The difference between the push-ups is that the modified push-up...let me find a picture.
quote:Originally posted by ketchupqueen: Well, for instance, dropping the running could allow asthmatics in, and as long as they're not on the front lines but in an at-home support position, with the proper medication asthmatics might be okay.
If they have issues with asthma then they probably won't be let in. However, if they are like me, and have had no issues with their asthma for quite a while, then who cares? Put them on the front line. I'm in on a waiver for having had asthma. I have had one issue with it my entire time in. Other than that, I don't let it get in the way.
Posts: 2208 | Registered: Feb 2004
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