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Old 03-15-2018, 12:49 PM
Contemplation Contemplation is offline
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Does a higher center of gravity help you run faster?

Many articles claim that having a high center of gravity helps someone run faster because they are able to lean more of their weight forward. When somone runs, at some point in their stride, both feet are in the air and their center of gravity is in front of them. A high center of gravity is supposed to help them both land faster on the ground, and gain more distance with each of these strides.
Som articles say this is why West African sprinters are better. They have longer legs, which gives them a higher center of gravity.

But longer legs doesn't always mean a higher center of gravity.

What if someone had short legs and a very large head? Would they still benefit from a higher center of gravity?
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Old 03-16-2018, 12:54 AM
Contemplation Contemplation is offline
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a little bump
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Old 03-16-2018, 05:47 AM
Darren Garrison Darren Garrison is offline
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Wasn't able to google them up yesterday, but a year or two back there was a study circulating in the popular science press about research on fast runners showing that the fasterness came from higher "leaps" as they ran, not from more strides per unit of time. (In other words, the trick was to stay in the air longer, not to move your legs faster.) Don't know how or if center of gravity would effect that.
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Old 03-16-2018, 06:17 AM
Isilder Isilder is offline
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Correlation is not causation.

Ok, we know that there's no such event as the 40 metres sprint, because shorties would be able to win that. During the amateur events when a short sprint race was tried, the tall people protested saying that the short athletes had the advantage.

So the short legged atheletes are relegated to weights, and the sprint is 100 metres or more.

The cause is not centre of gravity. The cause is that the long leg is more efficient. First, the legs are just naturally more efficent, as they move the person a greater distance for each stride. Second, the increased muscle length of the taller body is efficient for having more muscle as a % of body mass... the athelete has a similar size of head,shoulder,rib cage, hip, lungth,intestine, radius (eg of the butt..) but taller means quite a bit more muscle.

I see some people go on and on about the taller legs giving an angle advantage. No, the angle is the balance of forces. Sure its torque, but its not torque like an engine produces an excess of torque... its a torque that must be closely balanced with air drag, and speed. Sure Usain bolt leans forward.He's tall and light, but that means he has a lot of air resistance acting higher up.. He is less stable, it could only be a disadvantage, but it turns out its pretty much the same as anyone else, you just increase your lean instinctively (Or did you programme it into your brain as a toddler ??).. so no disadvantage. Just not an issue.

Usain Bolt's evolutionary history may have put some super strong muscle into his body- his light weight suggests he should not be so strong. Hence he could sustain the high frequency leg movements of sprinting - it uses less power to move his lighter legs at that frequency - he gets them going at top frequency faster, and he doesn't burn out in the short sprints. Its also why he doesn't do long distance . IT seems he is light because his body doesn't have the slower strength muscles - hes full of fast twitch and can't pace himself.

Last edited by Isilder; 03-16-2018 at 06:20 AM.
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Old 03-17-2018, 03:32 PM
Contemplation Contemplation is offline
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Quote:
Originally Posted by Isilder View Post
Correlation is not causation.

Ok, we know that there's no such event as the 40 metres sprint, because shorties would be able to win that. During the amateur events when a short sprint race was tried, the tall people protested saying that the short athletes had the advantage.

So the short legged atheletes are relegated to weights, and the sprint is 100 metres or more.

The cause is not centre of gravity. The cause is that the long leg is more efficient. First, the legs are just naturally more efficent, as they move the person a greater distance for each stride. Second, the increased muscle length of the taller body is efficient for having more muscle as a % of body mass... the athelete has a similar size of head,shoulder,rib cage, hip, lungth,intestine, radius (eg of the butt..) but taller means quite a bit more muscle.

I see some people go on and on about the taller legs giving an angle advantage. No, the angle is the balance of forces. Sure its torque, but its not torque like an engine produces an excess of torque... its a torque that must be closely balanced with air drag, and speed. Sure Usain bolt leans forward.He's tall and light, but that means he has a lot of air resistance acting higher up.. He is less stable, it could only be a disadvantage, but it turns out its pretty much the same as anyone else, you just increase your lean instinctively (Or did you programme it into your brain as a toddler ??).. so no disadvantage. Just not an issue.

Usain Bolt's evolutionary history may have put some super strong muscle into his body- his light weight suggests he should not be so strong. Hence he could sustain the high frequency leg movements of sprinting - it uses less power to move his lighter legs at that frequency - he gets them going at top frequency faster, and he doesn't burn out in the short sprints. Its also why he doesn't do long distance . IT seems he is light because his body doesn't have the slower strength muscles - hes full of fast twitch and can't pace himself.
So a higher center of gravity by itself is not an advantage.
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Old 03-17-2018, 04:26 PM
Stranger On A Train Stranger On A Train is offline
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A higher center of graivty by itself is not an advantage; however, while running the body has to remain dynamically stable which means on average the center of mass should be balanced over the maximum force of the stride so as to not lose too much effort in preventing following forward. For sprinters in particular, this means starting in a crouch and running tilt forward (at 35 to 40 degrees) with the thrust of the leading foot pushing forward and slightly up directly through the center of mass just past the point at which the foot makes contact with the ground and through the extension cycle of the leg, so the higher the center of mass is above the pivot (hips), the longer a stride a sprinter can have, and the fewer strokes he or she needs to take to cover the same distance (although they have a longer return for the trailing leg). This is different from a marathoner who runs essentially upright and uses the stored potential energy of the body to spring from side to side.

The primary thing that dictates the absolute speed of a sprinter is the amount of power the leg muscles can generate during the stride, and this has to do with the proportion of fast twitch anaerobic (Type IIb) fibers that are fully developed in the leg muscles. For a given body shape and torso-to-leg length there is an optimum form for sprinting, and there may be some kinematic limitation on how much of the stride can be usefullly applied but the recruitment of muscles to develop motive force is the primary limiting factor.

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Old 03-18-2018, 07:09 PM
Wallaby Wallaby is offline
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Usain Bolt (and every other sprinter) does not lean forward when sprinting at top speed. (The do during the acceleration phase when raising their COG from the crouch position. If they stood up immediately, they would be moving their COG backwards, and basically be stationary for the first half-second or so. A standing start is faster for the first 20-35 metres of the race).

The hardest part of raising the COG is the head - this is a 5-6 kgs lump sitting (wobbling) on top of a set of relatively weak stabilising muscles (neck), with no muscles of its own to assist in the running motion, transfer of weight or balance. Most people find a comfortable position when walking or running (or even standing) is to hold the head slightly forward of the COG - this leads to the impression that runners 'lean forward when running'.

I you watch any top sprinter on Youtube you will notice that they are nearly exactly upright once they reach maximum or near-maximum speed. The foot strikes the ground slightly in front of the body, and applies force only while the foot is in front of the body. The keys to maximising sprint top speed are:
1) Applying maximum force to the ground each stride (how hard you can push off)
2) Applying that force quickly (how fast you can push off)

Using these basic ideas you need to be a) strong and b) have quick-acting muscles - the fast-twitch muscles, gene ACTN3 etc. The sprint action that top athletes use is a learned action quite a bit different to the 'natural' fast running style we all use from the age of 3.

Long legs have pros and cons - longer strides, but also longer cycle times. The one definite advantage they do have is that fewer strides mean fewer strides to fatigue the body - meaning you can hold maximum speed for longer (it's a slight advantage, but it seems to be confirmed by the studies - yes there are factors like longer legs are heavier and take more effort etc, but overall - better to have long legs. The advantage is very slight).

Carl Lewis was 3 inches shorter but 5-6 KGs heavier than Usain Bolt. Ben Johnson was about 4 inches shorter than Lewis, but probably the same weight, or even heavier, and significantly stronger (illegally). He was faster, too.

It's all a case of balancing out the pros and cons of the various factors - good muscles mean more force, but more weight. Too much muscle mass restricts speed of and range of movement. Flexibility is important - too much flexibility can mean less stability in applying force to the ground. Etc, etc.

Top sprinters are freaks of nature, who have been trained. Usain Bolt is a well-trained freak among freaks.
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