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 weight vs. speed
Runworks 2005 5M Racer
San Francisco, CA
Joined: 26 Nov 2004
Posts: 1157

weight vs. speed Posted: Sat Jan 15, 2005 6:26 pm 

How much do you think a person's body weight affects their racing speed? Assuming you're fairly fit and not overweight, does it make much difference? A heavier person is likely more muscular too, and presumably can overcome the extra weight through strength.

For that matter, I wonder if anyone's done experiments having people run while carrying weights. How much would a 2 pound weight belt slow me down over the course of a marathon?


South Orange, New Jersey
Joined: 19 Dec 2004
Posts: 367

Re: weight vs. speed Posted: Sat Jan 15, 2005 8:48 pm 

When ever I go for a long run with a couple water bottles or a 70 oz camelbak I notice right away that running feels a little harder. I usually wear a camelbak for long runs of 15+ miles and my pace always seems to be off by about 15 seconds from what I expect (based on perceived level of effort) during the first half of the run. Of course, as I drink more fluid the camelbak gets lighter.

Runworks 2005 5M Racer
San Francisco, CA
Joined: 26 Nov 2004
Posts: 1157

Re: weight vs. speed Posted: Sat Jan 15, 2005 9:36 pm 

I'm totally talking out of my butt now, but I think it makes sense that the energy/effort needed to run at a particular pace should increase directly proportionally to your mass (weight). So if speed is directly proportional to energy expenditure (which it probably isn't), then a 1% decrease in body weight would mean a 1% increase in speed. Put another way, a 3:30 marathoner weighing 150 pounds would shave about 1.5 minutes off his time by dropping 1 pound. That sounds like too much, though, so there must be some other factors at work too.


Joined: 07 Jan 2005
Posts: 30

Re: weight vs. speed Posted: Sun Jan 16, 2005 8:54 am 

HI Rickshaw,
I think the weight-speed relationship is firmly established. Here is a link with info on some really elite runners.
I found that going form 152 to 142 lbs (I'm 5"7) helped alot in bringing my 10k times down. I also feel that it is easier on my knees and achilles tendons.
Two points I find worthwhile from all the stuff I've read on this:
1. If you have visable fat, then losing it will definately improve your performance;
2. Many, many runners, especially young women and young guys, have eating disorders; in fact, obsessive exercise is a disorder all on its own. Thus the weight-speed relationship gets fuzzy when you get down below the obvious fat folds. On one hand, virtually every elite runner is a lightweight skinny guy. On the other hand, there are a lot of sick skinny people who are damaging/limiting their heart/leg engine by eating too little, or worse, by purging after eating (both ends are used by various disorders).
2.5) For fellow 40+ guys, I think there is virtually zero chance of falling into an eating disorder, so my advice is: lose some weight and you'll feel better, run faster and I think you wife will be happy about it in more ways than one.

A pet theory I patched together while reading alot of stuff on this is the 'floating point' hypothesis (can't remember which doctor used that term). A given amount of exercise, including just daily, non-sports activities, uses more calorie when you weight more (you can find all sorts of calculators on the web for this, and it is cooked into the Garmin 201). Thus the more you weight the more calaories you burn. SO, for any given level of activity and any given caloric intake, you have an equilibrium weight that you'll return to even if you bing on the food/booze a bit, have a really lazy week, or engage in a fad diet for 3 weeks.
One problem is the yo-yo dieting and its impact on your equilibrium weight. When you lose weight, you lose muscle and fat (its a fact). When you put weight back on quickly, it consists mostly of fat. Now, a lbs of fat tissue requires fewer calories than muscle tissue even in a resting state. What this means is the yo-yo dieting tends to ratch up your % body fat and this lowers the baseline caloric burn rate; to re-equilibriate calories in and calories out, you gain some weight.
Increasing you're exercise, like running 5 miles a day every other day, will without changing you caloric intake result in a one-time drop in your equilibrium weight. To get lighter, you need to change your diet (hard) or run more (fun), but each increment leads to a one time change in the floating point, although you obvious are losing weight gradually for a few weeks or months as you approach the new equilibrium.

Runworks 2005 5M Racer
San Francisco, CA
Joined: 26 Nov 2004
Posts: 1157

Re: weight vs. speed Posted: Sun Jan 16, 2005 1:55 pm 

That's a very interesting article, although it stops short of providing any hard numbers for time gained per pound lost. According to their figures, the average non-active man my height (5'11") should weigh 171 pounds, and a distance runner should weigh 15 percent less than that, or about 145 pounds. I weigh between 139-143 on any given day, so I'm right about there.

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