Will a runner with a lower body weight have a lower risk of injury than a heavier person, all other measures of health, fitness, and experience being equal?

October 17, 2007 10:40 PM

Will a runner with a lower body weight have a lower risk of injury than a heavier person, all other measures of health, fitness, and experience being equal?

Take one 5'11" runner at 135 lbs (the low end of the healthy weight range) and one 5'11" runner at 180 lbs (the high end). If both are equally healthy, in shape, and have the same experience with running, will the lighter runner have a significantly lower risk of injury than the otherwise equal, but heavier runner?

posted by sequential to Health & Fitness (10 answers total)

All other things being equal, including the intensity of training / running, the lighter runner will have fewer injuries. Running is a high impact sport, and most running injuries are due to stress placed on bones, ligaments, and muscles in the feet, ankles, shins, and knees. The heavier the runner, the greater the stress on these parts.
posted by zippy at 10:46 PM on October 17, 2007

Is the heavier runner the same as the lighter runner with 45 lbs of fat added or is the heavier runner more like a scaled version of the lighter runner (obviously, not in height, but in having larger muscles, joints, etc.)?

Subjecting the same joints to higher forces (due to 45 lbs of extra fat) is clearly going to cause more injury, but if the heavier runner has joints that are strong enough to compensate for the extra weight then I don't see why there should be a difference in injury rates. You'd also have to consider that the lighter runner would have very little muscle (5'11" at 135lbs is pretty skinny) and may be more susceptible to injury due to the lack of strength and stabilization.
posted by ssg at 10:50 PM on October 17, 2007

Response by poster: Can the heavier runner increase strength, balance, and flexibility training to the stressed areas enough to compensate for the difference in risk of injury or is weight really the determining factor?

Excellent point, ssg. I don't know if I can say definitively that the two can be in equal shape, but let's say they each had the same body fat and proportional amounts of muscle. If they were each 15% body fat, the difference in the amount of fat would be:

(180 * .15) - (135 * .15) =
27 - 20.25 =
6.25 lbs

Then again, 45 lbs of muscle weighs exactly the same as 45 lbs of fat, so your point may still be completely valid.
posted by sequential at 11:01 PM on October 17, 2007

Lighter runner has less impact injuries in general.
posted by Ironmouth at 11:02 PM on October 17, 2007

There aren't any controlled studies that conclude that body mass, alone, is determinant of injury rates in runners. Indeed, there is some evidence that factors such as correct technique, choice of footwear (or the complete lack thereof), running surface, and prior training history and injuries, may be far better determinants of the likelihood and types of injuries runners actually sustain, than weight. In particular, stride "impact" has proven to be particularly amenable to shoe design and changes in technique for stride mechanics.
posted by paulsc at 11:22 PM on October 17, 2007

A lot of people think that adding more muscle to your legs prevents injury. I can't cite anything, but I'm pretty sure that it's now accepted dogma that runners who occasionally do lunges, deadlifts, etc. are injured less often; and these runners would have more muscle and thus would weigh a little more. So this is one more factor to consider.

So it might depend on why your heavier runner is heavier.
posted by creasy boy at 11:51 PM on October 17, 2007

Our bodies are remarkably adaptable. I wouldn't be surprised if the muscles, tendons, ligaments and bones of the heavier runner react to the regular stress of the workout by becoming more robust. I say this as a guy who has been as much as 235lb, and never injured himself running as much as 5 miles. Anecdotal, I know.
posted by knave at 12:24 AM on October 18, 2007

I've run from 165 lbs to 225 lbs (same height). I definitely had to adapt shoes, stride and weight training at the high end of the range to avoid injury. Also, at the low end of the weight range I could run on concrete. At the high end I have to run on level asphalt with no sideways slope.
posted by BrotherCaine at 12:37 AM on October 18, 2007

there are so many more variables than simple weight. shoes, technique and bone structure come to mind. the only thing we know for sure here is that the heavier runner impacts his feet with more weight.

ask this question over at http://forums.runnersworld.com

personally, I feel more fragile since I lost weight.
thanks to running, btw.
posted by krautland at 1:32 AM on October 18, 2007

Bones adapt and remodel based on the levels of stress they get, so a heavier person may have more robust bones than a lighter person. The difference in weight, which changes the strain on the bone, may be offset by the strength of the bone. It's hard to say what would happen if "all things were equal."

But answering practically, the risk for bone injury in running is greatest when a person who typically doesn't exercise suddenly begins a regimen of intense strenuous activity. So if both a normal BMI and high BMI person started the "run a marathon by 6 months to support breast cancer" training program, the normal BMI person may have a lower risk of injury.

Another fine point is that some professional athletes who are underweight may not have adequate calcium intake. Specifically underweight female athletes with amennorhea have inadequate bone strength related to the calcium utilization, and are at additional risk for fractures.
posted by alex3005 at 2:05 PM on October 18, 2007