Anyone that's good at physics help me out. Imagine a guy 5'10 and 150. He runs his easy days at 10:00 pace at 155 strides/minute. How much more pounding is that compared to 8:00 @155, 10:00 @180 or 8:00 @180. He just got stress fractures and he's only running 30 miles a week. I figure it's more stressful to run 6 miles in an hour with a low stride rate than to go faster at a higher rate. Any physics to back this up?
What? You are over thinking this. Just run.
Funny you should bring that up, as it's something that I've been wondering (and suffering from?) for a while. I'm 5'11 180 (which is still 30lb more than I want to be), and 8 minute miles seem really hard on my legs, but < 7:30 miles aren't too bad at all. This is while running I should add. I feel the faster running afterwards.
Mtn Dew wrote:
Anyone that's good at physics help me out. Imagine a guy 5'10 and 150. He runs his easy days at 10:00 pace at 155 strides/minute. How much more pounding is that compared to 8:00 @155, 10:00 @180 or 8:00 @180. He just got stress fractures and he's only running 30 miles a week. I figure it's more stressful to run 6 miles in an hour with a low stride rate than to go faster at a higher rate. Any physics to back this up?
A) 10:00 @ 180 = least pounding stress
B) 10:00 @ 155
C) 8:00 @ 180
D) 8:00 @ 155 = most pounding stress
This is my take without doing any math. A and D are obvious, B and C could be a toss up I suppose.
Personally - being a midget - I run ~190 @ 10:00, ~200 @ 8:00, ~210 @ 7:00.
When I started, I was around 155- 160 before I made a conscious effort to alter my stride. I did an A-B test on a treadmill using my HRM and saw 180 vs 160 took less energy even though it felt akward.
The positive effects of lower HR, faster uphills (same effort) and less stress on my feet and knees were immediate. My calves tightened up as they took more of the load and it took a few months to adjust to the new stresses.
I would think that it would be better to go faster at 155rpm because it would end up being 20% less time on your feet. I would say A, C, D, B.
Overstriding is a major contributing factor to stress fractures so 180 is going to be better at all speeds because it prevents overstriding.
Mtn Dew wrote:
I would think that it would be better to go faster at 155rpm because it would end up being 20% less time on your feet. I would say A, C, D, B.
Incorrect. Of the four scenarios you provided; (D) 8:00 @ 155 is the highest velocity at the lowest frequency which is way over-striding (relatively). Impact forces through the heel and back up the leg will be the highest in this case.
Kevin52 wrote:
Mtn Dew wrote:I would think that it would be better to go faster at 155rpm because it would end up being 20% less time on your feet. I would say A, C, D, B.
Incorrect. Of the four scenarios you provided; (D) 8:00 @ 155 is the highest velocity at the lowest frequency which is way over-striding (relatively). Impact forces through the heel and back up the leg will be the highest in this case.
Good point. However, wouldn't the fact that there would be less time running mitigate that a bit? Doing 6 miles in an hour vs. 6 miles in 48 minutes is 20% less running for the latter. Sure, it's stressful, but it's over quicker.
It's also important to consider the individual and the shoe. While it's true that weight and cadence play a pivotal role in developing stress fractures, how an individual's body goes through the detailed motions plays the biggest part in where the stress is going to manifest itself. In some cases, the runner or the shoes could be more to blame than the running itself.
I've gotten two stress fractures in my life and nearly got a third one. The first one was from jump roping a lot and then racing in spikes on a weakened foot. The next time was from running on a beach and taking a few bad steps. Most recently, I ran a marathon in what proved to be rather soft shoes over 26.2 miles and my metatarsals bent quite a bit more than is desirable over the duration.
I think there's more to every stress fracture that happens. Weight and cadence matter in every case and fixing the two can help mitigate the likelihood of injury, but in every case there is something else that made it even more likely to happen (unless the person is majorly overtraining). Fix the other stuff, sure, but make sure you address what else went into causing the fracture.