An exciting new study from the University of Wisconsin is sure to add fuel to discussions about proper running form, running stride, and foot placement. The research team found that runners who simply shortened their strides (by increasing stride frequency by 5 to 10 percent) achieved many presumably positive changes in forces and motions. They wrote: "Many of the biomechanical changes we found when step rate increased are similar to those observed when running barefoot or with minimalist footwear." [Photo right: Dr. Bryan Heiderscheit.]
The subjects in the study were 45 healthy, recreational runners in their early 30s who averaged about 15 miles a week of running at a preferred pace of about 9:15/mile. They maintained this pace on the laboratory treadmill, but prompted by a metronome, also ran with a stride frequency 10 and 5 percent less than their normal frequency (which was 173 strides/minute) and 5 and 10 percent higher. While the subjects ran with these stride manipulations, the investigators measured many forces and motions produced by their running strides. The researchers concluded: "Our findings demonstrate that subtle changes in step rate can reduce the energy absorption required of the lower extremity joints, which may prove beneficial in the prevention and treatment of running injuries."
Some of those findings:
*** As stride length decreased, the runners bounced less, landed closer to their center of mass, and produced lower braking forces against the ground.
*** A shorter stride allowed the knee to do less work absorbing energy. A 10 percent higher-cadence stride allowed the hips also to do less work.
*** A shorter stride allowed the knee to bend less during stance, and decreased many hip motions.
*** A 10 percent shorter stride caused runners to rate their perceived effort higher. However, the researchers believe this might be a temporary adaptation phase, and note other research supporting this point.
Here's a box that summarizes some key findings of the paper, which has been published online by Medicine & Science in Sports & Exercise, and will appear soon in the print journal. Below the box, you'll find a long interview with the primary investigator, Bryan Heidersheit, PT, Ph.D. of the University of Wisconsin's Department of Orthopedics & Rehabilitation and Biomedical Engineering. In addition to his research, Heidersheit directs a runners clinic and participates in half-marathons and triathlons. He has a half-marathon best of 1:38.
Stride Changes As Runners Maintain Speed But Alter Stride Length
- 10 % STRIDE RATE NORMAL STRIDE + 10 % STRIDE RATE
Stride Length (cm) 111.8 100.8 91.9
Center Mass "Bounce" (cm) 10.7 8.7 7.0
Contact to Cent Mass (cm) 11.4 9.2 7.0
Braking Force (N/kg) 382 306 256
Pk Grnd React Force (N/kg) 24.2 23.6 23.0
Enrgy Absrbd Knee (J/kg) 13.5 9.2 6.1
Runner's World: How did you get involved in the study of running biomechanics?
Bryan Heidersheit: I've been doing research in the area for 15 years, started running about 10 years ago, and have worked with our Runners Clinic for the last 8 to 10 years. I wish I could say I was smart enough to say I came up with the idea for this current study, but the first thought came from the runners we work with. We heard a number of them say that their knee-injuries didn't bother them when they ran fast. That didn't make much sense at first, since faster running increases all the forces of running, but then we began thinking about what else happens when runners go fast. For one thing, they often increase their stride rate, which could decrease stride length. They might land a little different.
So we started suggesting that some of our patients with knee injuries run with a shorter stride. And many reported that their symptoms went away almost immediately.
To be clear, in your current study, you didn't ask your subjects to run in a particular kind of shoe or with a particular kind of running form, right? You just asked them to bring their usual shoes to the lab and to run in their normal way. So they probably all brought in their usual training shoes and ran in them?
That's exactly right.
And looking at your data, it appears that most of them landed on their heels.
I would say they landed on the rear part of the foot. They weren't necessarily coming down sharply on their heels. On observation, you'd say that many were landing quite softly on the rear part of the foot.
And you measured lots of changes in forces and motions when these runners shortened their strides. What would you say is the big take-home message for typical runners?
If they increase their step rate quite subtly–by about 5 to 10 percent, which reduces their stride length by the same–then they can substantially reduce the forces to their knees. That happens primarily because they're lowering the vertical displacement of their center of gravity [their "bounce"], and hence coming down more gently. They also reduce the distance between their foot landing and their center of gravity. This reduces braking forces. The forces absorbed at the hips are also lower with shorter strides.
Some people would argue that shorter strides require more landings per mile, and therefore could increase injury risks. Others argue that it's not the total strides but the impact transient, or loading rate, of the first 20 to 40 percent of the stride that is most important, and that this decreases with shorter strides. I guess you're in the second camp?
That's right. The only study we could find that measured injuries by loading rates found more tibial stress fractures when the loading rates were higher. For now, we believe a lower landing force helps runners because it's what they are reporting to us in the Runners Clinic. If we shorten their strides, a lot of their problems go away.
What do you think would have happened if the runners in your study had worn racing flats?
I'd guess, and this is just speculation, that they wouldn't run the same as in the training shoes. I think they would have selected a preferred stride rate close to our +5 percent condition.
Because the thinner soles would give them less protection, so they'd feel this and naturally run with shorter strides?
Do you think that thick, cushioned shoes lull runners into taking a too-long stride?
That seems a reasonable conclusion based on a number of studies, including Daniel Lieberman's work at Harvard. But it's also very individual. If you look at his video of some of the barefoot runners in his lab, some of them have long strides too and land on the rear foot, but not with a sharp heel landing. A lot of the big action happens at the very end of the stride. Some people fall forward onto their extended foot, while others begin to reverse their foot action before they put the foot down. Thicker shoes probably encourage runners to fall forward onto them.
There's a fair amount of interest among running-form fans on the topic of center of gravity, and whether or not it's possible to land under your center of gravity. What are your thoughts?
We talk a lot about that here too. I have a friend from the physics department here who's a very active runner, and he insists that it's absolutely impossible to land under your center of gravity and maintain your upright posture while running. I agree. When we look at videos of people who self-report that they're running under their center of gravity, the videos don't support them. The videos show them landing in front of their center of gravity.
When the runners in your study increased their stride rate by 10 percent, they reported a higher perceived exertion. That's not a good thing for someone who wants to run fast.
That's right. But we think this is probably the neuromuscular cost of adapting to a new running form. We believe it would fade away after two to three weeks of practicing the new form. It's easy to learn a faster stride with a metronome, but all our runners tell us it feels "goofy." It's a subtle difference that actually feels quite big at first–it feels short and choppy. We put them on a treadmill and video them to show them that they aren't running goofy at all. And when they see these videos, they agree that they're running in a normal way. Just with a faster stride.
Several decades ago, it was thought that runners naturally "optimized" their running form, and that maybe it was impossible to change running form anyway. That attitude seems to be changing.
Yes, it is. You have to remember that many of those early studies were done with elite runners. They might have been running 100 miles a week. If anyone was going to discover their optimal running form, it was those guys. But today at Runners Clinics we're dealing with runners in maybe their mid-30s who haven't done much exercise since college. They've gained weight, they've lost muscle, they've aged, and yet when they begin running, they fall back into their old habits from 10 or more years earlier. These are the people who often get injured, and they're also the ones who can benefit by reducing their stride rate.
There's a lot of advice out there for runners these days. Run barefoot. Run in minimalist shoes. Run on your forefeet. And now you're saying that running with a shorter stride achieves many of the same things. Are you prepared to say it's a better, smarter approach than the other alternatives?
We had a section in our paper that made that argument. But we dropped it. Actually we had lots of other results and sections that didn't fit into this paper. We hope to publish them soon in other papers. We decided against pushing the shorter strides harder at this point because we don't have good injury results yet. We hear the stories from our Runners Clinics, and we have results coming in. But we're not quite there yet.
Do we think that a shorter stride is maybe a simpler approach than some other ways? Sure. It can reduce the forces a lot, it can change your running posture a little, and it may reduce injuries. If you want to change your posture a little more, you could run in a shoe that's not as built-up at the heel as some other models. Running with a short stride could even be a good way to transition to barefoot running if that's what you want to do. It's a good first step. It will increase your cadence. It will change your landing posture. Then if you want to move on to barefoot running….
Is it possible that some of these changes you and various people are recommending will decrease some kinds of injuries but increase other injuries?
Sure, that's possible. We've shown that the big benefit is at the knees, and then the hips. The ankle forces don't change. I'm okay with that. The ankle isn't usually a problem for most runners. Yes, you could create more ankle and foot injuries for people whose tissues haven't adapted fully. But the big picture is, if you change the big forces by lowering the center of gravity displacement and lowering the landing impacts, I can't see how that can be a bad thing for any injury.