The automobile is a remarkable achievement of mechanics. But in the end, it鈥檚 got nothing on the human leg.
Rodger Kram, associate professor of integrative physiology at the University of Colorado Boulder
鈥淲ell, to walk and run we have to use all the same equipment. 鈥� (The leg) is an elegant device with an elegant structure that does all three things 鈥� motor, brake and bounce.鈥�
So what more natural field of inquiry for scientist-runners than the locomotion of humans and animals? Kram, a long-time runner, and Kristine Snyder, who earned her Ph.D. at CU-Boulder in 2011 and is now a post-doctoral researcher at the Neuromechanical Laboratory at the University of Michigan, aren鈥檛 content to merely admire muscles and tendons; they want to know how they work and how that information can be used to prevent injuries, develop prosthetics and more.
And in 鈥淭he role of elastic energy storage and recovery in downhill and uphill running,鈥� published this year in the Journal of Experimental Biology and co-written with CU Ph.D. graduate Jinger Gottschall of Pennsylvania State University, they wanted to gain a better understanding of how muscles and tendons 鈥� which store elastic energy in much the way a spring compresses and stretches 鈥� work together when runners get away from the flats.
鈥淚f you run here (in Boulder), you can鈥檛 help but be interested in going uphill and downhill,鈥� Kram says. 鈥淚t鈥檚 hard to avoid.鈥�
Using data collected from 15 healthy recreational athletes running on a treadmill, Snyder鈥檚 rigorous applied mathematical abilities, and her previous research on optimal stride frequency for runners, the study yielded results both expected and unexpected.
Snyder鈥檚 previous investigations of stride frequency 鈥� two steps, one by each foot 鈥� found that human bodies pretty much find their own natural frequency, in the range of 85 to 90 per minute.
鈥淪ome people have a fascination with steps, thinking you have to have 180 per minute. But you can just relax. You don鈥檛 have to think about what all the books say you should do when running uphill or downhill. Just do what comes naturally,鈥� Kram says.
And here鈥檚 the not-so-surprising news about running uphill: leg muscles have to perform more work from tendons when runners are going uphill. Tendons provide the spring or 鈥渂ounce鈥� runners have at their disposal when running on even ground (think photos of Jamaican sprinter Usain Bolt, both feet off the track), but muscles have to provide more 鈥渕otoring鈥� power on an incline.
Kristine Snyder, who earned her Ph.D. at CU-Boulder in 2011, is shown here running on the treadmill used to collect data from athletes.
On level ground, 鈥�42 percent of the total work for a given step is done with elastic energy,鈥� says Snyder, who ran cross country as an undergraduate at Bryn Mawr. On a grueling incline of 15.6 percent 鈥� equivalent to the steepest part of Boulder鈥檚 Flagstaff Road 鈥� that portion drops to 24 percent, indicating the increased work of muscles.
The results for downhill running provided some interesting insights, as well. But instead of acting as springs, leg muscles and tendons must act more like brakes and shock absorbers.
鈥淭hat鈥檚 why you get so sore when you go downhill. You are absorbing all that energy,鈥� Snyder says. Heading downward is less energetically 鈥渆xpensive鈥� than running on flats or uphill, requiring less muscle power.
But the researchers found that if the decline is less than about 10 percent, you have to use more muscle work, and if it鈥檚 more than about 15 percent, the effort of shock absorption makes increasing demands on energy.
鈥淭here is a kind of sweet spot. If you are running downhill, you want that kind of angle,鈥� Snyder says.
Hills, of course, may not be so obliging as to provide a sweet spot. But the research offers insights into everything from injury prevention to prosthetic design (CU鈥檚 Locomotion Lab was involved in several studies analyzing the performance of amputee athletes, including Olympic sprinter Oscar Pistorius, who use blade-like, carbon fiber leg prostheses in track events). Assistant research professor, Alena Grabowski is already working on developing a motor powered prosthetic ankle for running and walking uphill, Kram says.
鈥淢ost human prosthetics are designed for walking and a small subset are good for running on flat ground,鈥� he says. 鈥淎necdotally, users report that they are not good for uphill and downhill. 鈥� So we can apply the biomechanics of how biological legs walk and run on hills to making artificial legs.
To see a report noting Rodger Kram鈥檚 work related to Olympian Oscar Pistorius, click听.听