Stride length and stress fractures

With every step you take, your bones feel a jarring impact that over time can lead to a stress fracture. If you shorten your stride, each impact will be a little gentler, but you’ll have to take more steps to cover a given distance – so it’s not clear whether that would help or hurt you. Researchers from Iowa State University tackled this question in the latest issue of Medicine & Science in Sports & Exercise, using high-speed cameras and force-sensitive platforms to analyze the running motion of 10 volunteers. By calculating the forces involved, they estimate that reducing stride length by 10 per cent does, in fact, decreases the probability of stress fracture by three to six per cent.

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Of course, messing with your stride length isn’t something to be done lightly. Some studies have found that most elite runners, whatever their height and leg length, take about 180 steps a minute, while less accomplished runners often take 165 to 175. As a result, they suggest doing “strides” – short, relaxed sprints – a few times a week to help increase turnover. On the other hand, a 2007 study in the European Journal of Applied Physiology found that runners naturally select the most efficient stride rate for their body, and any changes just make things worse. The safe middle ground: do strides and other drills that help turnover, but don’t turn your everyday runs into stride-counting nightmares.

It’s easier in groups

Running always seems easier when you’re surrounded by a group of like-minded souls. The conversation is one benefit, but a new study in Biology Letters suggests that there may be something deeper going on. Researchers from the University of Oxford had members of the school’s vaunted rowing team perform two identical 45-minute rowing workouts in a “virtual boat” in a gym. In one trial, the subjects rowed with five other teammates; in the second, they rowed alone, but at the exact same level of exertion. Afterwards, the researchers wrapped a blood-pressure cuff around the rowers’ arms and tightened until the pain was too much to take. The subjects were able to tolerate twice as much pain after group training compared to the solo session.

Pain tolerance, in this case, was used as an indirect measure of endorphin production. The researchers speculate that we may have evolved to experience pleasure from group activities because behaviour such as group hunting is favourable to the survival of the species. As a result, they suggest, the endorphin-fuelled pleasure we get from group activities may underlie our attachment to things like dancing, sports and religious rituals. And, we might add, the Sunday-morning group run.

Don’t focus on your breathing

Beginning runners are often told to focus on their breathing, for instance by inhaling and exhaling after a certain number of steps. A study in the Journal of Sports Sciences by researchers at the University of Münster in Germany put this advice to the test, by examining runners while they focused on either their breathing, their running form or their surroundings. Running economy – a measure of how much oxygen it takes to run at a certain speed, which is generally thought to be something we can’t consciously control – was worst in the breathing group and best in the group focused on their surroundings. The very act of focusing on breathing caused runners to unconsciously slow from about 37 breaths a minute down to 30 breaths a minute, resulting in deeper but less efficient respiration.

The study joins others that have found that once we learn complex actions like throwing a dart or putting a golf ball, we do better on “autopilot” than focusing on the motion. With running, though, it’s not so clear, because other studies have found that racers do better when they “associate,” focusing on their task rather than letting their mind wander. The difference may have to do with pace: in this study, the subjects were running at 75 per cent of VO2max, which corresponds to a brisk training run rather than a race. So further research is needed – but until then, don’t count your breaths too closely.

Neural coupling

“Keep pumping your arms!” That’s one of those standard pieces of advice offered by just about every coach. The idea is that, late in a run or race when your legs are burning and you’re starting to slow down, if you keep moving your arms briskly, your legs will follow. Whether or not this actually works is hard to say – but research by biomechanists at the University of Michigan offers some tantalizing hints of why it just might. A movement scientist named Daniel Ferris has been studying methods of rehabilitation for patients with spinal cord injuries, and he believes that having the subjects swing their arms may help them relearn to walk. In a study that appeared in the journal Exercise and Sport Science Reviews, Ferris and his colleagues strapped subjects in a “recumbent stepper” that allowed them to exercise with their arms, legs, or both. The subjects were consistently able to exert more force with their legs if they were moving their arms in sync, a phenomenon Ferris attributes to “neural coupling” between the arms and legs. Whether this same effect can help boost your finishing kick is an open question – but it’s worth a try.

Hard and soft surfaces

Most runners would agree that pounding the pavement feels different than galloping on grass. How different? Well, a new study in the Journal of Science and Medicine in Sport suggests that your feet feel about 12 per cent more pressure with each footstrike on asphalt compared to grass. Vitor Tessutti and his colleagues at the University of Sao Paulo used a shoe insert with about 100 pressure sensors to measure the forces produced. Surprisingly, this result conflicts with previous studies that have found the forces are roughly the same. Those studies suggested that when the hardness of the running surface varies, runners adjust the effective stiffness of their legs in the opposite direction – by bending their knees slightly more or less and by tensing their muscles – so that their total up-and-down motion remains perfectly constant.

A bigger factor may be the smoothness of the surface. Paved surfaces are very regular, so each foot strike sends exactly the same forces up through the skeleton, muscles and tendons. Irregular surfaces like grass and dirt, on the other hand, produce minor variations that spread the stresses out – though if they’re too irregular, there’s the risk of turning an ankle. But in terms of pounding, the new Brazilian study tells us that, while our feet feel really do feel a difference between surfaces, it’s probably smaller than we thought.


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