The Science of Running

Save your knees

It’s a warning every runner has heard: “You’re going to ruin your knees if you keep doing all that running.” As unsolicited advice, it’s a bit annoying (especially when it comes from a guy sitting on his porch smoking a cigarette as you jog by). But even though several studies have failed to find any evidence of short-term or medium-term damage, it’s hard not to wonder whether there might be something to the warnings, given the aches and pains that pounding the pavement sometimes produces.

A newly published study by a group of radiologists and orthopedic specialists in Vienna now gives us the first long-term look at running’s effect on the knees. Eight runners were given MRI scans before and after the 1997 Vienna marathon, then reexamined in 2007 (when their average age was 50) to determine the effect of a decade of running. The results, which appear in the journal Skeletal Radiology, are encouraging. No significant new internal damage was found in the knee joints of the seven subjects who had continued running over those 10 years. “In contrast,” the authors note, “the only person who had given up long-distance running showed severe deterioration in the intra-articular structures of his knee.”

It’s important that we don’t get carried away in drawing conclusions from such a small study. As Ottawa Hospital radiologist Matt McInnes, a two-time Canadian marathon champion, points out, there’s also the question of selection bias: “These runners stayed in the sport long enough to be able to run a full marathon, so runners who weren’t able to get that far because of degenerative changes may have been excluded,” he says. But overall, the study is good news – especially in contrast to research reported in May by the American College of Sports Medicine showing that each additional pound of body weight places an additional four pounds of stress on the knee. As a result, packing on about a pound a year for a decade causes a 50 per cent increase in the likelihood of developing osteoarthritis. So if you don’t want to ruin your knees, keep on running.

Treadmill vs. road

There’s a long-standing riddle about whether an airplane on a giant treadmill would be able to take off, and the endless arguments it inspires show that we’re a little hazy about how physical laws apply when the ground is moving. Runners (and scientists) have a similar debate about the how running on a treadmill affects your stride and effort level. In theory, the only difference between running on a treadmill and running on a flat road is the lack of wind resistance on the treadmill, which some coaches suggest compensating for by adjusting the treadmill to a one per cent incline. That’s a little simplistic, since the effect of wind resistance depends on how fast you’re running – and is all but irrelevant if you’re going slower than about 4:00 per kilometre.

But there are some more subtle factors at play, relating to the fact that you’re no longer choosing the speed you move at. A study in the most recent issue of Medicine & Science in Sports & Exercise takes a detailed look at the kinetics (the joint angles and body orientation) and kinematics (the forces on and power produced by each joint) of treadmill running compared to “overground” running. The researchers found that the parameters were “comparable but not directly equivalent” in the two cases. For instance, at the same speed, treadmill runners take slightly shorter, quicker strides (they averaged 175 strides per minute compared to 170 for the overground case). There were also minor differences in knee angle, and in the propulsive force produced.

The differences were attributed to factors like the slightly softer surface of the treadmill belt, and the fact that no treadmill is capable of maintaining a perfectly steady speed. The scientists were most interested in figuring out whether biomechanics and exercise physiology studies conducted on treadmills can be applied to real life – and they concluded that, with a good-quality, well-maintained treadmill, they can. That doesn’t mean that training on the treadmill is exactly equivalent to training outdoors. If you want to run a 5K race, you should be accustomed to running on slightly uneven surfaces and setting your own pace. But, when the roads are iced up this winter, you can be confident that the basic motions are pretty much the same. (And, for the record, under the right conditions the plane can take off from the treadmill.)

Interval training

Runners already know that one of the best ways to get faster is to incorporate interval workouts into their training: short, sharp bursts of speed separated by periods of rest. In the past few years, there’s been an increasing pile of evidence that interval training is also a very time-efficient way of getting the same health benefits you might get from long periods of less intense training. A recent study from McMaster University – a leader in this field – adds the news that interval training improves heart health. The study compared subjects doing four to six all-out sprints for 30 seconds on an exercise bike three times a week, to control-subjects doing 40 to 60 minutes of biking five times a week. The improvement in the structure and function of crucial arteries that deliver blood to the muscles and heart was the same in both groups.

Maximal strength training

A Norwegian study had a group of distance runners do eight weeks of “maximal strength training” for their lower body, consisting of four sets of half-squats with the weight chosen so they could just barely complete four repetitions per set, three times a week. Aside from the expected strength gains, the runners improved their running economy (a measure of how much energy it takes to run at a given speed) by five per cent, and as a result were able to maintain their maximal aerobic speed for 21 per cent longer. Interestingly, they didn’t add any muscle mass, so the gains came primarily from improved neural recruitment: when the brain says “contract,” the muscles do a better job of responding. Bottom line: the traditional dogma for distance runners – low weights and lots of repetitions to avoid putting on too much muscle mass – may be not be the whole story.