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How Weight Affects Your Race Times

How Weight Affects Your Race Times

The weight of your shoes, as well as your body weight, influence your race performances. Here’s how much they change your finish time.

Weight matters in running. Shave a few grams off your shoes or kilos off your body, and you’ll likely run faster. A new paper from Rodger Kram’s highly regarded biomechanics lab at the University of Colorado, USA, adds to our understanding of weight, running economy and race performance.

In the study, researchers first had to trick their way, literally, through a knotty protocol problem. How do you conduct a study when subjects can easily tell whether they’re wearing sleek racing flats or heavier training shoes? To solve this issue, first author Wouter Hoogkamer brought in a U.S. Olympic steeplechaser.

Shalaya Kipp won the National Collegiate Athletic Association (NCAA) steeplechase title in 2012, and then went on to compete in the London Olympics. She was fourth in the steeplechase at the U.S. Olympic Trials this year. She’s currently pursuing a master’s degree at Colorado after studying psychology and integrative physiology as an undergrad. Hoogkamer thought her running and psychology background could help Kipp design a “deception procedure” for his light versus heavy shoes conundrum.

It did. In their experiment, Hoogkamer, Kipp, and colleagues used identical-looking pairs of 153 gram Nike Zoom Streak 5 shoes. Identical looking…but then came the deception. Some of the shoes had 100-gram weights sewn into the tongue and side pockets, and some had an additional 300 grams on board.

Because subjects might have felt these weights while pulling on the shoes and lacing them, this was forbidden. Subjects never touched the shoes. The researchers did all the pulling on and lacing up.

The deception worked. Only one of the 18 male subjects (all with 5K bests under 20 minutes) perceived any difference in shoe weights. He was tipped off when he noticed the wider lace-up pattern of the heavier shoes.

In the actual running economy and performance testing, all subjects ran three separate 3000-metre time trials on Colorado’s indoor track – one in the unweighted shoes, one in the +100 gram shoes, and one in the +300 gram shoes. The results: running economy varied by about 1 per cent per 100 grams, as did running performance. This was the first fully subject-blinded trial of shoe weights and performance outcomes.

The results also agreed closely with prior, less deceptive studies. Therefore, Hoogkamer told Runner’s World: “Changes in running economy with shoe mass have been consistent in several high-quality papers. I think it’s fair to round off to about 1 per cent change in performance per 100 grams of shoe mass.”

Many popular training shoes weigh about 250 grams. Racing flats check in at around 150 grams. So switching from one to the other on race day should theoretically improve your finish time by 1 per cent. That changes a half marathon time of 2:00 to a 1:58:45.

But theory doesn’t always win out in practice. A recent study in the Colorado lab as well as papers stretching back to the early 1980s indicate that a modest amount of midsole cushioning may improve performance in marathon and ultra-marathon races. This occurs even though the cushioning also adds weight to the shoes. Researchers believe that, in this situation, more cushioning decreases muscle breakdown and fatigue, leading to better finish times.

Many runners realise that losing a few kilos will probably enhance their racing. But how much? Hoogkamer cautions that this is a complex calculation that should include, among other things, initial body weight, and percent of overall muscle and fat loss. It’s not a good idea to lose weight if you are already in top shape, and it’s also bad if you lose muscle instead of fat.

That said, runners with excess fat could improve their times as much as one percent for every 500g they lose. That is, if a 90kg man loses 4.5kg (five per cent), he should be able to race five per cent faster. A half marathon in 2:00 becomes a 1:54.

For physics fans, it’s interesting to note that losing body weight is only about 30 per cent as effective as losing shoe weight. That’s because extra weight on your shoes requires a great deal of energy to accelerate each time you stride forward. Whereas weight around the middle and upper body gets a relatively free ride.

On the other hand, there’s not much you can do about your shoe weight, especially if you’re running in light shoes to begin with. Your body weight, however, is subject to potentially large changes.

 

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