Science of Running

Post-run calorie burn

We all know that running burns calories. But what about after you stop: does your metabolism stay revved up and continue burning extra calories? This hypothetical “afterburn” effect has been the Yeti of exercise science for years, frequently discussed but never confirmed – until now. The new North Carolina Research Campus includes a high-tech metabolic chamber that allows researchers to precisely determine to number of calories burned by subjects inside. It monitors the gases flowing in and out. Researchers asked 10 men to spend two 24-hour periods in the chamber: one where they did basically nothing, and the other where they did nothing except one 45-minute cycling session at about 80 percent of max heart rate.

The results were clear: exercise boosted metabolism for 14 hours after the cycling session, even after the subjects had gone to sleep. In total, they burned an average of 190 extra calories – a 37-per cent bonus on top of the 519 calories they burned while cycling. One of the keys, according to lead researcher David Nieman of Appalachian State University, is that the cycling was fairly vigorous: “enough to make you work up a good sweat.” In contrast, some earlier studies that failed to detect an afterburn effect used more leisurely exercise protocols. The bottom line: a hard workout can keep the furnace burning hotter for the rest of the day.

Intervals and insulin

“High-intensity interval training” (HIT) has been a big buzzword in exercise science over the past few years, with studies showing that short, intense bursts of exercise can produce many of the same benefits as long, steady cardio sessions. But the protocol used in many studies – 30-second all-out sprints followed by long rests – is very challenging for inexperienced exercisers. Martin Gibala and his colleagues at McMaster University have been testing a protocol that is easier for most runners to adopt: 10 x 60 seconds hard, with 60 seconds of recovery between each interval – a workout that’s very similar to the one Roger Bannister used on his way to breaking the four-minute-mile barrier.

The latest study from Gibala’s group, published in Medicine & Science in Sports & Exercise, confirms that this protocol is effective for sedentary, middle-aged subjects – not just the active university students who typically volunteer for these studies. After only two weeks, with three HIT workouts per week, the subjects in the latest study had improved their insulin sensitivity by 35 per cent – a major boost in the battle against conditions like metabolic syndrome. It’s confirmation of what runners have known since Bannister’s era: mixing a couple of interval sessions into your weekly schedule trumps a steady diet of long, slow runs.

Digestive matters

There’s no delicate way to say this, so let’s cut straight to the point: a study of elite Swedish orienteers found that during heavy training (running one to two hours per day), they had more bowel movements than during rest weeks (1.5 per day versus 1.3). Their stools were also looser: 4.2 versus 3.9 on the Bristol Stool Form Scale, which rates stools from a hard, “nut-like” 1 to a watery 7. The findings are (perhaps uncomfortably) familiar to many runners – but what does it mean? A detailed analysis, published in the Scandinavian Journal of Gastroenterology, found that food left the stomach at the same rate during heavy training. It then travelled more rapidly through the small intestine, where most nutrient absorption takes place, but spent the same amount of time in the large intestine. Unfortunately, the researchers didn’t reach any conclusions about how to avoid these effects. The best advice is still to pay attention to how different foods affect your digestion, and reduce your pre-run fibre intake if you’re drifting too high on the Bristol Scale.

Mitochondrial aging

Scientists don’t know exactly why or how we get old, but they have a few theories. One of them is that mutations in mitochondrial DNA gradually accumulate until body systems stop working properly – a theory supported by the premature aging observed in mice genetically engineered to rapidly accumulate mutations in mitochondrial DNA. New research from McMaster University’s Mark Tarnopolsky, published in the Proceedings of the National Academy of Sciences, found that this aging process could be halted by – you guessed it – running. In mice programmed with the DNA defect, those who ran three times a week “looked as young as healthy mice, while their sedentary siblings were balding, greying, physically inactive, socially isolated and less fertile,” the researcher reported.

And the changes weren’t just on the outside. The brains of the runner mice didn’t shrink, their muscles didn’t waste, their hearts didn’t weaken, and they didn’t die prematurely. Overall, the effects were startling, especially compared to previous experiments that had attempted to halt aging in the genetically engineered mice using drugs or calorie restriction. “Many people falsely believe that the benefits of exercise will be found in a pill,” said Tarnopolsky, himself an accomplished ultrarunner. “We have clearly shown that there is no substitute for the ‘real thing’ of exercise when it comes to protection from aging.”

Beet boost

A series of experiments in the past two years has turned beet juice into one of the hottest endurance-boosters among elite athletes. Studies suggest that, after a big blast of beets, your muscles don’t need as much oxygen to contract, allowing you run up to 15 per cent farther before reaching exhaustion. A typical dose: 500 ml a day for four days before a race. Now a study from researchers at Sweden’s Karolinska Institute sheds some light on how it works: the nitrates in beet juice (which are also found in leafy green vegetables) appear to help mitochondria in your cells general ATP – the chemical fuel that powers your muscles – more efficiently using less oxygen.

But there’s an unexpected twist. In order to work its magic, the nitrate first needs to be converted to a related molecule called nitrite. Our bodies can’t do that on their own – it’s actually friendly bacteria in our saliva that performs the conversion. Another experiment by the same Swedish group found that gargling with an antibacterial mouthwash killed the bacteria and prevented them from converting nitrate to nitrite. For now, these results remain preliminary: it’s not clear whether rinsing with mouthwash at night affects your ability to convert nitrate to nitrite the next day. But it raises the possibility of a new pre-race ritual among those who are truly dedicated to fast times: swearing off mouthwash for the week before a race.

Alex Hutchinson is a senior editor with Canadian Running.