Motivating mighty mitochondria

Health researchers have long known you don’t have to train like an Olympian to stave off obesity, diabetes, and the other diseases of sedentary lifestyles.

But it turns out you may not need to do all that much exercise at all, and more importantly, the benefits in improved health begin almost instantly. Even a single bout of moderate exercise, like tooling along the bike path for a few minutes, scientists have found, can be enough to produce important changes in how your cells function, significantly improving how they process fats and sugars.

In a paper in Medicine & Science in Sports & Exercise, Matthew Robinson, an exercise physiologist at Oregon State University, US, had 15 sedentary volunteers (11 women and four men) do a single one-hour session on a stationary bike at moderate intensity (defined as about 65% of maximum effort). To put this in perspective, that’s the pace at which they could easily keep up cycling for an hour, while still carrying on a normal conversation.

Robinson then biopsied the volunteers’ cycling muscles and extracted mitochondria from them to compare to ones taken when they hadn’t been exercising.

Mitochondria are the subcellular power plants that burn fuel to run our muscles.

In the body, they provide the energy that allows muscle fibres to contract, and in the lab, even after they are removed from these cells, they retain their function. That allows their efficiency to be tested by feeding them sugars and fats, and seeing how they perform.

In this case they performed surprisingly well. That single exercise bout, Robinson says, was enough to make them burn up 12–13% more fat, or 14–17% more sugar, depending on which they were given.

That’s not super dramatic – but it’s part of the explanation, he says, for why, after exercise, our bodies continue to burn off more energy, even when resting.

Not that it means the entire body is suddenly burning 12–17% more fat or sugar. More likely, it’s just the muscles most heavily involved in exercise, in this case, the legs. But still, Robinson says, “it’s pretty remarkable that even after just one hour of exercise, these people were able to burn off a little more fuel.”

Prior studies had shown that exercise increases the metabolic rate, but that could be linked to any of a number of factors, including increased blood flow and the movement of nutrients from the blood into muscle cells. “What we found is that we got these small but consistent changes within the mitochondria themselves,” Robinson says. “This is an increase in how much they use, just sitting there.”

One benefit of such an increase in metabolic rate is that it can help stave off obesity. But it should also help fight off diabetes.

“The leading hypotheses right now are that there is some alteration with a sedentary lifestyle or obesity that causes fats to accumulate [inside muscle cells] and impair insulin action,” Robinson says. If so, anything that causes mitochondria to burn off these fats rather than letting them accumulate is beneficial. “It’s clear,” he adds, “that exercise is a potent way that we could reduce type II diabetes.”

There are, of course, lots of caveats. For example, Robinson’s study subjects were sedentary but not off-the-charts out of shape. Most were normal weight or, at most, slightly overweight. Fitness tests found the women to be in the lower one-third, overall, and the men to be in the bottom 10%. That’s poor, but not so bad they couldn’t spend an hour on a bike.

They were also relatively young (average age 28). That’s potentially relevant for people who are older and/or further out of shape, says Kelly Scott, a primary-care physician in Portland, Oregon. “[I’m] not sure how many of my middle-aged or old sedentary folks could get to an hour of moderate-intensity exercise,” she says.

But, she notes, maybe you don’t have to go all the way to an hour – or all the way to “moderate” intensity to start getting a benefit. “Those mitochondria are amazing,” she says, and “[just] knowing that it really works should be a motivator.”

Robinson agrees. “From a big-picture health perspective, it’s very encouraging for people to realise that you can get health benefits from a single session of exercise,” he says.

Not that the benefits of a single such workout are permanent. The body easily relapses to its pre-workout state – probably in three to four days. But Robinson says all that’s needed to prevent this is to not rest too long on your laurels. “We’re trying to encourage people: ‘You did one [day of exercise], why don’t you do two?’ [Then] ‘Let’s do three.’ If we do this again and again, these small changes could have some pretty large impacts,” he says.

All of which is not all that surprising, says Daniel Lieberman, an evolutionary biologist and exercise researcher at Harvard University, Massachusetts, whose latest book, Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding, examines, among other things, the role of exercise in the world’s few remaining hunter/gatherer cultures.

“We never evolved to be couch potatoes,” he says. “So, even a little physical activity turns on normal processes that lead to ‘normal’ benefits.”