Stamina may trump strength for improving metabolic health, according to an interesting and provocative new study of the molecular effects of different aspects of fitness. The study, which was published in August in JAMA Network Open, finds that people’s aerobic endurance — or lack of it — can influence their metabolisms more potently than their muscular weakness or might, a result with implications for anyone wondering which types of exercise could be most beneficial for health.
Our metabolisms are, of course, massively complex, encompassing the myriad biochemical reactions that transform calories into energy and keep our cells nourished. But many standard measures of metabolic health, such as blood sugar or cholesterol levels, are broad, providing an overview of the state of our interiors, but little detail.
So, in recent years, a new field of science, called metabolomics, has begun trying to better parse our metabolisms by using high-tech tools to enumerate the metabolites in our tissues. Metabolites are any molecules involved in metabolic reactions and include everything from proteins and fatty acids to minute, sub-particles of different forms of cholesterol.
By comparing the types, amounts, ratios and interactions of all of the metabolites in the blood of people with or without conditions such as heart disease, metabolomics researchers have been developing granular schematics of desirable — and detrimental — metabolite patterns. These molecular “signatures” of metabolic diseases eventually should help researchers to better diagnose metabolic problems and start teasing out how, at this molecular level, people’s metabolisms can be reshaped by nutrition or obesity or other issues.
Much of the original metabolomics research centered on illness, however, prompting some scientists recently to wonder about the blood signatures of sturdy good health and, in particular, of fitness. Fit people tend to have much lower risks for metabolic problems than the inactive. But whether that fitness is reflected in the patterns of metabolites in their blood and, if so, what those patterns might tell us about how physical activity molds metabolisms, remained largely unknown.
So, recently a group of Scandinavian researchers set out to learn more. First, for a study published in 2013, they compared the many metabolites in the bloodstreams of twins and other, unrelated adults, most of whose lives differed wildly in terms of how much they worked out. In the process, the scientists uncovered multiple and consistent differences between the bloodstreams of the active and sedentary men and women.
The people who often exercised almost all had elevated levels of certain particles of their high-density lipoprotein, which is the “good” cholesterol, and desirable ratios of specialized proteins that recently have been identified as important for heart health.
Together, these findings suggested that physical activity was affecting people’s metabolic health by rejiggering a few key components of their metabolomes.
But that study looked at physical activity monolithically, asking people only how often they moved. It was not designed to tease out whether different activities might affect molecular signatures differently, an issue that would matter if metabolomics were to be used to advise people about exercising for health.
So, for the new study, some of the original researchers decided now to focus on endurance and strength. These are the most fundamental elements of fitness and also provide insights into how people exercise. People with high endurance tend to run or cycle, while those who are notably strong often lift weights.
For their data, the researchers turned to a handy trove of records from the performance testing of 580 young Finnish men called up for military training. The men rode stationary bicycles and heaved weights to measure their maximum aerobic capacity and muscular strength. They also gave blood, completed general health testing and filled out questionnaires about their lifestyles and exercise routines.
Using this information, the researchers grouped the men. One group focused on the men’s aerobic capacity and stratified them from most aerobically fit to least. A second group ranked the men based on their strength testing, from strongest to weakest. Each man appeared in both groups, but with different rankings.
The scientists then checked the men’s blood for metabolites and, finally, compared metabolic readouts between the men in the top third and bottom third of the two groups. In other words, they assessed the metabolomes of the aerobically fittest men against those who were out of shape, and, separately, the strongest against their opposite.
(Some men appeared in both analyses, but, each time, the researchers looked only at their stamina or strength.)
The disparities the researchers found were telling. The men at the top in aerobic fitness harbored the same desirable molecular signature the scientists had found in their earlier study, with high levels of certain particles of good cholesterol and healthy ratios of proteins and fatty acids.
The blood of the men who were out of shape displayed different metabolites. In fact, about two-thirds of their molecules varied in type, amount or ratios from those of the fittest men.
But there were few differences overall in the metabolite profiles of the strongest men and those who were relatively weak.
These results, which generally held true when the scientists controlled for body composition, exercise habits and other factors, suggest that aerobic capacity affects metabolism substantially more than muscular strength does, says Dr. Urho Kujala, a professor of medicine and sports science at the University of Jyvaskyla in Finland, who led this and the earlier research.
In essence, “our study supports the idea that aerobic, endurance-type physical activity is good” for metabolic health, Kujala says.
Or, in practical terms, it hints that running may outmuscle weights, if you are concerned about your metabolic health.
The research involved only healthy, young, male Finns, though, and does not show that endurance changed people’s metabolomes, but only that their fitness and metabolites were linked.