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, whereas those that are notably sturdy usually elevate 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.