What is the best type of exercise?

Publish: 9:37 PM, June 19, 2021 | Update: 9:37:PM, June 19, 2021

Gretchen Reynolds
If we all begin the same exercise routine tomorrow, some of us will become much fitter, others will get a little more in shape, and a few of us may actually lose fitness. Individual responses to exercise can vary that wildly and, until now, unpredictably. But a fascinating new study of more than 650 men and women suggests that the levels of certain proteins in our bloodstreams might foretell whether and how we will respond to various exercise regimens.

The study needs replication and expansion, but represents a meaningful start toward a blood test to indicate the best types of exercise for each of us, and if we can expect to gain more or less benefit from the same workout as our spouse, offspring or other training partners or rivals.

Exercise response is a topic that probably should be discussed more often and openly than it is. We know exercise is wonderful for our health. Countless studies show that people who exercise tend to live longer, more happily and with less risk of many diseases than sedentary people. But those findings refer to broad averages. Parse the study data closely and you can find a dizzying gamut of reactions, from outsized health and fitness gains in some people to none in others. (The same is true of responses to weight-loss programs.)

Disobligingly, little about our bodies and lives currently predicts how we will respond to exercise, including our genetics. Identical twins, with identical DNA, can react quite differently to workouts, studies show, as can people who are equally lean, obese or aerobically fit at the start of a new exercise program. Some, for mysterious reasons, wind up fitter and healthier afterward than others.

These enigmas intrigued researchers from Harvard University, the Beth Israel Deaconess Medical Center in Boston, and other institutions. The scientists had long been interested in how exercise alters the molecular environment inside the body, as well as how those changes influence health, and how diverse the alterations can be.

Now, for the new study, which was published in May in Nature Metabolism, they decided to see if certain molecules in people’s blood might be related to how their physiologies react to workouts. To find out, they turned first to the valuable trove of data produced during the large-scale Heritage study, which had delved into exercise and health in parents and their adult offspring. The Heritage study included precise, laboratory testing of people’s aerobic fitness, as well as blood draws, followed by 20 weeks of moderate aerobic exercise, and more testing.

The researchers now pulled records for 654 of the men and women who had participated in Heritage, covering a range of ages and ethnicities, and began looking deeply into their blood. They focused on the varieties of large, complex protein molecules created in tissues throughout the body that, when released into the bloodstream, flow to and jump-start biological processes elsewhere, affecting how well our bodies work.

Using state-of-the-art molecular tools, the scientists began enumerating the numbers and types of thousands of proteins in each of the 654 people’s bloodstreams. Then they tabulated those figures with data about everyone’s aerobic fitness before and after their five months of exercise.

And clear patterns emerged. The levels of 147 proteins were strongly associated with people’s baseline fitness, the researchers found. If some of those protein numbers were high and others low, the resulting molecular profiles indicated how fit someone was.

More intriguing, a separate set of 102 proteins tended to predict people’s physical responses to exercise. Higher and lower levels of these molecules – few of which overlapped with the proteins related to people’s baseline fitness – prophesied the extent to which someone’s aerobic capacity would increase, if at all, with exercise.

Finally, because aerobic fitness is so strongly linked to longevity, the scientists crosschecked levels of the various fitness-related proteins in the blood of people enrolled in a separate health study that included mortality records, and found that protein signatures implying lower or greater fitness response likewise signified shorter or longer lives.

Taken as a whole, the new study’s results suggest that “molecular profiling tools might help to tailor” exercise plans, said Dr. Robert Gerszten, a professor of medicine at Harvard Medical School and chief of cardiovascular medicine at Beth Israel Deaconess Medical Center, who conducted the new study with its lead author, Dr. Jeremy Robbins, and others.

Someone whose bloodstream protein signature suggests he or she might gain little fitness from a standard, moderate walking, cycling or swimming routine, for instance, might be nudged toward higher-intensity workouts or resistance training, Dr. Gerszten said.

This area of research is still in its infancy, though, he and Dr. Robbins said. Scientists will need to study far more people, with far broader disparities in their health, fitness, age and lifestyle, to zero in on which proteins matter most for predicting an individual’s exercise response. The researchers hope, too, to backtrack and find where those molecules originated, to better understand how exercise remakes our bodies and molds our health. Expect further and more-refined results within a few years, Dr. Gerszten said.