The Best Type of Exercise? A Blood Test Holds Clues

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.

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