They found them. After their solo weight training session, the men’s muscles teemed with proteins and genetic markers known to help initiate muscle growth. Those same substances also abounded after the workout that included cycling but were joined by other proteins and gene activity associated with improved endurance.
In effect, after the dual workout, the men’s muscles seemed primed to increase in both size and stamina, with no evidence that cycling had interfered, at a molecular level, with lifting. Instead, the aerobic exercise appeared to have broadened and intensified the expected benefits from weight training.
“The most fascinating finding is that some biochemical factors evoked by the leg endurance exercise entered the bloodstream and were then able to influence processes in a completely different group of muscles, and in a way that seems to be beneficial for the training adaptations in the arms,” Dr. Moberg said. “It is almost like the endurance exercise performed by the legs was being transferred to some degree to the arms.”
He pointed out, too, that the men lifted the same amount of weight during both arm workouts. Hard pedaling with their legs had not tired their arms.
“The paper is great,” said Dr. Michael Joyner, a physiologist and anesthesiologist at the Mayo Clinic in Rochester, Minn, who was not involved in the study. Its finding, he added, that “legs might have primed greater activation of key molecular pathways in the arms is a real piece of brain candy.”
Of course, this study, like so many similar experiments, involved only men. “But there is no good rationale for believing the effects would be any different in women,” Dr. Moberg said, adding he and his colleagues hope to include women in upcoming experiments with fewer biopsies. This study also was short term and looked at endurance exercise preceding weight training, and not the reverse. Some past experiments suggest lifting first has little impact, for better or worse, on aerobic exercise afterward. But those studies focused on legs, so it remains to be seen if working your arms before cardio can be as worthwhile as the other way around.
But over all, the upshot of the findings, Dr. Moberg said, is that starting a workout by exercising your legs and lungs before moving to upper body lifting makes practical and physiological sense. “It can be a time-effective and potentially beneficial approach,” he said.