NEW YORK (NYTIMES) - Riding or running before you lift weights could amplify the effects of the lifting, according to a new study of the molecular impacts of combining endurance and resistance exercise in a single workout.
The study, which involved eight physically active men, found that 20 minutes of intense cycling right before an upper-body weight routine alters the inner workings of muscles, priming them to change and grow more than with lifting alone.
The new paper, published in Scientific Reports, offers practical guidance about how you might structure a gym workout for maximal benefit. It is also a bracing reminder of how potent and wide-ranging the effects of exercise may be.
For decades, trainers and scientists have debated whether and how to mix cardio and resistance exercise. Some small studies suggest combining the two might up the likely gains from each, especially the resistance training. (Almost all of these experiments have been conducted in men.) But other research indicates sweaty aerobic workouts beforehand could reduce strength improvements from lifting.
The authors of some of these studies speculate that molecular changes within muscles, caused by riding or running, wind up hindering some of the other desirable outcomes from lifting, an effect called exercise interference.
Muscle fatigue might also play a role since in most studies that pair cardio and resistance, volunteers exercise only their lower bodies, using their legs both for the endurance and strength training. Tired from the endurance work, the thinking goes, their leg muscles could have become unable to respond ideally to resistance training.
But what if the two types of exercise targeted completely separate groups of muscles, such as legs during the cycling and arms during the weight routine? That was the scenario posed by Swedish School of Sport and Health Sciences' Professor Marcus Moberg, who studies muscle health, exercise and metabolism.
In that case, would the lower-body endurance exercise augment the benefits of the upper-body weight training? Or would exerting your legs and lungs have zero - or even an unwelcome, counterproductive - impact on the muscles in your arms?
To learn more, he and his collaborators recruited eight active adult men in Stockholm and invited them to the laboratory for measures of their current aerobic fitness and strength. Then, after the men had familiarised themselves with the lab's workout equipment, the researchers asked them, on a separate visit, to complete a two-part workout.
The men began with intense interval cycling. During this endurance exercise, the men pedalled hard for four minutes, rested for three and repeated that sequence five times. After a few minutes of rest, they next moved on to upper-body weight machines that strenuously worked their arm and shoulder muscles.
During a different lab visit, the men completed the same weight routine, but with no cycling first.
The researchers drew blood and took tiny tissue samples from the men's triceps muscles before, immediately after, 90 minutes later and then three hours after each workout. (The primary reason women were not included in the study, Dr Moberg said, was that women's less-developed triceps muscles make such repeated biopsies difficult and possibly injurious.)
Finally, the scientists microscopically examined the men's blood and muscle samples, looking for substances that indicated how their muscles were responding to the workouts, with special emphasis on proteins and markers of gene activity believed to influence endurance and muscle mass.
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 pedalling with their legs had not tired their arms.
"The paper is great," said Dr Michael Joyner, a physiologist and anaesthesiologist at the Mayo Clinic in Rochester 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 afterwards. 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 overall, 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.