Muscles are comprised of an intricate system of fibers, sending messages to the brain at every twitch or flexing movement. According to a team of researchers from the University of Kansas, how quickly muscles communicate with the brains’ is dependent upon the type of athletic training. The team's findings, published in the Journal of Sports Sciences and Muscle and Nerve, suggest the body may be designed to handle running better than strength training.

In order to figure out the speed of muscle-to-brain communication, researchers first placed electrode sensors on the quadricep muscles located on the thighs of 15 participants. Five of the participants were endurance runners who ran an average of 61 miles a week, but did not engage in any resistance training; this training is also known as strength or weight training. Another five of the participants were resistance trainers who lifted weights 4 to 8 hours each week and were strong enough to back squat twice their body weight. None of the resistance trainers, however, engaged in any type of aerobic activity, including running, swimming, or cycling. The remaining five participants lived a sedentary lifestyle and did not take part in any physical exercise for at least three years leading up to the study.

Once hooked up to the electrodes, each participant was asked to extend their leg forward and contract their thigh muscle with 40 to 70 percent of force so researchers could see how quickly each person performed in real time. It turned out the runners’ muscles fibers were faster to fire communication signals back to the brain than resistance trainers.

"The communication between the brains and their muscles was slightly different than the resistance trainers and sedentary individuals," said the study’s lead author Trent Herda, a professor of health, sport, and exercise sciences, in a press release. "This information also suggested that resistance trainers and those who are sedentary were more likely to fatigue sooner, among other things."

Herda went on to explain that these results provide new clues into which exercise the human body is naturally designed to handle. However, the results need to be replicated on a larger scale with participants from a wide variety of athletic backgrounds before researchers can determine the type of training that fosters a speedier connection between muscle fibers and the brain — running or all aerobic exercise.

This isn’t to say that runners who strength train are hindering this connection. In fact, it might be just the opposite: Previous research has shown elite runners who combine lower body strength training with their regular routine improve their maximum running speed by 23.1 percent. And weight trainers who practice speed work for eight weeks can improve both their speed and ability to lift more weight than those who solely rely on weight training.

Muscles use oxygen to work, and by increasing lean muscle mass, the body’s ability to use oxygen and burn calories inevitably increases. Based on the growing body of research on how muscles handle exercise, incorporating a balance of running and weight training may yield the greatest benefits for the human body.

Source: Herda T and Trevino M. The effects of chronic exercise training status on motor unit activation and deactivation control strategies. Journal of Sports Sciences and Muscle and Nerve. 2015.