One of the most rewarding parts of working out is the afterburn, as the body continues to use up calories at a higher rate hours after working out. Lucky for us, this well-deserved gift isn’t the only one of its kind. Researchers at UT Southwestern Medical center believe they’ve found another way that the body changes in the hours post-exercise. And the effects, they believe, last for as long as two days.
Kevin Williams, Ph.D., an assistant professor in UT Southwestern Medical Center’s internal medicine department and author of a new Molecular Metabolism paper, tells Inverse that high-intensity workouts don’t just change the cells of the body but also the neurons of the brain. Specifically, they change the behavior of neurons involved in the melanocortin system, which influences the body’s metabolism.
In his studies on mice, he saw how a single, intense workout could “reprogram” these neurons, causing the body to keep expending energy long after the workout was over.
“The melanocortin system, along with the leptin/leptin receptor pathway, are the two of the most potent anti-obesity and glucoregulatory systems in the brain,” Williams says. “Our results would suggest that a single bout of exercise may provide lasting changes in a brain circuit correlated with driving improved metabolism.”
Because the melanocortin system is highly conserved between humans and mice, Williams believes the post-workout effects he saw in the mouse brain might apply to those of humans as well.
The mice in the experiments adhered to a fairly brutal workout regimen, which consisted of variations on hour-long high-intensity workouts on treadmills (three 20 minute-intervals, for example). After the workouts, Williams examined changes in the behavior of the two types of neurons involved in the melanocortin brain circuit. Normally, these two neurons — the POMCs and the NPY/AgRP neurons — have two opposing different effects on appetite and energy burning.
When POMC neurons are activated, the body simultaneously craves less food but also burns more energy. Activated NPY/AgRP neurons, meanwhile, have the reverse effect: appetite increases, but the body burns energy less effectively. If you’re trying to get the most out of a workout, you want the POMCs to be active.
The mice that worked out, Williams found, had increased activity in the POMC neurons both right away and as long as two days later. In response, their NPY/AgRP neurons fired less frequently over that same time period. Just a single workout was enough to trigger this effect, he adds.
“In particular, the increased activity observed in POMC neurons persisted for two days after a single bout of exercise,” Williams explains, adding that this may be evidence of metabolic adaptation, or “reprogramming,” that happens in this brain circuit after exercising.
Exciting as the findings are, many questions remain. Williams is unsure why he’s seeing this pattens of neuron firing. Is it due to the intensity of the exercise? The duration? These are both questions he’s following up on in his future work.
One thing, however, appeared clear from his mouse studies. It seems like repeated training actually increased the POMC-activating effect of working out. As the mice got fitter, there appeared to be increasingly dramatic patterns of POMC activity in their brain tissue. With each bout of exercise, more POMC neurons fire, even if they’re still hyperactive because of a previous day’s workout.
“Possibly subsequent bouts of exercise provided an additive effect,” Williams says.
Even if training isn’t your goal, Williams’ work seems to indicate that taking a day off from working out every once in awhile won’t hurt. Even if you aren’t working out, somewhere deep in the brain, the right kinds of neurons may still be feeling the effects.
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