Avid runners often report a euphoric “boost” during their workout that gives them the motivation to keep on running. Where the actual ‘runner’s high’ comes from though, may be surprising for those on the go. A study reports in Cell Metabolism that the emotional pick-me-up is modulated in part by the satiety hormone leptin.
In the study, mice with reduced leptin signaling in the brain ran twice as many miles on a running wheel compared to normal mice. The research suggests that declining leptin levels send a “hunger signal” to the brain’s pleasure center to generate the rewarding effects of running via the runner’s high. The study’s author, Stephanie Fulton explains, “based on these findings, we think that a fall in leptin levels increases motivation for physical activity as a means to enhance exploration and the pursuit of food. Our study also suggests that people with lower fat-adjusted leptin levels, such as high-performance marathon runners, could potentially be more susceptible to the rewarding effects of running and thus possibly more inclined to exercise.”
What is leptin you ask? It’s a fat cell-derived hormones that tells the brain when the body has enough fuel and energy. Low leptin levels have been associated with exercise addiction, fast marathon times, and training status in humans and greater running speed and duration in mice. To test the impact of leptin, Fulton and her team used genetically engineered mice that lacked a leptin-sensitive protein called STAT3, which monitors the leptin signal specifically in neurons that release the reward chemical dopamine. Normal mice ran 6 kilometers a day on a running wheel but the STAT3-deficient mice ran an impressive 11 kilometers per day. The STAT3-deficient mice also spent more time in the running-side of the chamber than the normal mice.
In addition to explaining a “runner’s high” the research has clinical implications for anorexia. Previous research showed that leptin signaling in the brain’s reward center inhibits wheel running in a rat model of anorexia-induced hyperactivity. Individuals with anorexia have low fat-adjusted leptin levels, associated with increased restlessness and hyperactivity.
Fulton and her team plan to test running rewards associated with food seeking behavior and also which neural pathways downstream of dopamine neurons contribute to the runner’s high. This could develop new ways to enhance stamina and increase the probability of success while foraging and hunting. While leptin is not the only metabolic signal controlling the rewarding effects of running, the research allows scientists to determine the precise role of dopamine, opioid, and endogenous cannabinoid signals to impact physical activity and its rewards.
In the meantime, physical fitness can provide tangible results to your health. From weight management to improved cardiovascular health, a little run can do a lot more than give you a “buzz.” If running isn’t for you though, and you’re worried about physical fitness, contact your doctor at the Medical Alliance of Southern New Jersey to discuss potential ways for you to feel and look your best.