In a culture fixated on weight loss, diet, and exercise, we are all yearning for the next big finding that will give us more insight into becoming better athletes and living healthier lives. A recent study investigated a side of exercise that is often overlooked, but is nonetheless a growing health problem: exercise addiction.

This study provided evidence of actual physiological withdrawal from exercise deprivation in mice, as well as proved the relevance of a valuable research tool that can help scientists and engineers make monumental gains in exercise and fitness research.

In order to adequately model the withdrawal response from an avid exerciser, this study used selective lines of mice that were bred for high wheel running. Erik Kolb, Scott Kelly, and Theodore Garland from Dr. Garland’s laboratory at the University of California, Riverside report that these “high running” mice typically ran at higher speeds and ~ three times farther than control mice (Physiol Behav. 2013;112-113:49-55). What better way to study athletes than to use a mouse model of genetically superior athletes that have behaviorally driven athletic tendencies? The mice have the ability to run faster and want to run farther than your average house mouse. Thus, the high running mice used in this study are an invaluable mouse model for researchers studying athletes, exercise addiction, or any exercise related topic.

Kolb et al. set out to investigate the presence of cardiovascular withdrawal symptoms after the denial of exercise to the high running mice. In humans, as well as in mice, behavioral withdrawal symptoms such as anxiety and depression have been investigated in the context of exercise addiction. Garland’s group reports that in previous studies, the high running mice were found to have altered brain activity as well as behavioral tendencies indicative of anxiety and stress during periods of exercise deprivation. However, this is the first study that aimed to characterize an actual physiological withdrawal response from mice during periods without exercise.

To determine if there were cardiovascular discrepancies between an 8 day non-active, a 6 day exercise, and a 2 day exercise denial period, the cardiovascular state of each mouse was reported in terms of heart rate, systolic and diastolic blood pressure, and mean arterial pressure during each phase of the study. The key finding was that during periods of exercise deprivation, the high running mice exhibited lower systolic and diastolic blood pressure, as well as lower mean arterial pressure than during periods with exercise, all characteristic to withdrawal syndromes. Altered blood pressure is a known physiological indicator of physiological withdrawal and thus, this study provides the first evidence that exercise can actually be physically addictive and produce unwanted side affects upon cessation.

Investigation of the high running mice should continue to provide an array of new physiological findings regarding athleticism and exercise. As this study was the first to examine cardiovascular responses to exercise deprivation in the high running line of mice, and heart rate was used only as an inclusion criterion, an important next step might be an electrocardiographic study and comprehensive analysis of heart rate variability. Another interesting question regarding the high runner mouse is regarding postural and kinematic characteristics of their gait that may confer upon them their superior athleticism. Although these mice proved to be valuable research tools in the context of exercise withdrawal, their applications can clearly be extended to a wide range of topics including development, aging, and drug affects on athletes.