By Molly Daw

Faculty Mentor: Dr. Parrish Waters

Abstract

Physical exercise influences biological systems such as metabolism, cardiovascular health, and neural function. Its role in regulating circadian rhythm, the body’s internal “clock” that regulates wake-sleep cycles is less understood. This study examined how voluntary exercise affects circadian activity in mice. It was expected that limited access to running wheels would result in longer activity durations due to increased competition and higher energy availability from reduced overall exercise. Forty mice were split into two groups: one with limited wheel access (five cages with four mice and one wheel each) and another with unlimited access (five cages with four mice and two wheels each). Number of wheel revolutions were recorded daily over 26 days and statistical analyses were performed to determine differences in activity over the 12-hour light and dark phases. Mice with unlimited access showed greater activity during the dark phase, following typical nocturnal patterns. Those with limited access began running earlier, with significantly higher activity two hours before the dark cycle began. This shift likely reflects a behavioral adaptation to competition. These findings suggest that exercise availability can alter circadian activity timing. Limited access promotes earlier and extended activity, while greater access supports predominantly nocturnal activity in mice, emphasizing how environmental constraints shape circadian rhythms.