Brain Volume Predicts Skewed Locomotor Output and Lower Temporal Regularity

Daily locomotor activity patterns vary widely between individuals, reflecting underlying kinematic strategies, energetic trade-offs, and circadian regulation. Here we integrate wearable accelerometry and brain MRI to examine how locomotor kinematics (movement intensity and variability) relate to brain size through an allometric biomechanics lens, and how these links depend on time-of-day (temporal behavior scaling) and align with the pace-of-life continuum. In a cohort of adults (n = 52, 27 male), we found that individuals with larger brains exhibited slower, more intermittent daily movement profiles – characterized by lower overall activity, higher skewness and kurtosis of activity distributions, and reduced complexity (entropy) – suggestive of more controlled, energy-conserving behavior. In contrast, smaller-brained individuals had more continuous, regular, and symmetric activity patterns. Sex differences in circadian locomotor dynamics were also evident: females showed faster morning ramp-up and more symmetric activity distributions, whereas males exhibited greater daytime skewness and leptokurtosis, consistent with divergent circadian pacing. Regional correlations were sharpened when normalizing by overall brain size, localizing brain-behavior correlatoins to temporal (salience) and frontal cortices. Our findings reveal an allometric scaling of human activity rhythms: larger brain volume is associated with a “slower-paced” daily locomotor regimen, analogous to the slow-fast continuum observed across species. This diurnal structural coupling underscores how brain anatomy may influence not just how much we move, but how and when we move, supporting the idea that humans manifest individualized pace-of-life strategies rooted in neurobiology.