Quantitative characterization of torpor-associated behaviors in mice.

Torpor is a hypometabolic and hypothermic state that enables small mammals such as mice to conserve energy under harsh conditions. While its physiological features have been extensively studied, behavioral signatures remain poorly characterized, partly due to limited quantitative tools. Here, we developed a posture-based framework to quantify torpor-associated behavior and test whether posture features help distinguish fasting-induced torpor from physiologically similar states. During torpor, mice actively suppress locomotion and adopt a curled-up posture with increased body width, head angle, and shortened body length as body temperature (Tb) falls. In contrast, adenosine monophosphate (AMP)-induced torpor-like state produces a stretched posture despite similarly reduced Tb, enabling robust discrimination. Using unsupervised analyses of aligned body-part coordinates, we further demonstrated that torpor-associated postural features differ from those during curled-up bouts in sleep and during cold exposure. These findings establish posture as a quantifiable behavioral marker that complements Tb and metabolic rate criteria and provide a noninvasive computational approach to refine torpor detection.