Postural Differences in Skin Temperature and Heat Flow from the Hand: Comparison of Standing, Supine, and Head-Down Tilt Positions

This study aimed to investigate posture-related variations in skin temperature and hand heat dissipation under simulated microgravity conditions.Eight young males (24 3 y) participated in three posture conditions: standing, supine, and 10 head-down tilt (HDT), which mimics a microgravity environment.Experiments were conducted in a climate chamber (24 1C, 60 5%RH).A water-perfused glove (7C circulating water) was used for the last 30 min during each 60-min trial to quantify hand heat extraction.Mean skin temperature showed no significant difference among the three posture conditions (32.8-32.9C),but the decrease from resting to posture phases was greater in the supine than standing condition (p < 0.01).Trunk temperatures increased significantly during both supine and HDT conditions, whereas finger temperature dropped sharply after glove cooling, with a larger decline in the supine and HDT posture conditions (p < 0.05).Heart rate and blood pressure were significantly higher in the standing posture than in the two recumbent conditions (p < 0.05).Despite physiological redistribution of skin blood flow, hand heat extraction did not differ significantly among the postures (1.56 1.00, 1.48 0.88, and 1.69 0.92 kcalmin -1 , respectively).Thermal sensation, comfort, and dizziness scores showed no significant variation across the three conditions.These findings suggest that posture-induced changes in blood redistribution alter local skin temperature but have limited impact on overall hand cooling efficiency.The results provide fundamental insights into human thermoregulation under simulated microgravity, supporting the design of liquid-coolded garments for future manned space missions.