Knee Joint Position Sense Following Exercise in Various Environments

Impaired joint position sense due to fatigue during physical activity can increase risk of musculoskeletal injury. The impact of thermal strain during exercise in extreme environments on joint position sense is relevant to military personnel and has not yet been determined. Therefore, the purpose of this study was to test the hypothesis that active knee joint position sense would be impaired following loaded walking, and that the impairment would be greatest in a hot environment. In a crossover design, 23 females completed a 68-minute treadmill walking protocol (0.48-1.70 m/sec) while wearing a military rucksack loaded to 33% of body mass in four dry environments (20% relative humidity) of varying air temperatures: 10°C (Cool), 22°C (Temperate), 31°C (Warm), 40°C (Hot). Before and after walking, an active knee joint repositioning test with a target angle of 30° of flexion was completed in a prone position using an electrogoniometer to measure the joint angle. Gastrointestinal temperature was measured using an ingestible telemetry pill. Linear mixed model ANOVA compared differences among environments and time, α=0.05. Data are presented as mean ± standard deviation. The knee flexion repositioned angle was greater after walking compared to before walking (p<0.01) (Cool: Pre: 34.5±5.7°, Post: 35.9±5.9°; Temperate: Pre: 34.3±4.4°, Post: 37.0±5.4°; Warm: Pre: 34.4±4.2°, Post: 35.5±7.4°; Hot: Pre: 34.2±5.4°, Post: 37.1±7.3°), leading to a greater repositioning error after walking compared to before walking (p<0.01) (Cool: Pre: 4.5±5.7°, Post: 5.9±5.9°; Temperate: Pre: 4.3±4.4°, Post: 7.1±5.4°; Warm: Pre: 4.4±4.2°, Post: 5.5±7.4°; Hot: Pre: 4.2±5.4°, Post: 7.1±7.3°). End of walking gastrointestinal temperature was lower in Cool (37.47±0.36°C) compared to all other trials (Temperate: 37.73±0.31°C, p<0.01; Warm: 37.71±0.27°C, p=0.02, Hot: 37.78±0.18°C, p<0.01), with no differences among the other environments (all p>0.05). In line with our hypothesis, participants had a 2° increase in knee flexion repositioning error during a joint repositioning test following one hour of walking, however, environment did not influence this response likely due to only mild elevations in gastrointestinal temperature and no differences among temperate and heated trials. Research is needed to determine if these patterns in joint position sense remain following exercise in more thermally stressful environments and longer bouts of exercise, and whether an increase of 2° of knee flexion repositioning error predisposes individuals to an increased risk of musculoskeletal injury. The views expressed are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, United States Government, or CoachMePlus. Funding for this project was provided through the Medical Technology Enterprise Consortium (W81XWH-22-9-0014). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.