Gait alterations due to fatigue have been evaluated in strenuous jobs like firefighting but less is known about gait changes after less strenuous prolonged activity. PURPOSE: We tested the hypothesis that gait changes would be greater after manual labor tasks performed in the heat (30°C, 50% RH) vs temperate (20°C, 30% RH). METHODS: Fifteen healthy (BMI 23.6 ± 3.0) subjects (9 females) completed two experimental visits of simulated manual labor tasks in an environmental chamber set to either the hot (HT) or temperate (CON) condition. Tasks consisted of 6 rounds of a circuit of brick-laying for ten-minutes, shoveling rubber mulch for five-minutes, and five-minutes of rest for a total of two hours. Gait characteristics were evaluated before and after exertion by the subject walking at a self-selected pace over an instrumented walkway. Walking speed, stride length, right leg single support, swing time, stance time, gait cycle time, double support time and double support percentage were analyzed. Values are reported as mean ± SD. RESULTS: A time x condition interaction was seen for stride length (cm), double support time (sec) and double support percentage. No main effect or interactions were found for walking speed (steps/min) or right single support (sec). Swing time (pre: 0.41±0.03 vs post: 0.40±0.03 sec; p=0.03), stance time (pre: 0.73±0.08 vs post: 0.71±0.07 sec; p=0.02) and gait cycle time (pre: 1.14 ± 0.10 vs post: 1.11 ± 0.09 sec; p=0.01) decreased in the CO trial from pre to post. Heart rate increased between the seated baseline and the end of the sixth round in the HT condition (69±6 vs 137±2; p<0.001) and the CON condition (66±7 vs 127±24; p=0.02) and was greater in the HT condition. Core temperature (Tc) increased in the CON (37.3±0.2 vs 37.8±0.28°C; p<0.001) and HT (37.2±0.3 vs 37.8±0.4°C; p<0.001). No difference in Tc (p=0.53) was found between conditions. CONCLUSIONS: Minor changes in gait were identified after manual labor tasks in CON conditions which were not seen in the HT condition. Greater sympathetic arousal from work in the heat could be masking the changes seen after identical work in cool conditions.