Purpose: The purpose of this experiment was to evaluate the effect of load carriage in a range of temperatures to establish the interaction between cold exposure, the magnitude of change from unloaded to loaded walking and gradient. Methods: Eleven participants (19-27 years) provided written informed consent before performing six randomly ordered walking trials in six temperatures (20, 10, 5, 0, -5, and -10 °C). Trials involved two unloaded walking bouts before and after loaded walking (18.2 kg) at 4 km/h, on 0 and 10% gradients in 4 min bouts. Results: The change in absolute oxygen consumption (VO2) from the first unloaded bout to loaded walking was similar across all six temperatures. When repeating the second unloaded bout, VO2 at both -5 and -10 °C was greater compared to the first. At -10 °C, VO2 was increased from 1.60 ± 0.30 to 1.89 ± 0.51 L/min. Regardless of temperature, gradient had a greater effect on VO2 and heart rate (HR) than backpack load. HR was unaffected by temperature. Stride length (SL) decreased with decreasing temperature, but trunk forward lean was greater during cold exposure. Conclusion: Decreased ambient temperature did not influence the magnitude of change in VO2 from unloaded to loaded walking. However, in cold temperatures, VO2 was significantly higher than in warm conditions. The increased VO2 in colder temperatures at the same exercise intensity is predicted to ultimately lead to earlier onset of fatigue and cessation of exercise. These results highlight the need to consider both appropriate clothing and fitness during cold exposure.
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