The physiological demand of a loaded march at five incremental speeds

Purpose: The primary purpose of this study was to determine the physiological demand of a loaded march at five incremental speeds. The second purpose was to assess if the number of steps taken had an impact on the physiological demand. Methods: 31 participants from the RAF Regt undertook five walking speeds (3 km/h, 4.2 km/h; 5 km/h; 6 km/h and 7 km/h) for 5min. Participants performed the speeds in groups of four in an aircraft hangar on a flat concrete surface, each group was paced by the same tester. Participants wore standard fatigues, boots and Complete Equipment Fighting Order (31.5 kg). During the last minute at each speed steady state oxygen consumption (VO2) was measured using Douglas bag collections of 1min. The total number of steps taken by each participant during the final minute of exercise for each speed was counted. Heart rate (HR) was measured for the duration of the trial at 5 s intervals. Rating of Perceived Exertion (RPE) was recorded after each march, ten minutes rest was provided between each speed. Results: The relationship between body mass and absolute VO2 (L/min) was assessed at each speed, weak (R2 ranged from 0.095 at 3 km/h to 0.298 at 4 km/h; 5 km/h and 6 km/h reported lower R2 than 4 km/h) and moderate (R2 = 0.327 at 7 km/h) relationships were found. Mean (SD) VO2 (mL/kg/min) was 12.1 (2.6) mL/kg/min; 14.4 (2.1) mL/kg/min; 17.2 (2.6) mL/kg/min; 23.9 (2.9) mL/kg/min and 33.5 (3.5) mL/kg/min for each of the speeds in ascending order. A positive polynomial relationship was found between walking speed and relative VO2 (mL/kg/min) (y = 1.2395x2 -7.1769x + 22.071; R2 = 0.9617) and walking speed and HR (y = 4.4438x2 -31.758x + 16.6; R2 = 0.7954). Expressing the data as number of steps per km demonstrated a negative polynomial relationship with speed (y = 29.906x2 -436.6x + 2773.9; R2 = 0.8985) and VO2 (mL/kg/km) demonstrated a positive polynomial relationship with speed (y = 13.078x2 -119.1x + 473.63; R2 = 0.5387). Conclusions: The polynomial nature of the relationships exhibited suggests that walking at 3 km/h is less efficient than faster speeds. An independent contributing factor to this may be the relatively higher number of steps taken, thus the additional physical work of lifting a load more times over the same distance.