The Physiological And Performance Effects Of Varying Load Center Of Mass Position During Load Carriage At 7.5 Km.h-1

Abstract

PURPOSE The aim of the study was to determine and compare the physiological and performance effects of varying center of mass positions during load carriage at a speed of 7.5km.h−1. METHODS Ten male volunteers (20.54 ± 0.92 yrs, 74.32 ± 7.60 kg) exercised on a level treadmill at 7.5 km.h−1 carrying a 25 kg load. Each participantr repeated the trial 3 times, for the 3 center of mass positions of high, mid or low. These positions were randomly assigned for each trial. The physiological variables measured included oxygen consumption (VO2), heart rate (HR), respiratory exchange ratio (R), rating of perceived exertion (RPE). Performance testing was conducted using the Standing Broad Jump and Zig-Zag Agility Run prior to the 45 minute load carriage exercise protocol and at the end of 15 minute rest interval post exercise. RESULTS VO2 was significantly lower in the high position (37.02 ± 7.41 ml.kg−1·min−1) compared to the mid and low positions (38.35 ± 6.03 ml.kg−1·min−1, 39.37 ± 4.65 ml.kg−1·min−1 respectively). HR, RPE and R did not change significantly between the high (176.69 ± 23.02 bpm, 15.67 ± 1.63, 1.13 ± 0.13 respectively) and low load positions (176.11 ± 24.61 bpm, 15.50 ± 1.52, 1.06 ± 0.06 respectively). Post rest jumps and run times were not significantly different from pre-exercise jump and run times. CONCLUSION The results of this study suggest that load placement is an important consideration affecting the physiological, subjective and performance responses to load carriage. At 7.5 km.h−1, it was found that packing heavier items at the top portion of the backpack might be the most energy efficient model of load carriage. Performance measures of standing broad jump and agility run times did not appear to be affected by the exercise bout with load carriage and indicate that the 15-minute compulsory rest may be sufficient to allow for full recovery.