Ten male subjects (71-8#xA0;kg, 22-2 years of age) with an average predicted maximal oxygen uptake of 50-0 #xB1; 2-2 ml/kg-min walked on the treadmill under two conditions: with an added load, and with an elevated gradient. In load carriage, velocity (1.34 m/s) and grade (10) were constant for all subjects with the added load ranging from an empty backpack to 50 of body weight in the pack. Heart rate and rating of perceived exertion (RPE) were determined for each workload. During unloaded walking at the same velocity, grade was varied while heart rate and RPE responses were monitored. Both variables increased linearly with increases in power output, but added load carriage brought about substantially larger increases in heart rate and RPE than did unloaded walking for equivalent increases in power. These differential responses are thought to be related to differences in muscular fatigue and biomechanical action.
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