The perception of exertion during load carriage

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Abstract
The perception of exertion is a complex phenomenon in which local muscular and joint factors, as well as central cardio-respiratory factors are thought to play important roles. This study examined the effects of backpack load carriage on ratings of perceived exertion (RPE). Ten well conditioned young men carried 0,20 and 40% of body mass in an external frame backpack at two speeds normalized for stature (0·75 and 0·95 statures per second). Steady-state ventilation, cardiorespiratory and RPE data were collected during the last 5 minutes of each of six randomly administered 10-minute walks on a motorised treadmill. With the exception of breathing frequency (which did not change), ventilatory, cardiorespiratory and RPE responses increased linearly with increases in load carried and relative speed. Correlations calculated between RPE and cardio-respiratory measures indicated a reasonably high degree of relationship ([Vdot]O2, r = 0·75; HR, r = 0·47; [Vdot]I, r = 0·58). However, when the increment in RPE over its maximum range was compared to the relative change in heart rate and oxygen consumption, it was observed that as soon as added load was carried the perception of exertion increased almost twice as much as did the cardio-respiratory measures when compared with the non-loaded walks. This may lend support to the contention that ‘local’ factors, if accentuated by load carriage, can dominate the overall perception of exertion.