Prolonged self-paced hard physical exercise comparing trained and untrained men

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Abstract
Six fit male subjects (25 years, 180 cm, 72 kg, maximal [Vdot]O2 = 2 63 mmol kg-1 min-1 (590 ml kg-1 min-1)) and six sedentary male subjects (24 years, 175 cm, 73 kg, maximal [Vdot]O2=2 01 mmol kg-1 min-1 (45- 1ml kg-1min-1)) performed self-paced hard physical exercise while walking over a 17-07km course consisting of four different terrains (blacktop road, 4-02km; dirt road, 4-65 km; light brush, 4-35 km and heavy brush, 4-05 km). All subjects walked the entire course as fast as possible carrying no external load, 10 and 20 kg. Time on each terrain for individual subjects was used to determine walking velocity and predicted energy expenditure. Heart rate (HR) was recorded as each subject completed each terrain. Walking velocity and absolute predicted energy expenditure were not different between the two groups (p>0-05), and did not decline with time as the subjects traversed the course for any of the load carriage conditions. Relative energy expenditure, however, was significantly different (p2max and 44% [Vdot]O2max, respectively). Mean HR for the untrained group was also significantly greater (p<0-05) than that for the trained group over each of the four terrains. These data indicate that when men are required to do self-paced hard physical exercise of an extended duration (approximately 2-5-3-5 hours), their walking velocity and energy expenditure will remain constant. Fit individuals may be limited by an inability to walk fast enough to maintain the same relative energy expenditure as unfit individuals. Consequently fit individuals might be expected to further extend the amount of physical exercise performed without a fall in energy expenditure.