The effects of heavy load carriage on physiological responses to graded exercise

Many emergency response occupations require heavy load carriage with backpacks. The purpose of this experiment was to study the effects of heavy load carriage on physiological responses and performance during graded exercise.

Fifty males (age: 28 ± 6 years, height: 182.8 ± 6.2 cm, mass: 85.4 ± 12.1 kg) provided written informed consent before completing two randomly ordered graded exercise tests to measure ventilatory threshold and peak oxygen consumption (˙VO2peak). During the loaded test, each subject carried a correctly sized and fitted 80 L backpack weighing 25 kg. Mass, volume and load distribution were consistent between all packs. Modified Balke treadmill tests were completed by walking at 1.5 m s(−1) with stage increases of 2% grade until exhaustion.

Analysis revealed a small but significant decrease in ˙VO2 at ventilatory threshold (3.9%) and peak exercise (2.5%) under load. Power output at ventilatory threshold and ˙VO2peak were significantly decreased by 23.6 and 11.1%, respectively, and test duration was reduced by 29.8% in the loaded condition.

While heavy load carriage had relatively small effects on physiological responses at ventilator threshold and peak exercise, the reductions in power output and test duration were more substantial. Despite the absolute mass of the pack and the large range of subject size, the only change in performance associated with body size was test duration. These results have implications for evaluation of fitness for duty in occupations where heavy load carriage is required.