The impact of thoracic load carriage up to 45 kg on the cardiopulmonary response to exercise

The purposes of this experiment were to, first, document the effect of 45-kg thoracic loading on peak exercise responses and, second, the effects of systematic increases in thoracic load on physiological responses to submaximal treadmill walking at a standardized speed and grade.

On separate days, 19 males (age 27 ± 5 years, height 180.0 ± 7.4 cm, mass 86.9 ± 15.1 kg) completed randomly ordered graded exercise tests to exhaustion in loaded (45 kg) and unloaded conditions. On a third day, each subject completed four randomly ordered, 10-min bouts of treadmill walking at 1.34 m s⁻¹ and 4 % grade in the following conditions: unloaded, and with backpacks weighted to 15, 30, and 45 kg.

With 45-kg thoracic loading, absolute oxygen consumption (\( \dot{V}{\text{O}}_{2} \)), minute ventilation, power output, and test duration were significantly decreased at peak exercise. End-inspiratory lung volume and tidal volume were significantly reduced with no changes in end-expiratory lung volume, breathing frequency, and the respiratory exchange ratio. Peak end-tidal carbon dioxide and the ratio of alveolar ventilation to carbon dioxide production were similar between conditions. The reductions in peak physiological responses were greater than expected based on previous research with lighter loads. During submaximal treadmill exercise, \( \dot{V}{\text{O}}_{2} \) increased (P < 0.05) by 11.0 (unloaded to 15 kg), 14.5 (15–30 kg), and 18.0 % (30–45 kg) showing that the increase in exercise \( \dot{V}{\text{O}}_{2} \) was not proportional to load mass.

These results provide further insight into the specificity of physiological responses to different types of load carriage.