The effect of loaded work on cardiopulmonary function, maximum acceptable work duration, and repeated sprint ability

Load carriage is a requirement of certain occupations such as the military and fire and rescue services. The nature of work within these occupations may be exhaustive, submaximal, and repetitive. It is therefore necessary to quantify the physiological demand of load carriage during both exhaustive and submaximal work, and to provide workplace recommendations on task duration for work involving load carriage. Considering that restricting the chest wall affects pulmonary mechanics, load carriage may influence the contractile performance of the diaphragm. Since repetitive, high intensity work is also common in these occupations, it would be useful to determine if load carriage influences the performance of subsequent high intensity work. As a result, three laboratory experiments were conducted. Firstly, exhaustive treadmill exercise was performed under three experimental conditions: control (unloaded), load (22 kg weighted vest), and restricted (chest strapped). Second, submaximal treadmill exercise with a 22 kg external load was performed under five exercise conditions: 30, 50, 60, 70, and 80% of peak oxygen uptake. Finally, repeated sprints were performed on a cycle ergometer immediately following each of the five submaximal exercise conditions. During exhaustive exercise combined with load carriage, exercise tolerance was significantly reduced (P<0.05), and the degree of this reduction was a function of body mass. Furthermore, loading or restricting the chest caused significant reductions in maximum voluntary ventilation, inspiratory time, and expiratory time (P<0.05). However, diaphragmatic contraction velocity and excursion were not influenced by exhaustive exercise with external load or restriction. During submaximal exercise with load, peak heart rate was the most appropriate measure of acceptable work duration. Therefore, load carriage at 30% of peak oxygen uptake may continue for up to 3.5 hours, whereas work at 80% of peak oxygen uptake should not exceed 6 minutes. Finally, prior activity beyond 60% of peak oxygen uptake affects the performance of subsequent high intensity work. Therefore, where repetitive sprint ability is required, prior activity should not exceed 60% of peak oxygen uptake.