Electromyographic and Cardiorespiratory Responses of Load Carriage at Different High Altitudes with Varying Gradients

Manual load carriage is performed by Indian Army soldiers at different high altitudes (HA) in day to day operation. Such task puts extra stress on cardiorespiratory and skeletomuscular systems. A study was designed to find out the effect of electromyographic and cardiorespiratory responses of load carriage at different high altitudes with varying gradients. Eight healthy Indian infantrymen (mean (± SD) age of 27.2 (± 3.9) years, height of 171.1 (± 2.5) cm, and weight of 66.8 (± 6.7) kg) participated in the study. They were acclimatized at two heights (3550 and 4300 m). On completion of their acclimatization each participant was checked for healthy cardiorespiratory signs and subsequently they walked on a motorized treadmill at a speed of 3.5 km.hr^-1 and 0% and 10% gradients under three different experimental load carrying conditions (0, 10.7 and 21.4 kg). Continuous electromyography of three pairs of leg muscles i.e. vastus medialis, gastrocnemius, and tebialis anterior and breath-by-breath recording of oxygen consumption (VO₂) and heart rate (HR) were recorded during the experiments. Relative work load (RWL) was calculated from maximum aerobic capacity at respective high altitudes. High altitude had significant effects on the responses of gastrocnemius and vastus medialis muscles as well as on VO₂ and RWL. Increased responses of VO₂ and leg muscle could be attributed to withstanding the stress of HA and strain of load carriage at steep slopes.