Muscular Responses To Different Magnitude Of Load Carriage And Uphill- Downhill Grade Combinations And Its Effect On Cortisol Concentration In Indian Soldiers

Abstract

ntroduction The fundamental necessity for human walking is the appropriate activation of leg muscles in response to changing conditions. For example, walking uphill and downhill is a common part of many of our daily activities. Walking involves a variety of biomechanical processes, and electromyographic recordings offer some insight into how the neuromuscular system adapts to such actions. It is generally acknowledged that cortisol is the physiological marker of stress, and testing salivary cortisol levels is a common procedure to identify the impact of stress brought on by vigorous physical exercise on an individual. During deployment and training, Indian soldiers must carry loads and hike up and down steep mountain slopes in the Himalayas. This is an unavoidable aspect of military life. This study investigated how the muscle activities and cortisol responses were affected by various magnitudes of load along with incremental-decremental gradients while walking on a treadmill. Methodology Twelve healthy male Indian soldiers aged 24.8±2.9 yrs, height: 173.76±7.4cm and weighing 66.2±6.4kg were the participants included in the present study. In this experiment participants walked continuously for 1 hr in each uphill and downhill gradients for 6 mins. Total duration of walk was 6 mins x 10 gradients, i.e. 60 mins. All the participants walked at 3kmhr-1 speed carrying load of 0.0 kg, 10.7 kg and 21.4 kg. They walked initially uphill at 0%, 5%, 10%, 15% and 20% gradients before moving on to gradients of -20%, -15%, -10%, -5%, and 0% downhill. Every participant completed 3 continuous uphill and downhill (1 speed x 3 loads x 1 gradient protocol) load carriage experiments on 3 different days. During each experiment the activities of Erector spinae (ES) and Vastus medialis (VM), of both sides were monitored by surface Electromyography along with the pre-test and post-test concentration of salivary Cortisol. Result Significant effects of gradient on the knee extensors were observed. Load and gradient had a significant effect on ES muscles activity, along with Cortisol concentration. It was observed that while walking with 21.4kg loads at 3km.h-1 speed the activity of both the muscles and Cortisol concentration increased maximally compared to other conditions. The activity of the muscles viz. ES increased up to 252% during uphill walking. In case of VM muscles, downhill walking had more effect on the muscle’s activity than uphill walking [Right Vastus medialis (RVM): 290%, Left Vastus medialis (LVM): 280%]. When walking at a 3 kmhr-1 speed unloaded, the cortisol concentration was raised by 22%, and when walking at the same speed with a 21.4 kg burden, it climbed by 77%. As the influence of time was taken into account, the exercise-induced stress resulted in a considerable rise in cortisol concentration as compared to pre-exercise settings. Conclusion This form of strenuous activity especially on the knee extensors predisposes the risk of muscular injury and early onset of fatigue. An increase in cortisol levels was also observed, indicating the level of stress that had been induced. Hence, the combat fitness of the military personnel may be reduced. Military training schedule should therefore be designed accordingly to reduce the incidence of injuries.