Effects of sustained manual work and partial sleep deprivation on muscular strength and endurance

Summary In a military field artillery trial, the effects of 8 days of sustained manual work and partial sleep loss on isometric right hand grip strength and upper and lower body anaerobic power (using the Wingate test) was investigated in 25 healthy young male soldiers. During the trial, the physical activity of each subject was essentially identical except that an experimental group (n=18) manually handled a large quantity of artillery shells (weighing 45 kg) and charges (13 kg), whilst a control group (n=7) merely simulated manual handling activities and did no lifting or loading of shells. The daily amount of sleep obtained by each group was similar (3 to 4 hours), as were their activity patterns and food and fluid intake. Isometric right hand grip strength for both groups fell progressively during the trial and did not return to pre-trial levels during 3 days of recovery. At the end of the 8 day trial, there were statistically significant reductions in the body weight (1.9%,p< 0.001), % body fat (7.1%,p< 0.001) and upper body mean power (7.3%,p<0.01) of the experimental group but not in the controls. Lower body peak and mean power were significantly increased at the end of the trial in both the experimental (14.7%,p<0.001 and 17.0%,p<0.001 respectively) and control (14.3%,p<0.01 and 15.0%,p<0.05 respectively) groups. Lower body power decrease was significantly increased (18.1%,p<0.05) in the experimental group but not in the controls. It is suggested that the increase in lower body anaerobic power may be associated with the increased level of physical activity during the trial ie a training effect, and that the decrease in upper body anaerobic power may be associated with the combination of unaccostomed arduous manual handling of heavy loads and partial sleep loss since it was only observed in the experimental group.