Effects of age, gender, and task parameters on fatigue development during intermittent isokinetic torso extensions

This study investigated the effects of age, gender, and task parameters on muscle fatigue during prolonged isokinetic torso exercises, and assessed the sensitivity of EMG-based measures to fatigue. Two groups of 24 participants (older: 55–65 years, younger: 18–25 years), with gender balanced within each group, performed repetitive intermittent torso extensions until exhaustion. Effort levels were set to 30% and 40% of individual maximum voluntary contraction (MVC) and work–rest cycles had durations of 30 and 60 s with a 50% duty cycle. Electromyographic (EMG) signals were obtained bilaterally from the paraspinal muscles. EMG-based fatigue measures, along with declines in MVC and changes in ratings of perceived discomfort, were used to evaluate fatigue progression. While the older group had 23% less initial strength than the younger counterpart, effects of age and gender on fatigue were marginal. However, significant interactive effects of age and gender with effort level were found. These findings overall suggest the importance of carefully considering individual factors and task parameters in designing jobs requiring repetitive torso efforts. In the dynamic torso efforts investigated, the sensitivity of EMG measures to fatigue was relatively low.Relevance to industryManual material handling tasks such as lifting are often characterized by intermittent dynamic torso efforts. This paper provides evidence regarding age-related differences in torso capacity (strength, fatigue, and endurance), and the influences of effort level and cycle duration. These results can be used for task evaluation and design, and to address older workers in particular.