Physical variation in low-load work - physiological effects during exposure & recovery.

Trends in industry are leaning towards jobs that are more stereotyped at lower workloads. Physical variation is a potential ergonomic intervention. However, little is known of physiological response to different kinds of variation. To investigate this issue, three kinds of isometric contraction patterns with the same mean amplitude, cycle time, and duty cycle were compared. Fatigue responses were measured by multiple biomechanical and physiological approaches. In exercise, sustained and intermittent contractions with zero force had a greater number of statistically significant differences in fatigue responses. Intermittent contractions with amplitude ½ and 1½ of mean force had effects intermediate but close to the sustained contraction. In recovery, sustained contractions led to decreased twitch forces 24 hours post-exercise whereas both intermittent contractions recovered within 60 minutes. This suggests that time varying forces, even without complete muscular rest, may be a useful intervention to reduce local and perceived fatigue in workers performing low-load tasks.