Forearm muscle hemodynamic responses in healthy men during a seven-hour exposure to repetitive ulnar deviation task – A psychophysiological study

Abstract The purpose was to evaluate vascular hemodynamics in the forearm of fourteen healthy men over a seven-hour workday of repetitive work at and above their acceptable workload. Participants performed an ulnar deviation task at a frequency of 15 repetitions per minute for seven hours: at their psychophysically chosen acceptable torque (day 1), and at 25% above the acceptable torque (day 2). Hemodynamic responses (Tissue oxygenation index [TOI] and Tissue Hemoglobin Index [THI]) from the carpi ulnaris flexor and extensor muscle regions of the right hand were collected for the last 5 min of every hour of task performance. Participants selected their acceptable torque as 3.97 ± 2.5 N.m. (minimum: 1.0 and maximum: 9.8 N.m.). During task performance from 1 to 7 h, both tissue hemodynamic responses were not influenced by increasing the workload to above their acceptable level ( P  > 0.05). Therefore, increasing the acceptable load by 25% will not diminish the adequate supply and delivery of oxygen to the muscle regions recruited. When blood flow to the forearm was occluded (for 1 min) immediately after the final repetition of the seven-hour task, the half-time recovery, a noninvasive indicator of muscle oxidative capacity, was not significantly different between workloads (average TOI: 10.2 s at the acceptable workload versus 10.8 s at 25% above the acceptable workload, P  > 0.05; and average THI: 10.1 s at the acceptable workload versus 10.0 s at 25% above the acceptable workload, P  > 0.05). This is a remarkable finding as we hypothesized that recovery in each muscle might be longer for a workload that is greater than the acceptable level for an individual. The fact that hemodynamic responses were also similar during recovery from the task performance across both workloads imply the protectiveness of the psychophysical approach in assessing the physical ability of workers without anoxia or tissue hypoxia, thereby posing no injury to the muscles recruited. Relevance to industry Scientific discipline of “Psychophysics” has been instrumental in developing safe levels of workload to workers exposed to variety of occupational activities without risking injury or adverse health effects. The present optical spectroscopy-related study is an excellent example of integrating two scientific disciplines: Psychophysics and Work physiology in examining the influence of a seven-hour repetitive work exposure on muscle hemodynamics of the upper extremity.