Force variability and musculoskeletal pain in blue-collar workers

Blue-collar workers with physically demanding occupations have a high prevalence of musculoskeletal disorders accompanied by pain. Previous research has suggested that reduced motor variability may increase the risk of developing musculoskeletal disorders. Here we present preliminary data from an ongoing cross-sectional examination of physical performance in elderly manual workers. This paper includes data from 20 male workers (age 52–70 years). Handgrip force variability was measured using a digital hand dynamometer during an endurance trial where the workers exerted 30% of their maximal isometric contraction force until task failure. Absolute variability (standard deviation), relative variability (coefficient of variation), and the complexity of the force signal (sample entropy) were computed. The workers were dichotomized into two groups: no to mild pain/discomfort (No pain) and moderate to severe pain/discomfort (Pain) to investigate the effects of musculoskeletal pain on force variability. This dichotomy was done based on the rating of pain/discomfort within the last seven days, where workers reporting ≥3 score in the upper extremities were allocated to the pain group (Pain, n = 9, No pain, n = 11). No significant between-group differences in force variability during the endurance trial were found. Both absolute and relative variability increased significantly over time. These preliminary data do not support a difference in force variability between blue-collar workers with or without musculoskeletal pain or discomfort in the upper extremities.