Work-related musculoskeletal disorders - exposure assessment and gender aspects

Sammanfattning: Work-related musculoskeletal disorders are widespread, and are, for unclear reasons, more common among females than in males. Several risk factors have been described; constrained and awkward postures, repetitive and/or force demanding motions, and lack of recovery. The exposure to such risk factors was systematically assessed in 116 male and 206 female fish-processing industry workers. Large differences were shown, females to a much higher extent performed repetitive work with constrained neck postures, while males had heavier, but more varied work tasks. Surface electromyography (EMG) was evaluated as a measurement method of muscular activity. An important aspect is time for recovery of muscle fibres, especially in work tasks that demand low level, long duration activity. Muscle fibres are recruited according to a predefined order, some them, probably, being active whenever the muscle is used. To assess recovery time in these, a method that quantifies resting time of the entire muscles is needed. Such a method, 'muscular rest', was further developed and validated. It discriminated well between workers in occupations with high and low prevalence of neck/shoulder myalgia. EMG is, moreover, extensively used to assess the level of muscular activity during work. Large differences have been shown between individuals that perform the same work task, which could be due to differences in strength or working technique, or to a measurement error. The precision of the method has been poorly known. Six females repeated three different work tasks at three different occasions. For m.trapezius, the variation between days (within individual) was small, 8%. For the forearm extensors, it was somewhat larger, 33%, probably because of less adequate normalisation. To study the impact of gender on the development of neck and upper limb disorders, 105 males and 172 females with identical repetitive and force demanding work tasks were examined. The prevalence of disorders was much higher among the females. Further, the physical exposure was quantified, separately for the genders, by EMG, as well as by inclinometry and goniometry for working postures and movements. When normalising to a maximal exertion, a significant difference was shown, with higher exposures for females. The relative peak load was 50% higher for m.trapezius, and 44% higher for the forearm extensors. Further, females had 45% less muscular rest in the forearm extensors, and 40% higher wrist flexion/extension velocity on the right side. It is likely that a substantial share of the excess morbidity among females can be explained by higher physical exposure at work.