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performed 25 to 82 percent better than subjects with carpal tunnel syndrome. Age contributed 6 percent of the total variance for pinch rate and 7 percent of the total variance for the time below the lower force level. The results suggest that patients with carpal tunnel syndrome may experience similar functional psychomotor deficits in daily living and manual work activities. Schiefer et al. (1984) demonstrated that finger skin temperature and performance on manual dexterity tests decreased as the ambient air temperature decreases.

Upper Limb Summary

Overall, the literature reveals that there are strong relationships between physical loads in the workplace and biomechanical loading, internal tolerances, and pain, impairment, and disability. Although many of these relationships are complex for the upper limb, the associations are clear. The biomechanical literature has identified relationships between physical work attributes and external loads for force, posture, vibration, and temperature. Research has also demonstrated relationships between external loading and biomechanical loading (i.e., internal loads or physiologic responses). Relationships between external loading and internal tolerances (i.e., mechanical strain or fatigue) have also been demonstrated. Finally, relationships have been shown between external loading and pain, discomfort, impairment, or disability. Although the relationships exist, the picture is far from complete.

Individual studies have for the most part not fully considered the characteristic properties of physical work and external loading (i.e., magnitude, repetition, or duration). Few studies have considered multiple physical stress factors or their interactions. The absence of these relationships, however, does not detract from the basic theoretical construct of the load-tolerance model. In fact, it suggests the need for additional research.

When considered together, a broader picture emerges. The existence of relationships together supports the load-tolerance model presented in this report. Furthermore, biomechanics forms the basis to reduce external loading. The relationships that are established indicate appropriate interventions for reducing exposure to external loads in the work environment through ergonomics and work design. Future research efforts targeting the missing relationships may help provide additional workplace interventions for preventing and reducing the risk of work-related disorders.

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