Gender differences in sensorimotor characteristics associated with the performance of a manual dexterity task at shoulder height.

Women report more neck/shoulder musculoskeletal disorders in association to low-force, dexterous work. However, it is unclear if this may be due to gender differences in sensorimotor patterns while performing such tasks. Twenty-nine asymptomatic adult volunteers (15 men, 14 women) performed a neck/shoulder fatiguing task involving screwing and unscrewing bolts placed at shoulder height until scoring 8 on a Borg CR-10 scale. During the task, performance (bolts/min) was measured, and electromyography (EMG) was recorded at eight neck/shoulder muscle sites to compute Root Mean Square (RMS), Motor Variability and Normalized Mutual Information (NMI). Before and after the task, Purdue pegboard and shoulder joint position sense were measured. Even though muscle fatigue was evidenced by neck/shoulder EMG results, shoulder proprioception was not affected by the fatiguing task while screwing and Purdue pegboard performance actually improved (p < 0.001). Women displayed overall higher RMS and NMI values (e.g. 80% higher UT RMS, 42% higher AD RMS). Thus, although task performance and proprioception did not deteriorate and were not different between genders, gender differences in EMG measures may help understand the sex-specific muscle fatigue mechanisms associated to shoulder height dexterous work, and may help explain the higher rates of neck/shoulder injuries in women.