Quantifying precision and speed effects on muscle loading and rest in an occupational hand transfer task

Musculoskeletal disorders of the upper limb are common among semi-automated occupational hand transfer tasks. Ten healthy adults were recruited (five males, five females). Surface electromyography (EMG) was collected from eight muscles of the right arm: Upper trapezius, supraspinatus, infraspinatus, brachioradialis, extensor carpi radialis, extensor carpi ulnaris, extensor digitorum indicis, and flexor digitorum superficialis. The task consisted of a repetitive transfer of a 1.8-kg part at 2, 3, and 5 s cycle times (CTs), using power and chuck grips, and under precision and non-precision conditions. EMG was quantified using the amplitude probability distribution function (muscle loading) and gaps analyses (muscle rest). For all muscles, static (tenth percentile APDF) loading exceeded 1% and the muscle rest from gaps was below 10% at 2 and 3 s CT. Precision increased loading in forearm muscles, and increased perceived difficulty (p<0.001). The findings suggest that precision increased the loading by about 43% in the distal musculature under the conditions tested.Relevance to industryThis study will be useful in modeling lower risk CT and designing precision jobs (e.g. hand transfer) in semi-automated industries. Muscle loading and rest as physiologic parameters are influenced differently by CT, grip type and precision requirements of a task.