Insertion loads and forearm muscle activity during flexible hose insertion tasks

OBJECTIVE: To quantify the physical demands of hose insertion tasks in automotive assembly operations and how they are affected by method and the mechanical interference between the hose and the flange. BACKGROUND: Insertion tasks were identified by workers as physically demanding and can often lead to fatigue or losses in production attributable to pain or injury. METHODS: Six male and 6 female participants pushed a 25.4-mm flexible rubber hose onto a stationary flange during simulated insertions. Three insertion methods -- rock, straight, and twist -- were examined in the study. Muscle activity of the finger flexors was recorded to estimate grip effort during the simulated insertions. RESULTS: The twist method (114.8 N) resulted in a 26% reduction in axial force compared with the straight method (155.7 N). Average muscle activity ranged from a low of 14% maximum voluntary contraction (MVC; men, straight method) to a high of 67% MVC (women, twist method). Hose resultant forces ranged from a low of 52.2 N to a high of 461.1 N for all participants. Men exerted 6% higher resultant forces with 37% less muscle activity than women. CONCLUSION: There are situations when the 26% reduction in the axial force attributable to twisting may be helpful during an insertion, despite the fact that forearm muscle activity was highest for both male and female participants during twisting insertions. APPLICATION: The results of this study can be applied to the future design of tasks that involve the joining of two parts such as a hose and flange.