A growing number of workers in modern automotive assembly plants are confronted with occupational tasks involving repeated high-impact hand strikes. Such repetitive physical workloads account for diseases of soft tissues or musculoskeletal disorders in the hand, wrist, or entire upper body. The purpose of this review was to identify and discuss the most pertinent occupational and physiological investigations concerning such hand strikes with particular emphasis on the biomechanical parameters examined. Articles were drawn from four databases to identify publications about occupational hand strikes. First, studies were selected that evaluated hand impact loads measured with the help of force measurement devices.For a deeper understanding of biomechanical factors regarding hand impacts, the scope of the search was extended to include ancillary studies about impacts on wrists or elbows. Overall, 945 abstracts were screened, and five full-text articles were included in the final review. In addition, 34 ancillary articles about impact stress on the hand-arm complex were discussed because of positive relations between high forces, repetition rates or acceleration, and progressing stress in the hand-arm complex identified in studies about critical biomechanical load limits, in the field of fall arrests and sports, i.e. tennis. Furthermore, studies about effective arm movements and body postures during hand strikes as used in martial arts were reviewed. Although certain biomechanical parameters are both known and well documented, studies available at present cannot sufficiently account for specific disorders in the wrist or arm that are triggered by occupational hand strikes.
The increase in repetitive strain injuries to the hand underscores the need for assessing and preventing musculoskeletal overuse associated with hand-intensive tasks. This study investigates the risk of overload injuries in soft tissue structures of the hand by analyzing the pressure distribution and location of peak pressure in the hand during snap-fit connection assembly in the automotive industry. The influence of the surface geometry of automotive trim components the pressure distribution and force imparted during strikes with the palm and the fist are investigated in a cohort of 30 subjects with extensive experience installing trim parts with snap-fit connections. Using the palm or fist (ulnar hand side) of the dominant hand, the subjects struck a simulation device with a flat, rounded, or edged surface geometry. The average peak force applied was 600 N (±122 N), nearly 3 times the force required to overcome the technical resistance of the snap-fit connector (220 N). Fist strikes exerted a 40% higher mean peak pressure and 18% higher mean pressure than did palm strikes. The pressure distribution in the region of the thenar eminence and soft tissue of the ulnar side of the hand did not differ between fist strikes on flat and edged surfaces. Considering the delicate anatomy of the hand, especially the hypothenar muscles on the ulnar side, assembling connection claps using the fist instead of the palm may prevent repetitive blunt trauma to the sensitive blood vessels and nerves in the palm.
This study determines the effects of increasing forces on different musculoskeletal load parameters, such as muscle activity and joint movement, during assembly taskrelated dynamic hand strikes and isometric push forces. Fifteen subjects (12 men and 3 women) were instructed to strike and push on a force plate in two selected conditions. In the first condition, the palmar surface of the dominant hand is oriented horizontal to the measuring surface; in the second condition, the body position is maintained, but the hand is turned 90°to allow the use of the ulnar side of the hand (fist strike position). The subjects accomplished four force levels in ascending order (i.e., 150, 250, 350, and 400 N) within the corresponding striking and pushing conditions. The extracted kinematic variables of interest were strike velocity, recoil velocity, force plate contact time, peak vertical reaction force component (force plate), force impulse, muscle activity, and maximum joint ranges of motion during the push or strike process. Differences in the results between pushes and strikes and, under certain circumstances, between fist and palm strikes were identified. Increasing push forces correlate with the muscle activity in the pectoralis and lower arm extensor muscles. The fact that, at push forces > 250 N, the subjects modify and adapt their upper body and arm posture to achieve the required force could reveal an obvious feasibility limit and explain why assembly workers tend to use their hands as a hammer.assembly, fist, hand strike, palm, push force | INTRODUCTIONAssembly tasks in different industries require effective performances of the working population. Manual activities, such as strikes or near static push forces with the hand, have gained steady attention in the broader literature. These working methods are time efficient and do not require tools, such as screws and glue. Especially, striking with the hand is an intuitive method of force transmission. Studies on the percussive behavior of humans during the Stone Age and even among prehistoric primates have revealed that hammering using
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