2 Identification of the Maximum Acceptable Frequencies of Upper Extremity Motions in a Seated Posture

Empirical data is lacking that can be used to establish the acceptable levels of repetitiveness for various postures and forces for prevention of upper-extremity musculoskeletal disorders (UEMSDs). The present study examined the maximum acceptable frequencies (MAFs; motions/min.) of shoulder, elbow, wrist, and index finger motions at different force levels (1 and 4 kgf for shoulder, elbow, and wrist motions; 0.25 and 1 kgf for index finger motions) in a seated posture. Seventeen right-handed males in their 20s without having any history of UEMSDs determined their MAFs by using the self-adjustment method; work pulse (bpm) and rating of perceived exertion (RPE) were measured when working at MAF. The average MAFs of shoulder, elbow, wrist, and index finger motions were 24, 45, 56, and 128 at the high force level and 9, 20, 30, and 66 at the low force level, showing a significant interaction effect of joint motion and force on MAF. The average work pulses of wrist, elbow, and shoulder motions were about 1.5, 2.1, and 3.0 times that of index finger motion (4.2 bpm at the low force level and 5.7 bpm at the high force level). Lastly, the maximum average RPEs of shoulder, elbow, wrist, and index finger motions were observed at the shoulder, forearm, wrist, and finger regions with a range of 2.1 (weak) to 3.1 (moderate) in Borg’s CR-10 scale