Shoulder muscle tenderness and physical features of female industrial workers

Physique, muscle strength, and jump-step scores of female industrial workers, ages 17--34, were studied in relation to tenderness of shoulder muscles for five groups, (A) character display operators, (B) fluorescent lamp assemblers, (C) photographic film rolling workers, (D) teachers and nurses of handicapped children, and (E) office workers. No significant differences were found between the five groups in mean body height, body weight, and skinfold thickness, but mean knee extension force of groups A and C and mean back muscle strength of groups A, B, and C was significantly lower than that of group E. Workers of groups C and D with a low tenderness threshold of m. trapezius of 0.6 kg/cm2 or less had stiff shoulders more frequently and lower force levels of knee extension, back muscle, and upper arm abduction than those without tenderness. No similar tendency was found for groups B and E. Further, among workers with objective signs of occupational cervicobrachial disorder, there were few whose knee extension force or jump-step scores were above the averages of normal office workers. Shoulder muscles of such operators were revealed to be continuously contracted during operations. The possible effects of chronic fatigue due to repetitive operations on developing localized tenderness and occupational hazards are discussed.