STUDY OF FORCE AND CROSS-SECTIONAL AREA OF ADDUCTOR POLLICIS MUSCLE IN FEMALE HIP FRACTURE PATIENTS

OBJECTIVES: To determine the extent of muscle weakness in older female hip fracture patients compared with healthy older and young women; to determine the extent to which this weakness is caused by a decline of the force produced per unit area of muscle rather than by a decline i n muscle bulk; and to investigate the mechanism of the decline in forc e per unit area. DESIGN: This was an open study of three groups of sub jects, two age matched older groups and one young group. SETTING: Univ ersity College London, Royal Free Hospital, and St. Thomas's Hospital, London. PARTICIPANTS: Twenty-nine older female hip fracture patients (mean age 85.6 +/- 0.9 SEM), 18 healthy older women (mean age 84.7 +/- 1.2 SEM), and 43 young women (mean age 28.9 +/- 1.2 SEM). MEASUREMENT S: Adductor pollicis muscle maximum voluntary force (MVF) during isome tric and pliometric contractions and cross-sectional area (CSA), body weight, height, and demi-span. RESULTS: Isometric MVF was lowest in th e hip fracture group. In both older groups, isometric MVF and CSA were lower than in the young women. Only part of this weakness in the olde r groups could be explained by the smaller CSAs. The isometric force p er unit area (MVF/CSA) was also lower in both older groups, the hip fr acture patients again having the lowest values. Analysis of variance s howed a significant difference between groups. The age-related decline s in pliometric force were much less than the declines in isometric fo rce. This resulted in an increase in the pliometric/isometric force ra tio both for the hip fracture patients and for the healthy older women compared with that for young women. CONCLUSION: In comparison with th e results from young women, the adductor pollicis muscles of female hi p fracture patients were even weaker than those of healthy older women when normalized for muscle size. This decline in isometric MVF/CSA ac counted for at least half of the overall weakness in the hip fracture patients. Inasmuch as pliometric force is maintained in situations whe re weakness is caused by a decline in the force produced per muscle cr oss-bridge, this is the likely mechanism of the declines in isometric MVF/CSA observed in this study.