Phillips S K, Woledge R C, Bruce S A, Young A, Levy D, Yeo A, Martin F C
Institute of Human Performance, University College London, Royal National Orthopedic Hospital, Stanmore, Middlesex, UK.
J Am Geriatr Soc. 1998 Aug;46(8):999-1002. doi: 10.1111/j.1532-5415.1998.tb02756.x.
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 in muscle bulk; and to investigate the mechanism of the decline in force per unit area.
This was an open study of three groups of subjects, two age matched older groups and one young group.
University College London, Royal Free Hospital, and St. Thomas's Hospital, London.
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).
Adductor pollicis muscle maximum voluntary force (MVF) during isometric and pliometric contractions and cross-sectional area (CSA), body weight, height, and demi-span.
Isometric MVF was lowest in the 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 older groups could be explained by the smaller CSAs. The isometric force per unit area (MVF/CSA) was also lower in both older groups, the hip fracture patients again having the lowest values. Analysis of variance showed a significant difference between groups. The age-related declines in pliometric force were much less than the declines in isometric force. This resulted in an increase in the pliometric/isometric force ratio both for the hip fracture patients and for the healthy older women compared with that for young women.
In comparison with the results from young women, the adductor pollicis muscles of female hip fracture patients were even weaker than those of healthy older women when normalized for muscle size. This decline in isometric MVF/CSA accounted for at least half of the overall weakness in the hip fracture patients. Inasmuch as pliometric force is maintained in situations where weakness is caused by a decline in the force produced per muscle cross-bridge, this is the likely mechanism of the declines in isometric MVF/CSA observed in this study.
