Knee extensor and flexor strength in elderly women after hip fracture: Assessment by the Cybex 6000 dynamometer of intra-rater inter-test reliability

Abstract

The reliability of knee extensor and flexor strength measurements was assessed in 20 women (age 68-88 years) who had experienced a hip fracture two to four weeks before but who were otherwise healthy. Using the Cybex 6000 isokinetic dynamometer, isokinetic knee extensor and flexor strength (peak torque, total work and power) at 30 and 120°/second and isometric knee extensor and flexor strength (peak torque) were measured by the same examiner in both legs, successively, on four separate days within one week. Compared with the non-involved leg, the median reduction in peak extensor and flexor torque of the involved leg was 50% (p < 0.001). With the protocol used, no significant change in muscle strength occurred during the test period. Individual coefficients of variation (CVs) were calculated for each muscle strength variable. Depending on whether torque, work or power were measured, the median CVs of extensor and flexor strength measurements of the non-involved leg ranged from 5.6-14.6% and 10.8-28.6%, respectively. The corresponding CVs for the involved leg were 10.9-22.1% and 13.0-35.2%. Substantial variability between individual CVs were found for all strength variables. In conclusion, although muscle strength measurements may be applicable when comparing larger groups of hip fracture patients, the large CVs may be a limitation in monitoring individual patients. This finding should be taken into consideration when planning individual training programmes.