ASSESSMENT OF EXTENSOR AND FLEXOR STRENGTH IN THE INDIVIDUAL GONARTHROTIC PATIENT - INTERPRETATION OF PERFORMANCE CHANGES

The intra-session and inter-session reproducibility of knee extensor a nd flexor strength measurements were examined in 21 gonarthrotic subje cts (ten women and eleven men). Using the Cybex 6000 dynamometer, isok inetic peak torque and total work at 30 and 120 degrees/second and iso metric peak torque were measured three times on separate days within t wo weeks by the same examiner. The reproducibility of walking and stai r climbing time measurements was also assessed. The concept of critica l difference (i.e. the difference between two measurements which would be statistically significant when applied to a reference group in ste ady state) for the interpretation of muscle strength data obtained by monitoring individual patients is presented. Individual coefficients o f variation (CV) were calculated for each muscle strength variable. De pending on the velocity and on whether peak torque or total work were measured, the median CV of intra-session and inter-session extensor st rength measurements ranged from 1.5-4.9% and 7.4-10.1%, respectively. CVs for flexor strength measurements were significantly higher. Substa ntial variability of within subject variances were found, e.g. the 80% central range of CVs for extensor torque at 30 degrees/second was 2.5 -29.5% (inter-session). Calculated from CVs, critical differences for inter-session measurements exceeded 30% for all muscle strength variab les. Median CVs for walking and stair-climbing time were 7.0% and 4.9% , respectively. In conclusion, the large CVs and corresponding critica l differences may be a major limitation in the use of muscle strength measurements in the individual gonarthrotic patient.