A reference equation for normal standards for knee extensor isokinetic strength in Brazilian older women

Knee extensor strength assessment has been especially emphasized in older people, but lack of reference values limits its usefulness in geriatric evaluation.

The aim of this study was to develop a reference equation for knee extensor isokinetic strength standards in older women.

Knee extensor isokinetic tests at 60°/s were performed in 390 Brazilian older women aged 60-84 years (67.38 ± 5.56 years) and in a separate validation sample of 110 women (67.94 ± 6.13 years). A regression equation for peak torque (PT) was derived and compared to commonly used formulas: the equations of Neder and Gross. Age, weight and height were the only significant predictors (multiple R = 0.55; R² = 0.30; p < 0.001). The proposed equation was examined in the independent sample. Percent from predicted values was calculated and Bland-Altman plots were constructed.

Both the Neder and Gross equations significantly underestimated predicted PT values (both p < 0.001); mean bias were 6.79 and 6.75, respectively. The proposed equation [PT = 39.72 - (1.24 × age) + (0.44 × weight) + (69.70 × height)] was matched with the independent sample, with a percent predicted isokinetic strength of approximately 95%, a mean bias approximately 40% lower 4.23 than the other equations, and stable across all age groups.

Available equations for knee extensor isokinetic strength are not adequate for older women. The equation developed in the present study provided considerably lower average error and thus with more suitable reference values.