Fair as a percentage of normal using manual muscle testing of knee extensor strength.

We explored the extent to which fair knee extensors might be judged to be weaker than the normal knee extensors of healthy young adults. To obtain quantitative data for normal strength of knee extensors, we recorded knee torque in 20 healthy young subjects using an isokinetic dynamometer, and calculated muscle strength equivalent to fair, including the effect of inertial force, using a rigid body model. The results showed that fair torque as a percentage of actual normal torque at 60 degrees per second was 4.8 ± 1.2% (mean ± standard deviation) among the men and 4.6 ± 1.0% among the women. This difference in per cent strength was not statistically significant between men and women. In manual muscle testing, the grade of fair for knee extensors is thus very far below the midpoint of the scale from no activity to normal. This means that the good range between grade fair and normal is too wide to connote one particular state of strength. We believe that other methods are needed, for example using a dynamometer, to evaluate intermediate muscle weakness in detail.