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Measuring Knee Extensor Muscle Strength

Bohannon, Richard W., EdD, PT, NCS

American Journal of Physical Medicine & Rehabilitation: January 2001 - Volume 80 - Issue 1 - p 13-18
Research Article: Muscle Testing

Objective To compare manual muscle test with hand-held dynamometer measurements of knee extension strength. A secondary analysis of measurements (n = 256 knees) from 128 acute rehabilitation patients was performed.

Design Knee extensor muscle testing was conducted according to the technique of Hislop and Montgomery; 0 to 5 grades were converted to an expanded 0 to 12 scale. Dynamometry was used to measure the isometric knee extension force with ‘gravity eliminated.‘

Results Manual muscle test and dynamometer measures were highly correlated (r = 0.768;P < 0.001); the correlation was higher when the quadratic nature of the relationship was taken into account (R = 0.887;P < 0.001). Although the dynamometer forces that were associated with different manual muscle test grades differed overall (F = 67.736;P < 0.001), the forces associated with some of the higher grades did not differ statistically.

Conclusions These findings reinforce the convergent construct validity of the manual muscle test and dynamometry measurements but challenge the discriminant construct validity of manual muscle testing. An alternative manual muscle testing grading scheme is suggested that provides for discriminant validity and retains convergent validity.

From the Department of Physical Therapy, School of Allied Health, University of Connecticut, Storrs, Connecticut; and the Institute of Outcomes Research and the Department of Rehabilitation, Hartford Hospital, Hartford, Connecticut.

All correspondence and requests for reprints should be addressed to Richard W. Bohannon, EdD, PT, NCS, Department of Physical Therapy, School of Allied Health, U-101, University of Connecticut, Storrs, CT 06269-2101.

© 2001 Lippincott Williams & Wilkins, Inc.