Factors Influencing Manual Muscle Tests in Physical Therapy: The Magnitude and Duration of Force Applied

James A. Nicholas, M.D., Alexander Sapega, B.A., A.T.C., Harry Kraus, Ph.D., and Joseph N. Webb, R.P.T., New York, N.Y.

From the Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York City

To determine whether it is the amount or the duration of the force applied manually by the tester, or both, that determines the tester's perception of the strength of the hip flexor or abductor muscles, an electromechanical device was designed which was placed between the tester's hand and the subject's limb. With the device we measured the force applied to the limb, the time interval during which it was applied, and the angular position of the limb during the entire test. In 240 such tests, the testers' ratings of the differences in strength between the right and left sides were correlated with seven variables involving force and time. It was found statistically that the impulse-that is, the duration of the tester's effort multiplied by the average applied force during each test-was the factor that most influenced the tester in the ratings.

The Journal of Bone and Joint Surgery, Vol. 60-A, No. 2, pp. 186-190, March 1978