Was Torque Measured?

To the Editor:

We read with interest the article by Daubney and Culham entitled "Lower-Extremity Muscle Force and Balance Performance in Adults Aged 65 Years and Older" in the December 1999 issue. We generally found the work of interest and quite commendable, with one exception. In the article, the authors indicate that they measured force via a dynamometer, reporting these values as being measured at a location "just proximal" to various bony landmarks or joints. As it is well known that the measured forces vary as a function of the distance of the force-measuring device from the axis joint rotation, the method--and meaningfulness for others--would be more appropriate if the precise distance were recorded and the torque calculated. The fact that the height of the subjects varied from 153 to 192 cm ensures that the distances were different.

Thus, in works such as this and the normative data published by Andrews et al,[1] clinicians and investigators should record the force and the perpendicular distance to the joint axis and calculate torque, preferably in units of newton-meters. Unless torque is measured, comparability across patients is not possible because the same joint torque is measured by dynamometry at different locations, yielding entirely different force values. Using something other than torque data does not meet the measurement standards we need in our practice.

Gary L Soderberg, PT, PhD, FAPTA
Professor
Physical Therapy
Southwest Missouri State University
Springfield, MO 65804
([e-mail])

Susan Robinson, PT, DPT
Assistant Professor
Physical Therapy
Southwest Missouri State University
([e-mail])

References

[1] Andrews AW, Thomas MW, Bohannon RW. Normative values for isometric muscle force measurements obtained with hand-held dynamometers. Phys Ther. 1996;76:248-259.

Author Response:

We appreciate Dr Soderberg's and Dr Robinson's comments regarding our article. We chose to measure force to allow comparison with data from previous studies that used handheld dynamometry to measure muscle force. Because there was no difference in height between subjects in the 2 groups, the comparison of force values was appropriate in our study. However, we agree that it would have been preferable to measure the distance from joint axis to point of dynamometer application and report torque rather than force values. Torque values are more meaningful and allow more accurate comparison between subjects. Unfortunately, we did not measure the distance and could not calculate torque values. We will certainly do so in future studies.

Elsie G Culham, PT, PhD Associate Professor Physical Therapy Program School of Rehabilitation Therapy Queen's University Kingston, Ontario, Canada K7L 3N6 ([e-mail])

Marguerite Elizabeth Daubney, PT, MSc

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