Method-related variations in estimates of gravity correction values using electromechanical dynamometry

A knee extension study

J. L. Keating, T. A. Matyas

Research output: Contribution to journalArticleResearchpeer-review

10 Citations (Scopus)

Abstract

Dynamometry is widely used to measure subject strength. The method employed to correct dynamometry scores for gravitational influences can result in differing correction estimates. This study investigates differences between mathematical estimates of correction values and directly measured passive tortes. Using the Kin-Com dynamometer, passive force measurements from 90° of knee flexion to full extension were collected for nine asymptomatic subjects. These measurements were then compared with correction estimates mathematically extrapolated from a force reading obtained at one point in the test range. Direct passive measurements obtained between 0 and 70° of knee flexion and mathematical estimations of correction values differed by as much as 50 N. The equivalence of gravity correction values obtained using the two methods detailed cannot be assumed. Mathematical estimates of correction values for knee scores obtained between 0 and 90° of flexion were found to be clinically identical to direct passive measurements when: 1) the limb was weighed close to 50° of flexion and 2) the angular location of the lower limb mass relative to the horizontal was not assumed to be represented by the angular location of the lever arm, but rather 15° further below the horizontal than the lever arm.

Original languageEnglish
Pages (from-to)142-453
Number of pages312
JournalJournal of Orthopaedic and Sports Physical Therapy
Volume24
Issue number3
Publication statusPublished - 3 Sep 1996

Keywords

  • correction for segment weight
  • measurement
  • muscle strength

Cite this

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abstract = "Dynamometry is widely used to measure subject strength. The method employed to correct dynamometry scores for gravitational influences can result in differing correction estimates. This study investigates differences between mathematical estimates of correction values and directly measured passive tortes. Using the Kin-Com dynamometer, passive force measurements from 90° of knee flexion to full extension were collected for nine asymptomatic subjects. These measurements were then compared with correction estimates mathematically extrapolated from a force reading obtained at one point in the test range. Direct passive measurements obtained between 0 and 70° of knee flexion and mathematical estimations of correction values differed by as much as 50 N. The equivalence of gravity correction values obtained using the two methods detailed cannot be assumed. Mathematical estimates of correction values for knee scores obtained between 0 and 90° of flexion were found to be clinically identical to direct passive measurements when: 1) the limb was weighed close to 50° of flexion and 2) the angular location of the lower limb mass relative to the horizontal was not assumed to be represented by the angular location of the lever arm, but rather 15° further below the horizontal than the lever arm.",
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Method-related variations in estimates of gravity correction values using electromechanical dynamometry : A knee extension study. / Keating, J. L.; Matyas, T. A.

In: Journal of Orthopaedic and Sports Physical Therapy, Vol. 24, No. 3, 03.09.1996, p. 142-453.

Research output: Contribution to journalArticleResearchpeer-review

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AU - Keating, J. L.

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N2 - Dynamometry is widely used to measure subject strength. The method employed to correct dynamometry scores for gravitational influences can result in differing correction estimates. This study investigates differences between mathematical estimates of correction values and directly measured passive tortes. Using the Kin-Com dynamometer, passive force measurements from 90° of knee flexion to full extension were collected for nine asymptomatic subjects. These measurements were then compared with correction estimates mathematically extrapolated from a force reading obtained at one point in the test range. Direct passive measurements obtained between 0 and 70° of knee flexion and mathematical estimations of correction values differed by as much as 50 N. The equivalence of gravity correction values obtained using the two methods detailed cannot be assumed. Mathematical estimates of correction values for knee scores obtained between 0 and 90° of flexion were found to be clinically identical to direct passive measurements when: 1) the limb was weighed close to 50° of flexion and 2) the angular location of the lower limb mass relative to the horizontal was not assumed to be represented by the angular location of the lever arm, but rather 15° further below the horizontal than the lever arm.

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