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Constant velocity dynamometer: an appraisal using mechanical loading.

D A Murray, E Harrison

    Medicine and Science in Sports and Exercise
    |December 1, 1986
    PubMed
    Summary

    Constant velocity dynamometers like Cybex II require careful calibration. Inertial corrections are crucial for accurate joint torque measurements, especially at higher speeds, to ensure valid muscle function analysis.

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    Area of Science:

    • Biomechanics
    • Human Movement Science
    • Exercise Physiology

    Background:

    • Constant velocity dynamometers are widely used to assess muscle function.
    • Accurate torque measurement is essential for reliable biomechanical analysis.
    • Previous studies have highlighted potential inaccuracies in dynamometer measurements.

    Purpose of the Study:

    • To evaluate the measurement characteristics of Cybex II and Lumex constant velocity dynamometers.
    • To identify sources of error in torque measurements under varying speed and loading conditions.
    • To determine the necessity of inertial corrections for accurate dynamic torque assessment.

    Main Methods:

    • Evaluated two constant velocity dynamometers (Cybex II, Lumex) at 11 speeds (0-5 rad/s).

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  • Utilized a linear accelerometer on the lever arm to measure acceleration.
  • Assessed measurement linearity and validity by regressing observed voltages on expected torques under static and dynamic loading.
  • Calculated inertia-corrected torques to assess their impact on measurement accuracy.

    • Main Results:

    • Dynamometer measurements were linear and valid under static conditions, with greater variance at lower torques.
    • Different calibrations were required for different speed settings, increasing prediction error with higher speeds (% Vfb max).
    • Inertia-corrected torque measurements significantly reduced calibration variability and prediction error.
    • Fluctuations in lever arm velocity were observed due to load and speed interactions with the servomotor.

    Conclusions:

    • Cybex II dynamometers should be calibrated statically.
    • Optimal filtering is recommended to avoid false estimates of joint torque.
    • Inertial corrections are essential to minimize errors from system angular acceleration.
    • Re-assessment of reported muscle function relationships may be necessary given these findings.