Comparison of the Dynamometer- and Kinematics-based Analyses for Measuring Individual Quadriceps Muscle Torque: A Pilot Study

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Background.Current studies on exercise-induced injury effects lack direct force measurements of individual agonist muscles post-injury, relying on indirect markers.Transcutaneous muscle stimulation assesses the intrinsic forceproducing capacity of the entire muscle group but has not been used to compare individual muscle strength.Objectives.Compare the reliability of dynamometer-based and kinematic-based methods in measuring the torque produced by electrical stimulation of individual quadriceps muscles.Methods.Eight males (30.3±3.9 years) were enrolled for a two-day test-retest study.On Day 1, peak isometric torque during maximal voluntary contractions (MVC) was assessed, followed by peak isometric tetanic torque produced by electrical stimulation (20 & 80 Hz) of the vastus medialis, rectus femoris, and vastus lateralis muscles using the Biodex dynamometer with the knee at 90° and the shin pad 2 cm above the lateral malleolus.Subjects performed two MVCs for four seconds each.Isometric torque during 20 and 80 Hz stimulations of the individual quadriceps muscles was then recorded by the dynamometer.The kinematics of the weighted leg during 20 and 80 Hz electrical stimulation-induced concentric contractions targeting the individual muscles were collected by a motion capture system (Vicon) to calculate peak torque.Procedures were repeated within seven days.Test-retest reliability was analyzed using intraclass correlation coefficients (ICC) and Bland-Altman plots.Results.Both methods showed strong test-retest reliability (Biodex ICC=0.95[95% CI: 0.90-0.97];Vicon ICC=0.98 [95% CI: 0.96-0.98]).The reliability of both methods was further supported by the Bland-Altman plot.Conclusion.Dynamometer-and kinematics-based analyses were reliable for measuring individual quadricep muscle torque produced by transcutaneous electrical stimulation.