Reproducibility of isokinetic strength assessment of knee muscle actions in adult athletes: Torques and antagonist-agonist ratios derived at the same angle position.

João P Duarte,André Seabra,Manuel J Coelho-E-Silva,Joana Rosado,Rui S Gonçalves,Edilson S Cyrino,João Valente-Dos-Santos,Jorge Conde,Pedro Couto,Diogo Martinho,Daniela Costa

doi:10.1371/journal.pone.0202261

Abstract

The current study aimed to examine the reliability of the conventional and functional ratios derived from peak torques (PTs) and those obtained from the combination of knee flexors torque at the angle of knee extensors PT. Twenty-six male athletes (mean of 24.0±0.7 years) from different sports completed a test-to-test variation in isokinetic strength (Biodex, System 3) within a period of one week. Anthropometry and body composition assessed by Dual Energy X-ray Absorptiometry were also measured. The proposed isokinetic strength ratio measurements appeared to be highly reliable: conventional ratio at PT angle (intra-class correlation, ICC = 0.98; 95% confidence interval; 95%CI: 0.95 to 0.99); functional extension ratio at PT angle (ICC = 0.98; 95%CI: 0.96 to 0.99); and, functional flexion ratio at PT angle (ICC = 0.95; 95%CI: 0.89 to 0.98). Technical error of measurement (TEM) and associated percentage of the coefficient of variation (%CV) were as follows: conventional ratio at PT angle (TEM = 0.02; %CV = 4.1); functional extension ratio at PT angle (TEM = 0.02; %CV = 3.8); and, functional flexion ratio at PT angle (TEM = 0.03; %CV = 3.6). The current study demonstrated that the traditional and new obtained simple and combined isokinetic indicators seem highly reliable to assess muscle strength and function in adult male athletes. A single testing session seems to be sufficiently to obtain these isokinetic strength indicators.

Highlights

The terms muscle strength and muscle power are erroneously used as synonymous in many professional contexts
The angular velocity is kept constant by the dynamometer that adjusts the resistance applied to the muscles through the range of motion
The antagonist-agonist strength relationship should be interpreted at the specific angle, at the angle of the agonist Peak torque (PT). Because of these data quality properties are of utmost importance in the evaluation of athletes, the purpose of the current study was to examine the reliability of the conventional and functional ratios derived from PTs and those obtained from the combination of knee flexors (KF) torque at the angle of knee extensors (KE) PT

Summary

Introduction

The terms muscle strength and muscle power are erroneously used as synonymous in many professional contexts. The term ‘muscular strength’ refers to maximal muscular force in a single voluntary contraction [1]. The relationship between the torque exerted by a muscle group and the range of motion of the joint is determined by mechanical characteristics of the anatomical lever system. In many muscle actions, such as knee extension and knee flexion, the mechanical disadvantage of the muscles occurs at the extremes of the range of motion. Isokinetic refers to dynamic muscular contraction characterized by a constant angular velocity of the movement [2, 3]. The angular velocity is kept constant by the dynamometer that adjusts the resistance applied to the muscles through the range of motion (i.e. the load applied to the muscle is increased at the point of highest mechanical advantage of the muscle and, correspondingly, the load is decreased at the extremes of the range of motion)

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