Abstract
The aim of this paper was to outline a multilevel modeling approach to fit individual angle-specific torque curves describing concentric knee extension and flexion isokinetic muscular actions in Master athletes. The potential of the analytical approach to examine between individual differences across the angle-specific torque curves was illustrated including between-individuals variation due to gender differences at a higher level. Torques in concentric muscular actions of knee extension and knee extension at 60º·s−1 were considered within a range of motion between 5º and 85º (only torques “truly” isokinetic). Multilevel time series models with autoregressive covariance structures with standard multilevel models were superior fits compared with standard multilevel models for repeated measures to fit angle-specific torque curves. Third and fourth order polynomial models were the best fits to describe angle-specific torque curves of isokinetic knee flexion and extension concentric actions, respectively. The fixed exponents allow interpretations for initial acceleration, the angle at peak torque and the decrement of torque after peak torque. Also, the multilevel models were flexible to illustrate the influence of gender differences on the shape of torque throughout the range of motion and in the shape of the curves. The presented multilevel regression models may afford a general framework to examine angle-specific moment curves by isokinetic dynamometry, and add to the understanding mechanisms of strength development, particularly the force-length relationship, both related to performance and injury prevention.
Highlights
Physiological functions during exercise, generally used to describe populations, compare groups or define changes across the life span, are all conceptualized in respect to time (Rowland, 2011)
Smaller value of Akaike's Information Criterion (AIC) and Bayesian Information Criterion (BIC) for the third degree polynomial model implies that this model was a better fit compared to the second degree polynomial model and fourth degree polynomial model to fit the anglespecific torque curves of isokinetic knee extension (KE) action
Multilevel time series models with autoregressive covariance structures with standard multilevel models had substantially lower AIC and BIC compared with standard multilevel models for repeated measures to fit angle-specific torque curves
Summary
Physiological functions during exercise, generally used to describe populations, compare groups or define changes across the life span, are all conceptualized in respect to time (Rowland, 2011). The shape of the curves has been mostly described using maximal voluntary muscular action under isometric conditions (Herzog et al, 1991; Philippou et al, 2004, 2012). Isokinetic dynamometry has emerged as a favoured method both in clinical research and applied sports contexts to provide information about maximal dynamic muscular action when the velocity of the movement is controlled and maintained constant (Gleeson and Mercer, 1996; Tsepis et al, 2004). The importance of interpreting the profile of isokinetic anglespecific moment curves between the injured (such as anterior cruciate ligament) and healthy lower limb is recognized (Tsepis et al, 2004), but seldom reported and limited to case studies. It is important to consider acute shifts in the forcelength relationship as consequence of muscle-
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