Date of Award
Edith Cowan University
Doctor of Philosophy
School of Exercise and Health Sciences
Faculty of Health, Engineering and Science
Associate Professor Anthony Blazevich
The present research aimed to determine (i) the relative influence anatomical and neuromuscular variables on maximal isometric, concentric and eccentric knee extensor torque (Study 1); (ii) whether the change in strength following a 10-week strength training program is associated with changes in specific anatomical and neuromuscular variables (Study 2a); (iii) whether anatomical and neuromuscular adaptations are dependent on their pre-training magnitudes; and (iv) whether it is possible to ‘predict’ an individual’s adaptation to strength training based on their anatomical and neuromuscular pre-training magnitudes (Study 2b).
The variables assessed throughout the studies include muscle cross-sectional area (CSA), fascicle length and angle from the proximal, middle and distal regions of the four quadriceps components; agonist (EMG:Mwave) and antagonist (EMG normalised to MVC) muscle activity, percent voluntary activation (%VA; interpolated twitch technique); maximum isometric and slow speed concentric and eccentric (60°/s), unpotentiated and potentiated twitch torques; and patella tendon moment arm distance.
Using a cross-sectional (observational) study design (Study 1; n = 56) models incorporating CSA, fascicle angle and muscle activity and activation were found to best predict both maximum isometric and eccentric torque (R2 = 0.72 and 0.62). Maximum concentric torque was best predicted by a model incorporating CSA, fascicle angle and moment arm (R2 = 0.64) making it suitable for predicting maximal torque in clinical/rehabilitation populations. Proximal CSA was included in the strongest models rather than the traditionally used mid-muscle CSA, indicating its potential functional importance. The strong predictive ability of models incorporating both CSA and fascicle angle indicate that the quantity of contractile tissue strongly influences inter-individual differences in strength expression.
Following 10 weeks of heavy lower-limb heavy strength training (Study 2a; n = 36), the change in isometric torque was best (although weakly; R2 = 0.27) predicted by models incorporating the change in proximal-region vastus lateralis CSA and fascicle angle, and changes in concentric and eccentric torque were best predicted by average quadriceps muscle activity, proximal-region CSA (either vastus lateralis or whole quadriceps) and vastus intermedius fascicle angle (R2 = 0.40 and 0.41). Changes in fascicle angle were weakly correlated with the change in strength despite its inclusion in the strongest models, highlighting the requirement to examine interactions between variables when assessing their influence on strength change. Furthermore, the weak relationships observed between the change in strength and the change in neuromuscular variables (Study 2a) indicate that the assumption that simultaneous changes observed in strength, anatomical structure and neuromuscular function following training indicate potential causal association may need to be reconsidered.
While muscle activation measured pre-training during isometric contractions was moderately and negatively correlated with the strength change following training (Study 2b), there was no correlation for proximal-region CSA. This indicated limited scope for improvement in activation isometrically in individuals with greater levels of activation prior to training, but that all individuals had similar scope for hypertrophy. It was not possible to predict the strength change elicited by training from the measurements obtained before training (R2 = 0.06 to 0.27).
A comparative data set presented in Study 1 provides clinicians with a tool to evaluate an individual’s maximum torque capacity, anatomical structure and neuromuscular function. While accurate prediction of strength change following training cannot be made based on pre-training testing using the current protocols (Study 2b), strength training programs targeted to improve muscle activation (Study 2a) might elicit the greatest improvements in concentric and eccentric knee extensor strength.
Trezise, J. C. (2014). Relative importance and plasticity of anatomical and neuromuscular factors affecting joint torque production. Edith Cowan University. Retrieved from https://ro.ecu.edu.au/theses/1407