Anatomical and neuromuscular variables strongly predict maximum knee extension torque in healthy men
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This study examined the relative influence of anatomical and neuromuscular variables on maximal isometric and concentric knee extensor torque and provided a comparative dataset for healthy young males.
Quadriceps cross-sectional area (CSA) and fascicle length (l f) and angle (θ f) from the four quadriceps components; agonist (EMG:M) and antagonist muscle activity, and percent voluntary activation (%VA); patellar tendon moment arm distance (MA) and maximal voluntary isometric and concentric (60° s−1) torques, were measured in 56 men. Linear regression models predicting maximum torque were ranked using Akaike’s Information Criterion (AICc), and Pearson’s correlation coefficients assessed relationships between variables.
The best-fit models explained up to 72 % of the variance in maximal voluntary knee extension torque. The combination of ‘CSA + θ f + EMG:M + %VA’ best predicted maximum isometric torque (R 2 = 72 %, AICc weight = 0.38) and ‘CSA + θ f + MA’ (R 2 = 65 %, AICc weight = 0.21) best predicted maximum concentric torque.
Proximal quadriceps CSA was included in all models rather than the traditionally used mid-muscle CSA. Fascicle angle appeared consistently in all models despite its weak correlation with maximum torque in isolation, emphasising the importance of examining interactions among variables. While muscle activity was important for torque prediction in both contraction modes, MA only strongly influenced maximal concentric torque. These models identify the main sources of inter-individual differences strongly influencing maximal knee extension torque production in healthy men. The comparative dataset allows the identification of potential variables to target (i.e. weaknesses) in individuals.
KeywordsCross-sectional area Fascicle angle Muscle activity Moment arm distance Linear models Strength
Akaike’s information criterion (an information-theoretic approach for model selection)
Akaike’s information criterion for a small dataset
The model's AICc minus the minimum AICc among candidate models
The percentage of times that a given model would be selected as the ‘best-fit model’ by AICc, and serves as the weight of evidence for a given model being the best model from a set of candidate models
Anatomical cross-sectional area
Coefficients of variation
Distal region muscle measurements
Quadriceps EMG amplitude normalised to M-wave amplitude
RF EMG amplitude normalised to RF M-wave amplitude
VL EMG amplitude normalised to VL M-wave amplitude
VM EMG amplitude normalised to VM M-wave amplitude
Average EMG:M ratio of RF, VL and VM
Instantaneous centre of rotation
Intra-class correlation coefficient
Patellar tendon moment arm distance
Maximum peak-to-peak amplitude of the M-wave
Maximal voluntary contraction
Middle region muscle measurements
Maximum muscle compound action potential of vastus lateralis
Physiological cross-sectional area
Proximal region muscle measurements
Root mean square
Range of motion
Maximum voluntary concentric torque
Maximum quadriceps-only concentric torque
Maximum voluntary isometric torque
Maximum quadriceps-only isometric torque
Maximum potentiated twitch torque
Maximum unpotentiated twitch torque
Percent voluntary activation (calculated by interpolated twitch technique)
Funding was provided through the Edith Cowan University post-graduate research scholarship system.
Compliance with ethical standards
Conflict of interest
The authors declare they have no conflict of interest.
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