No abstract

The aim of this study was to establish how well a three-parameter sigmoid exponential function, DIFACT, follows experimentally obtained voluntary neural activation-angular velocity profiles and how robust it is to perturbed levels of maximal activation. Six male volunteers (age 26.3 ± 2.73 years) were tested before and after an 8-session, 3-week training protocol. Torque-angular velocity (T-ω) and experimental voluntary neural drive-angular velocity (%VA-ω) datasets, obtained via the interpolated twitch technique, were determined from pre-and post-training testing sessions. Non-linear regression fits of the product of DIFACT and a Hill type tetanic toque function and of the DIFACT function only were performed on the pre-and post-training T-ω and %VA-ω datasets for three different values of the DIFACT upper bound, α max , 100%, 95% & 90%. The determination coefficients, R 2 , and the RMS of the fits were compared using a two way mixed ANOVA and results showed that there was no significant difference (p < 0.05) due to changing α max values indicating the DIFACT remains robust to changes in maximal activation. Mean R 2 values of 0.95 and 0.96 for pre-and post-training sessions show that the maximal voluntary torque function successfully reproduces the T-ω raw dataset.

The hamstring to quadriceps (H : Q) strength ratio is widely used to identify individuals at risk of sustaining hamstring strain injuries. However, its efficacy is not supported by the current evidence. Current methods for the calculation of the H : Q ratio provide only a one- or two-dimensional ratio, often ignoring fundamental muscle mechanical properties. Based on isokinetic torque measurements of the knee flexors and extensors (0–400° s −1 ) in 25 young, physically active males, we derived a model equation that creates a three-dimensional H : Q functional ratio profile. The model robustness was tested against a different number of input torque data (8, 11, 14 and 17 pairs of points) and small perturbation of the knee joint angle data (5°). The model was consistent and behaved well under all conditions apart from the eight pairs of points ( R 2 = 0.84−0.96; RMSE = 0.14−0.25; NRMSE = 0.12−0.27), and the H : Q functional ratio was successfully described even at angles and velocities that cannot be normally assessed with isokinetic dynamometry. Overall, our results suggest that the model can provide a fast and accurate three-dimensional description of the knee joint muscle strength balance using as few as 11 experimental data points and this could be an easy-to-employ screening tool.

Despite full voluntary effort, neuromuscular activation of the quadriceps group of muscles appears inhibited during eccentric contractions. A nerve stimulation protocol during dynamic contractions of the quadriceps was developed that employed triplets of supramaximal pulses to assess suppressed eccentric activation. Subsequently the effects of a short training intervention, performed on a dynamometer, on eccentric strength output and neural inhibition were examined. Torque-angular velocity (T-ω) and experimental voluntary neural drive-angular velocity (%VA-ω; %VA, obtained via the interpolated twitch technique) datasets, were obtained from pre- and post-training testing sessions. Non-linear regression fits of a seven parameter torque function and of a 3rd degree polynomial were performed on the pre- and post-training T-ω and %VA-ω datasets respectively. T-test showed a significant (p < 0.05) increase in the overall torque output post-training for the group, with three out of the six subjects demonstrating a significant (p < 0.05) increase in the torque output across the range of angular velocities as shown by the extra-sum-of-squares F-test. A significant increase (p < 0.05) in the %VA post-training was also observed as well as a reduction in the plateauing of the torque output during fast eccentric contractions.