Search

This study tested whether estimates of persistent inward currents (PICs) in the human plantar flexors would increase with the level of voluntary drive. High-density surface electromyograms were collected from soleus and gastrocnemius medialis of 21 participants (29.2 ± 2.6 yr) during ramp-shaped isometric contractions to 10%, 20%, and 30% (torque rise and decline of 2%/s and 30-s duration) of each participant’s maximal torque. Motor units identified in all the contraction intensities were included in the paired-motor unit analysis to calculate delta frequency (DF) and estimate the PICs. DF is the difference in discharge rate of the control unit at the time of recruitment and derecruitment of the test unit. Increases in PICs were observed from 10% to 20% [D = 0.6 pulse per second (pps); P < 0.001] and from 20% to 30% (D = 0.5 pps; P < 0.001) in soleus and from 10% to 20% (D = 1.2 pps; P < 0.001) but not from 20% to 30% (D = 0.09 pps; P = 0.724) in gastrocnemius medialis. Maximal discharge rate increased for soleus and gastrocnemius medialis from 10% to 20% [D = 1.75 pps (P < 0.001) and D = 2.43 pps (P < 0.001), respectively] and from 20% to 30% [D = 0.80 pps (P < 0.017) and D = 0.92 pps (P = 0.002), respectively]. The repeated-measures correlation identified associations between DF and increases in maximal discharge rate for soleus (r = 0.64; P < 0.001) and gastrocnemius medialis (r = 0.77; P < 0.001). An increase in voluntary drive tends to increase PIC strength, which has key implications for the control of force but also for comparisons between muscles or studies when relative force levels might be different. Increases in voluntary descending drive amplify PICs in humans and provide an important spinal mechanism for motor unit discharging, and thus force output modulation. NEW & NOTEWORTHY Animal experiments and computational models have shown that motor neurons can amplify the synaptic input they receive via persistent inward currents. Here we show in huma

The quantification of maximal mean speed (MMS), maximal mean metabolic power (MMP met), critical speed (CS) and critical metabolic power (CP met) was conducted over full A-League (elite) and National Premier League (NPL; sub-elite) seasons. Comparisons were made between levels of soccer competition and playing positions (i. e. centre backs, full backs, central midfielders, wide midfielders and strikers). A symmetric moving average algorithm was applied to the GPS raw data using specific time windows (i. e. 1, 5, 10, 60, 300 and 600 s) and maximal values were obtained. Additionally, these maximal values were used to derive estimates of CS and CP met. Maximal mean values, particularly during smaller time windows (i. e. 1 and 5 s), were greater in A-League match play. Only MMP met1 was identified as being consistently different between competitions (P = < 0.001 – 0.049) in all playing positions. Significance was only observed in CS (P = 0.005) and CP met (P = 0.005) of centre backs between competitions. Centre backs were identified as the least energy demanding playing position. The present findings suggests that both maximal mean and critical analyses are suitable alternatives to common absolute distance and speed assessments of match running performance during competitive matches. © 2020 Georg Thieme Verlag KG StuttgartNew York.

Lord, C., Blazevich, A. J., Abbiss, C. R., & Maʼayah, F. (2020). A reduction in match-to-match variability using maximal mean analyses in sub-elite soccer. International Journal of Sports Medicine, 41(05), 300-305. https://doi.org/10.1055/a-1073-7851

Kay, A. D., Blazevich, A. J., Fraser, M., Ashmore, L., & Hill, M. W. (2020). Isokinetic eccentric exercise substantially improves mobility, muscle strength and size, but not postural sway metrics in older adults, with limited regression observed following a detraining period. European Journal of Applied Physiology, 1-13. https://doi.org/10.1007/s00421-020-04466-7

Pinto, M. D., Wilson, C., Kay, A. D., Cochrane, J., & Blazevich, A. J. (2019). The effect of isokinetic dynamometer deceleration phase on maximum ankle joint range of motion and plantar flexor mechanical properties tested at different angular velocities. Journal of Biomechanics, 92, 169–174. Available here

Trezise, J., Collier, N., & Blazevich, A. J. (2016). Anatomical and neuromuscular variables strongly predict maximum knee extension torque in healthy men. European journal of applied physiology, 116(6), 1159-1177. Available here