Author(s): GROSSIO, L., SALVAGGIO, F., BERBENNI, T., SAMOZINO, P., RAINOLDI, A., BOCCIA, G., Institution: UNIVERSITY OF TURIN, Country: ITALY, Abstract-ID: 2210

INTRODUCTION:
Despite their widespread use in practice, the impact of velocity loss thresholds on the neuromuscular system remains largely unexplored. The aim of this study is therefore to characterise the effects of different magnitudes of velocity loss on explosive force production and central/peripheral fatigability.
METHODS:
Thirty-one young male athletes (15 endurance and 16 resistance-based) performed, on a single leg knee extension, three sets at 70% of 1-RM conducted to different levels of velocity loss targets (10-20-40%). Mean propulsive velocity (MPV), peak torque and rate of torque development (RTDpeak) were continuously recorded during the sets, as were vastus lateralis and medialis high-density surface electromyography (HD-sEMG).
Baseline and post-sets supramaximal stimuli (singles and octets) were delivered to peripheral nerve to assess sarcolemma excitability, contractile properties, and neural efficacy (i.e. voluntary/evoked impulse ratio), as well as to normalise EMG root mean square (RMS) of the first 150 ms of contraction.
RESULTS:
A reduction of peak torque (Cohen’s d = 0.88, p < 0.05) was associated with 10% of velocity loss whereas higher velocity loss thresholds were required to affect RTDpeak (Cohen’s d = 0.79 - 1.72, p < 0.05) and induce neuromuscular fatigability. Muscle activation (Cohen's d = 1.16, p < 0.05), contractile properties (Cohen’s d = 1.17, p < 0.05) and neural efficacy (Cohen’s d = 1.87, p < 0.001) decreased significantly already at 20% velocity loss in resistance-based participants while endurance athletes exhibited signs of central fatigability at 40% velocity loss with reductions of RMS (Cohen’s d = 1.17, p < 0.05) and neural efficacy (Cohen’s d = 2.07, p < 0.001). In both groups M-wave peak to peak amplitude decreased significantly at 40% of velocity loss (Cohen’s d = 0.52, p < 0.05).
CONCLUSION:
The findings on neuromuscular fatigability suggest that, while a 10% loss in velocity preserves explosive force capacity and neuromuscular function, higher thresholds induce different central and peripheral costs depending on the athlete's training background. Therefore, the percentage of load and velocity loss should be personalized considering the critical torque/power of the athlete.