The purpose of this study was to evaluate the evolution of jump and sprint force‐production capacities with maturation in young soccer players. One hundred sixteen young elite male soccer players aged 11–17 years were assigned to six different groups according to their maturity status. The force–velocity (F–V) profiles in jumping and sprinting performances were compared among groups. The results show a significant, progressive, and linear improvement in the majority of F–V profile determinants of jumping and sprinting performances in parallel with maturation. When comparisons were carried out between consecutive groups, significant differences between PHV−1 and PHV groups in H_max (p < 0.05), H₆₀ (p < 0.05), VT‐F0 (p < 0.05), and VT‐P_max (p < 0.05) were observed but disappeared when these variables were expressed relative to body mass. Regarding the F–V profile determinants of sprinting performance, we observed significantly shorter sprint times in PHV compared to PHV−1 and in PHV+2 in comparison with the PHV+1 group. These between‐group differences were associated with significant greater HZT‐F0 kg⁻¹ (p < 0.05) and HZT‐P_max kg⁻¹ (p < 0.001). However, significantly more negative value of HZT‐Sfv kg⁻¹ was observed in PHV−1 compared to PHV−2 (p < 0.05), in PHV+1 in comparison with PHV (p < 0.05) and in PHV+3 when compared to the PHV+2 group (p < 0.05). Thus, these findings revealed an alternation of accelerated periods of development in force and velocity qualities, expressing sprinting performance, with maturation during the physical development process of young soccer players. Trainers and coaches should be aware of the distinct mechanical characteristics related to each maturity stage and design specific programs accordingly.

Background: Exercise capacity is markedly impaired in patients with end-stage renal disease (ESRD) due to neuromuscular dysfunction and reduced oxygen delivery. This study aimed to investigate the effects of NMES during HD on exercise capacity in patients with ESRD. It specifically examined neuromuscular and hemodynamic adaptations. Methods: Twenty-two patients with ESRD were randomized to a neuromuscular electrical stimulation training group (NSTG, n = 11) or a control group (CG, n = 11). The NSTG underwent intradialytic quadriceps NMES three times per week for 12 weeks (40 min/session). Exercise capacity was evaluated via sustained isometric contraction at 50% of maximal voluntary contraction (MVC) until exhaustion. Neuromuscular function was assessed through voluntary activation (ΔVA) and potentiated twitch force (ΔQ_tw,pot), while muscle oxygenation (ΔO₂Hb, ΔHHb, ΔTHb) of the vastus lateralis was continuously monitored using near-infrared spectroscopy. Results: After the intervention, the NSTG showed a significant +20% increase in Tlim (103.9 ± 14.4 s to 123.3 ± 16.6 s; p = 0.01) and +30% improvement in MVC (421.3 ± 24.9 N to 550.4 ± 20.3 N; p < 0.01), while no improvements were observed in CG. Resting VA increased by ≈7% in NSTG (90.2 ± 3.7% to 96.8 ± 2.5%; p = 0.012). Improved muscle oxygenation and reduced twitch force suggest enhanced oxidative capacity and greater peripheral fatigue tolerance. Conclusions: Intradialytic NMES elicited robust improvements in exercise capacity, muscle strength, and oxygen utilization in ESRD patients by enhancing both central activation and peripheral oxidative adaptations. These findings support NMES as a feasible and effective rehabilitative strategy to counteract fatigue and functional decline in the ESRD population.

The aim of the present study was to assess the effect of beetroot juice supplementation (BEET) on neuromuscular fatigue etiology during simulated soccer match play. In a randomized, double-blind, crossover design, 13 soccer players completed the Loughborough Intermittent Shuttle Test (LIST). Players received either BEET (2×150 mL; ∼8 mmol/L nitrate) or placebo (PLA) for 7 days (6 days prior to the experimental session and on the day of trial, 2 h before LIST). Neuromuscular assessments were performed at baseline, 45 min (half time: HT), and 90 min (full time: FT) following LIST. Maximal voluntary contraction (MVC) and twitch responses, delivered through electrical femoral nerve stimulation, were used to assess peripheral (quadriceps resting twitch force Q_tw,pot) and central fatigue (voluntary activation, VA). Compared with baseline, MVC Q_tw,pot and VA values decreased in PLA and BEET conditions at HT and FT ( P < 0.05). Compared with PLA, the decrease in MVC and Q_tw,pot was significantly attenuated with BEET at HT and FT ( P < 0.001). Likewise, BEET attenuated the decrease in VA at HT ( P < 0.001, d = 1.3) and FT ( P < 0.001, d = 1.5) compared with the PLA condition. Chronic beetroot juice supplementation attenuates neuromuscular fatigue development during simulated soccer matches, and this is due to both central and peripheral factors. Consequently, chronic beetroot may optimize physical performance.

This study investigated the etiology of neuromuscular fatigue induced by a 5-m shuttle run test (5MSRT) in soccer players. Nineteen adult male amateur soccer players (age: 20.0 ± 2.9 years) participated in the present study. Before and after the 5MSRT, they were instructed to complete a maximal voluntary isometric contraction (MVIC) of the knee extensors (KE) during and after which two electrical stimulations were applied at the femoral nerve. Voluntary activation level (VAL), surface electromyography recordings (sEMG), electrophysiological (Mmax) and potentiated resting twitch (Ptw) responses of the KE were compared between pre- and post-5MSRT. Rating of perception exertion (RPE) was also assessed before, during the test immediately following each sprint repetition and after the test. The distance covered during each sprint significantly decreased as the number of trials performed increased (p<.05). The RPE reported following each sprint significantly increased throughout the test. In addition, MVIC (-9%), sEMG (-23%), VAL (-15%), Ptw (-26%) and Mmax (~22%) of the KE were lowered from pre-to-post 5MSRT (.001 < p < .01). The 5MSRT induced a decrease of repeated-sprint running performance and MVIC of the KE. These decrements were accompanied by lowered VAL, sEMG, Ptw and Mmax values of the KE reflecting the involvement of both the central and peripheral origins in the 5MSRT-induced fatigue. Given the important muscle stress induced by 5MSRT, this strenuous test must be applied with caution, after an inevitable familiarization phase, and not during the competition period to avoid the risk of serious injury.