Explore the vast range of titles available.

Exercise-induced fatigue causes changes within the central nervous system that decrease force production capacity in fatigued muscles. The impact on unrelated, non-exercised muscle performance is still unclear. The primary aim of this study was to examine the impact of a bilateral forearm muscle contraction on the motor function of the distal and unrelated ankle plantar-flexor muscles. The secondary aim was to compare the impact of maximal and submaximal forearm contractions on the non-fatigued ankle plantar-flexor muscles. Maximal voluntary contractions (MVC) of the forearm and ankle plantar-flexor muscles as well as voluntary activation (VA) and twitch torque of the ankle plantar-flexor muscles were assessed pre-fatigue and throughout a 10-min recovery period. Maximal (100 % MVC) and submaximal (30 % MVC) sustained isometric handgrip contractions caused a decreased handgrip MVC (to 49.3 ± 15.4 and 45.4 ± 11.4 % of the initial MVC for maximal and submaximal contraction, respectively) that remained throughout the 10-min recovery period. The fatigue protocols also caused a decreased ankle plantar-flexor MVC (to 77 ± 8.3 and 92.4 ± 6.2 % of pre-fatigue MVC for maximal and submaximal contraction, respectively) and VA (to 84.3 ± 15.7 and 97.7 ± 16.1 % of pre-fatigue VA for maximal and submaximal contraction, respectively). These results suggest central fatigue created by the fatiguing handgrip contraction translated to the performance of the non-exercised ankle muscles. Our results also show that the maximal fatigue protocol affected ankle plantar-flexor MVC and VA more severely than the submaximal protocol, highlighting the task-specificity of neuromuscular fatigue.

IntroductionThe application of blood flow restriction (BFR) to low-intensity exercise may be able to increase strength not only in the trained limb but also in the homologous untrained limb. Whether this effect is repeatable and how that change compares to that observed with higher intensity exercise is unknown.PurposeExamine whether low-intensity training with BFR enhances the cross-education of strength compared to exercise without BFR and maximal efforts.MethodsA total of 179 participants completed the 6-week study, with 135 individuals performing isometric handgrip training over 18 sessions. Participants were randomly assigned to one of four groups: 1) low-intensity (4 × 2 min of 30% MVC; LI, n = 47), 2) low-intensity with blood flow restriction (LI + 50% arterial occlusion pressure; LI-BFR, n = 41), 3) maximal effort (4 × 5 s of 100% MVC; MAX, n = 47), and 4) non-exercise control (CON, n = 44).ResultsLI-BFR was the only group that observed a cross-education in strength (CON: 0.64 SD 2.9 kg, LI: 0.95 SD 3.6 kg, BFR-LI: 2.7 SD 3.3 kg, MAX: 0.80 SD 3.1 kg). In the trained hand, MAX observed the greatest change in strength (4.8 SD 3.3 kg) followed by LI-BFR (2.8 SD 4.0 kg). LI was not different from CON. Muscle thickness did not change in the untrained arm, but ulna muscle thickness was increased within the trained arm of the LI-BFR group (0.06 SD 0.11 cm).ConclusionIncorporating BFR into low-intensity isometric training led to a cross-education effect on strength that was greater than all other groups (including high-intensity training).

PurposeThe purpose of the study was to investigate the effects of using a vibration foam roll (VFR) or a non-vibration foam roll (NVFR) on maximum voluntary isometric contraction peak torque (MVIC), range of motion (ROM), passive resistive torque (PRT), and shear modulus.MethodsTwenty-one male volunteers visited the laboratory on two separate days and were randomly assigned to either a VFR group or a NVFR group. Both interventions were performed for 3 × 1 min each. Before and after each intervention, passive resistive torque and maximum voluntary isometric contraction peak torque of the leg extensors were assessed with a dynamometer. Hip extension ROM was assessed using a modified Thomas test with 3D-motion caption. Muscle shear modulus of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was assessed with shear wave elastography (SWE).ResultsIn both groups (VFR, NVFR) we observed an increase in MVIC peak torque (+ 14.2 Nm, + 8.6 Nm) and a decrease in shear modulus of the RF (− 7.2 kPa, − 4.7 kPa). However, an increase in hip extension ROM (3.3°) was only observed in the VFR group. There was no change in PRT and shear modulus of the VL and VM, in both the VFR group and the NVFR group. Our findings demonstrate a muscle-specific acute decrease in passive RF stiffness after VFR and NVFR, with an effect on joint flexibility found only after VFR.ConclusionThe findings of this study suggest that VFR might be a more efficient approach to maximize performance in sports with flexibility demands.

The principle of gradual overload is crucial in improving sports performance, yet the effects of combining speed and weight overloads in plyometric training remain understudied. This study investigated the effects of plyometric training with speed and weight overloads on isokinetic strength, explosive power, and agility in volleyball players. Forty male volleyball players were randomly assigned to four groups: plyometric training (PT), plyometric training with speed overload (PTS), plyometric training with weight overload (PTW), and plyometric training with both speed and weight overload (PTSW). Each group completed a four-week plyometric training regimen. Performance metrics, including Sarjent's jump height (SJH), Spike jump height (SPJH), Sheppard test (ShT), muscle voluntary isometric contraction (MVIC), rate of force development (RFD), absolute peak torque (PTQ), relative peak torque (RPT), and average power (AP) of knee extensors and flexors were measured before and after the intervention. SJH improved significantly in PTS (P = 0.012), PTW (P = 0.041), and PTSW (P = 0.001) compared to PT. SPJH showed substantial gains in PTS (P = 0.002), PTW (P = 0.001), and PTSW (P = 0.001) compared to PT. Average jump height and highest jump in ShT were also significantly higher in PTS, PTW, and PTSW (P < 0.05). Additionally, RFDext240°/s was enhanced considerably in PTS (P = 0.001) and PTSW (P = 0.001). Based on the results, plyometric training with speed and weight overloads (PTSW) demonstrated superior enhancements in isokinetic strength, explosive power, and jumping performance. This combined approach is highly effective and significantly benefits male volleyball players, aiming to enhance their physical abilities.

BackgroundMotor unit (MU) activation during maximal contractions is lower in children compared with adults. Among adults, discrete MU activation differs, depending on the rate of contraction. We investigated the effect of contraction rate on discrete MU activation in boys and men.MethodsFollowing a habituation session, 14 boys and 20 men completed two experimental sessions for knee extension and wrist flexion, in random order. Maximal voluntary isometric torque (MVIC) was determined before completing trapezoidal isometric contractions (70%MVIC) at low (10%MVIC/s) and high (35%MVIC/s) contraction rates. Surface electromyography was captured from the vastus lateralis (VL) and flexor carpi radialis (FCR) and decomposed into individual MU action potential (MUAP) trains.ResultsIn both groups and muscles, the initial MU firing rate (MUFR) was greater (p < 0.05) at high compared with low contraction rates. The increase in initial MUFR at the fast contraction in the VL was greater in men than boys (p < 0.05). Mean MUFR was significantly lower during fast contractions only in the FCR (p < 0.05). In both groups and muscles, the rate of decay of MUFR with increasing MUAP amplitude was less steep (p < 0.05) during fast compared with slow contractions.ConclusionIn both groups and muscles, initial MUFRs, as well as MUFRs of large MUs were higher during fast compared with slow contractions. However, in the VL, the increase in initial MUFR was greater in men compared with boys. This suggests that in large muscles, men may rely more on increasing MUFR to generate torque at faster rates compared with boys.

PurposeThe present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters.MethodHealthy men (18–24 years) were placed to either isometric (ISO), concentric (CONC), or eccentric (ECC) group (n = 11/group) that performed corresponding contractions of the knee extensors to exert the same amount of torque-time integral (24,427 ± 291 Nm·s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10 Hz and 100 Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1 h, 1 day and 2 days after each exercise, and were compared among the groups.ResultsMVC torque decreased immediately after ISO (− 17.0 ± 8.3%), CONC (− 21.7 ± 11.5%) and ECC (− 26.2 ± 15.6%) similarly (p = 0.35), but the decrease sustained longer (p < 0.05) for ECC (2 days post-exercise: − 12.9 ± 14.8%) and ISO (− 5.5 ± 7.9%) than CONC (+ 5.0 ± 11.0%). Muscle soreness developed after ECC (25.1 ± 19.8 mm) and ISO (17.5 ± 21.0 mm) similarly (p = 0.15). Voluntary activation decreased immediately (− 3.7 ± 6.6%) and 1 h post-exercise (− 4.7 ± 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (− 30.1 ± 15.6%) and 1 h post-exercise (− 35.0 ± 12.8%) for ECC than others, and the decrease in 10/100 Hz ratio was also greater immediately (− 30.5 ± 12.6%) and 1 h after ECC (− 23.8 ± 10.3%) than others.ConclusionISO, CONC and ECC with the same torque-time integral produced similar neuromuscular fatigue at immediately post-exercise, but the force loss was longer-lasting after ISO and ECC than CONC, and the changes in peripheral fatigue parameters were the greatest after ECC, suggesting greater muscle damage.

PurposeEccentric quasi-isometric (EQI) resistance training is emerging as a promising option in sports medicine and rehabilitation. Despite prior research on EQI contractions in quadriceps and biceps brachii, their use in hamstring injury contexts is underexplored. Therefore, our study examines and contrasts the biomechanics and fatigue effects of EQI training on knee extensors and flexors.MethodsFollowing familiarization, 16 healthy, active participants (9 men, 7 women; 23.5 ± 2.6 years, 72.1 ± 12.8 kg, 173.4 ± 10.7 cm) performed, in random order, four EQI contractions for knee extensions and flexions, respectively. EQI contractions were isotonically loaded to 70% of concentric (60°·s−1) maximal voluntary contraction. Rest between repetitions was set at three minutes, while four minutes separated each muscle group. Peak torque, mean torque, and optimal angle were evaluated pre- and post-bouts. Inter-repetition contraction time and angular velocity were also assessed.ResultsAverage torque was 160.9 ± 44.2 and 71.5 ± 23.2 Nm for the extensors and flexors. Peak and mean torque significantly decreased for both extensors (p < 0.001, d = 0.70–0.71) and flexors (p ≤ 0.022, d = 0.36) after EQI contractions, respectively. However, the optimal angle increased for extensors (p < 0.001, d = 1.00) but not flexors (p = 0.811, d = 0.06). During EQI contractions, knee flexors exhibited greater intra-repetition velocity than extensors (p = 0.002; η2 = 0.50). Decreases in inter-repetition time and range of motion were more consistent for the extensors.ConclusionsDistinct responses exist when comparing EQI contractions of the knee extensors and flexors, particularly their effect on peak torque angles. These findings suggest knee flexors may require lower relative intensities to align more closely with extensor EQI contractions.

BackgroundMaximal conditioning contractions (CCs) can lead to the enhancement of evoked-twitch characteristics in human skeletal muscle. This phenomenon is termed post-activation potentiation (PAP). In the knee extensors, PAP is greater in men compared with boys. In adults, the optimal CC duration for PAP is ~ 10 s. We examined child–adult differences in PAP among females and aimed to determine the optimal CC duration in girls and women.MethodsEleven girls (9.3 ± 1.4 years) and 13 women (23.4 ± 2.7 years) participated in this study. Maximal isometric evoked twitches were recorded in the knee extensors before and after 4 maximal CCs of different durations (5, 10, 20, and 30 s), in a random order. PAP was calculated as the percent-change in peak torque (Tpeak) and peak rate of torque development (RTDpeak) after each CC.ResultsThere was a group-by-duration interaction (p < 0.001), reflecting greater Tpeak PAP in women compared with girls following 5 and 10 s CCs, and lower RTDpeak PAP in women following the 30 s CC. The 5 and 10 s CCs lead to the greatest Tpeak and RTDpeak PAP amongst the women while there were no differences between CC durations in girls.ConclusionAfter both a 5 and 10 s CC, women have greater PAP compared with girls. The optimal CC duration for the knee extensors in women appears to be ~ 5-10 s, while CC durations between 5 and 30 s do not appear to affect levels of PAP in girls.

Purpose This study aimed to evaluate the modulation and reliability of the vastus medialis (VM) and vastus lateralis (VL) H-reflexes in both passive and active conditions. Methods Recruitment curves of VM and VL H-reflexes and M-waves at rest and during muscle contraction (30 % of maximal voluntary contraction) were performed for 12 healthy males and were then repeated after 1 h, 1 day and 1 week. The maximal H-reflexes of each muscle were normalized to their respective maximal M-waves (H/M ratio) and absolute (CV) and relative (ICC) reliability were calculated. Results The H-reflex was potentiated in active compared to passive condition and a higher H-reflex occurrence (12 vs. 10 subjects) and amplitude (≈+150 %) was found for the VM compared to the VL in active condition. The intra- (ICC hour  = 0.97) and inter-day (ICC day  = 0.92; ICC week  = 0.92) reliability was poor for the passive VM H/M ratio due to high within-subject variations (CV hour  = 52.2 %; CV day  = 69.8 %; CV week  = 60.9 %) whereas for the active condition the reliability, especially intra-day, was good (ICC hour  = 0.93 and CV hour  = 12 %; ICC day  = 0.86 and CV day  = 14.5 %; ICC week  = 0.79 and CV week  = 19.7 %). Conclusions This study showed differential modulation of the H-reflex between vasti muscles of the quadriceps and a higher occurrence and reliability for the active VM H-reflex. One can therefore conclude that it seems more appropriate to evoke quadriceps VM H-reflex (rather than VL) during an isometric muscle contraction.

(1) Background: Childhood obesity is an important public health problem. Children with overweight or obesity often tend to show the pediatric inactivity triad components; these involve exercise deficit disorder, pediatric dynapenia, and physical illiteracy. The aim of the study was to examine the influence of an active video games (AVG) intervention combined with multicomponent exercise on muscular fitness, physical activity (PA), and motor skills in children with overweight or obesity. (2) Methods: A total of 29 (13 girls) children (10.07 ± 0.84 years) with overweight or obesity were randomly allocated in the intervention group (AVG group; n = 21) or in the control group (CG; n = 8). The intervention group performed a 5-month AVG training using the Xbox 360® with the Kinect, the Nintendo Wii®, dance mats, and the BKOOL® interactive cycling simulator, combined with multicomponent exercise, performing three sessions per week. The control group continued their daily activities without modification. Weight, PA using accelerometers, and motor competence using the Test of Gross Motor Development 3rd edition were measured. Muscular fitness was evaluated through the Counter Movement Jump height, maximal isometric strength of knee extension and handgrip strength, and lean mass using Dual-energy X-ray Absorptiometry. Mann–Whitney U and Wilcoxon signed rank tests were performed. The biserial correlation coefficients (r) were calculated. Spearman’s correlation coefficients among PA, muscular fitness, and motor competence variables were also calculated. (3) Results: The AVG group significantly increased their knee extension maximal isometric strength (4.22 kg; p < 0.01), handgrip strength (1.93 kg; p < 0.01), and jump height (1.60 cm; p < 0.01), while the control group only increased the knee extension maximal isometric strength (3.15 kg; p < 0.01). The AVG group improved motor competence and light physical activity (p < 0.05) and decreased sedentary time (p < 0.05). Lean mass improved in both AVG group and CG (p < 0.05). Lastly, the percentage of improvement of motor skills positively correlated with the percentage of improvement in vigorous PA (r = 0.673; p = 0.003) and the percentage of improvement in CMJ (r = 0.466; p = 0.039). (4) Conclusions: A 5-month intervention combining AVG with multicomponent training seems to have positive effects on muscle fitness, motor competence, and PA in children with overweight or obesity.