Delayed neuromuscular fatigue recovery unveils reduced fatigue tolerance in elderly following maximal intermittent exercise.

The aim of the study was to assess the impact of aging on neuromuscular fatigue and recovery. Ten young (23.08 ± 1.43 years) and older (61.19 ± 1.80 years) males performed an intermittent maximal isometric exercise with the knee extensors followed by 27 min of recovery. Maximal voluntary contraction (MVC), total work (W'), voluntary activation (VA), potentiated resting twitch (Ptw), and electromyography (EMG) were recorded and then analyzed. Peripheral and central fatigue following exercise were lower in old compared to young (- 29.99% vs. - 42.68% and - 14.55 vs. - 20.02%; P < 0.05, respectively). Despite old performing 50% less work, RMS/Mmax reduction was similar between old and young (- 26.46% vs. - 29.93%; P > 0.05, respectively). During the recovery period, our results showed that recovery of the MVC was impaired for old (14.93% for old vs. 30.66% for young) and still incomplete until 27 min.VA increased significantly compared to post exercise after 1 min only for young (P = 0.001), potentially affecting the recovery pattern of MVC during the early phase due to their significant correlation (r2 = 0.58, P = 0.01). Peripheral fatigue recovery was also lower for old (11.18% vs. 18.72%; P < 0.001), and both groups failed to recover their baseline value (both P < 0.005). The lower peripheral and central fatigue observed in elderly following exercise appears for the first instance as a fatigue resistance. However, the delayed neuromuscular recovery reveals instead a reduced fatigue tolerance reflecting age-related alteration within contractile properties and/or within central nervous system.

Hemodynamic and neuromuscular basis of reduced exercise capacity in patients with end-stage renal disease.

PURPOSE: The present study aimed to characterize the exercise-induced neuromuscular fatigue and its possible links with cerebral and muscular oxygen supply and utilization to provide mechanistic insights into the reduced exercise capacity characterizing patients with end-stage renal disease (ESRD). METHODS: Thirteen patients with ESRD and thirteen healthy males (CTR group) performed a constant-force sustained isometric contraction at 50% of their maximal voluntary isometric contraction (MVC) until exhaustion. Quadriceps muscle activation during exercise was estimated from vastus lateralis, vastus medialis, and rectus femoris EMG. Central and peripheral fatigue were quantified via changes in pre- to postexercise quadriceps voluntary activation (ΔVA) and quadriceps twitch force (ΔQtw,pot) evoked by supramaximal electrical stimulation, respectively. To assess cerebral and muscular oxygenation, throughout exercise, near-infrared spectroscopy allowed investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the prefrontal cortex and in the vastus lateralis muscle. RESULTS: ESRD patients demonstrated lower exercise time to exhaustion than that of CTR (88.8 ± 15.3 s and 119.9 ± 14.6 s, respectively, P < 0.01). Following the exercise, MVC, Qtw,pot, and VA reduction were similar between the groups (P > 0.05). There was no significant difference in muscle oxygenation (∆O2Hb) between the two groups (P > 0.05). Cerebral and muscular blood volume (∆THb) and oxygen extraction (∆HHb) were significantly blunted in the ESRD group (P < 0.05). A significant positive correlation was observed between time to exhaustion and cerebral blood volume (∆THb) in both groups (r2 = 0.64, P < 0.01). CONCLUSIONS: These findings support cerebral hypoperfusion as a factor contributing to the reduction in exercise capacity characterizing ESRD patients.

The impact of a 40-min nap on neuromuscular fatigue profile and recovery following the 5-m shuttle run test.

This study aims to investigate the impact of a 40-min nap opportunity on perceived recovery, exertion, and maximal voluntary isometric contraction (MVIC) following the 5-m shuttle run test (5SRT), after 1 night of normal sleep. In a randomised, counterbalanced, cross-over design, 17 trained men (mean [SD] age 20 [3] years, height 173 [6] cm, body mass 68 [6] kg) performed a 5SRT under two conditions: a 40-min nap opportunity and no-nap condition. After both conditions, electromyography signals during a 5-s isometric knee extension were recorded before and immediately after the 5SRT. Two electrical nerve stimulations at the femoral nerve were measured during and after the MVIC. Force, voluntary activation level, M-wave amplitudes, potentiated twitch, and electromyography signals (root mean square) were measured during each MVIC. Perceived exertion was recorded after each repetition of the test and perceived recovery was determined after the end of the MVIC. Compared to the no-nap condition, the 40-min nap resulted in significant enhancements in both the highest distance (p < 0.01, Δ = +7.6%) and total distance (p < 0.01, Δ = +7.5%). Before and after exercise, values for MVIC, root mean square, M-wave amplitudes, and voluntary activation level were improved after the 40-min nap opportunity compared to no-nap condition (all p ≤ 0.01). Values for perceived exertion and recovery were improved after the 40-min nap opportunity in comparison with no-nap condition (p ≤ 0.01). A 40-min nap opportunity improved repeated high-intensity short-term maximal performance, perceived recovery, associated neuromuscular responses, and reduced perceived fatigue. Therefore, our findings suggest that central and peripheral processes are involved in the improvements of 5SRT performance after napping.

Chronic beetroot juice supplementation attenuates neuromuscular fatigue etiology during simulated soccer match play.

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 Qtw,pot) and central fatigue (voluntary activation, VA). Compared with baseline, MVC Qtw,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 Qtw,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.

Peripheral fatigue regulation during knee extensor exercise in type 1 diabetes and consequences on the force-duration relationship.

PURPOSE: This study aimed to examine if peripheral fatigue is adjusted during knee extensor (KE) exercise in order not to surpass a critical threshold patient with type 1 diabetes (T1D) and the consequences of this mechanism on the force-duration relationship. METHODS: Eleven T1D individuals randomly performed two different sessions in which they performed 60 maximum voluntary contractions (MVC; 3 s contraction, 2 s relaxation). One trial was performed in the non-fatigued state (CTRL) and another after fatiguing neuromuscular stimulation of the KE (FNMES). Peripheral and central fatigue were quantified by the difference between pre and post exercise in quadriceps voluntary activation (ΔVA) and potentiated twitch (ΔPtw). Critical torque (CT) was determined as the average force of the last 12 contractions, whereas W' was calculated as the area above the CT. RESULTS: Although FNMES led to a significant decrease in potentiated twitch (Ptw) before performing the 60-MVCs protocol (p < 0.05), ΔVA (∼ -7.5%), ΔPtw (∼ -39%), and CT (∼816 N) post-MVCs were similar between the two conditions. The difference in W' between CTRL and FNMES was correlated with the level of pre-fatigue induced in FNMES (r2 = 0.60). In addition, W' was correlated with ΔPtw (r2 = 0.62) in the CTRL session. CONCLUSION: Correlative results in the present study indicate that regulating peripheral fatigue mechanisms at a critical threshold limit W'. Additionally, peripheral fatigue during KE exercise is limited to an individual threshold in T1D patients.

Jump and sprint force velocity profile of young soccer players differ according to playing position.

Our study aimed to compare explosive performance and underlying mechanical determinants explored through F-V profiles in jumping and sprinting among young soccer players based on their playing position. Ninety elite soccer players were categorized into the following positions: goalkeepers, central defenders, wide defenders, central midfielders, wide midfielders, and forwards. Two testing sessions were conducted to measure the 30-metre sprint time (T30) using an over-ground sprint test and jump height (Hmax) through the SJ test. Results demonstrated performance variations among positions. In sprinting, forwards showed greater T30 (4.5 ± 0.14 s) compared to other positions, with goalkeepers exhibiting the lowest T30 (4.86 ± 0.18 s). Forwards also displayed higher maximal theoretical velocity (8.8 ± 0.4 m.s-1) and power output (Pmax) (19.4 ± 2.6 W.kg-1) than other positions, while goalkeepers had the lowest Pmax (16.5 ± 2 W.kg-1). In jumping, forwards (33.2 ± 3.9 cm) and wide-midfielders (33.6 ± 3.8 cm) achieved higher Hmax compared to goalkeepers (29.2 ± 5 cm) and central-midfielders (29.2 ± 3.8 cm). Wide-midfielders (28.5 ± 4.8 W.kg-1) and forwards (27.1 ± 4.3 W.kg-1) surpassed goalkeepers (23 ± 2.8 W.kg-1) and central-midfielders (25.1 ± 3.8 W.kg-1) in Pmax. Our findings reveal substantial position-related disparities in F-V profiles among elite young soccer players, in sprinting and jumping emphasizing the need for position-specific training programmes to optimize player development and on-field performance from an early age.

Cold Water Immersion Improves the Recovery of Both Central and Peripheral Fatigue Following Simulated Soccer Match-Play.

The present study aimed to investigate the effect of cold water immersion (CWI) on the recovery of neuromuscular fatigue following simulated soccer match-play. In a randomized design, twelve soccer players completed a 90-min simulated soccer match followed by either CWI or thermoneutral water immersion (TWI, sham condition). Before and after match (immediately after CWI/TWI through 72 h recovery), neuromuscular and performance assessments were performed. Maximal voluntary contraction (MVC) and twitch responses, delivered through electrical femoral nerve stimulation, were used to assess peripheral fatigue (quadriceps resting twitch force, Qtw,pot) and central fatigue (voluntary activation, VA). Performance was assessed via squat jump (SJ), countermovement jump (CMJ), and 20 m sprint tests. Biomarkers of muscle damages (creatine kinase, CK; Lactate dehydrogenase, LDH) were also collected. Smaller reductions in CWI than TWI were found in MVC (-9.9 ± 3%vs-23.7 ± 14.7%), VA (-3.7 ± 4.9%vs-15.4 ± 5.6%) and Qtw,pot (-15.7 ± 5.9% vs. -24.8 ± 9.5%) following post-match intervention (p < 0.05). On the other hand, smaller reductions in CWI than TWI were found only in Qtw,pot (-0.2 ± 7.7% vs. -8.8 ± 9.6%) at 72 h post-match. Afterwards, these parameters remained lower compared to baseline up to 48-72 h in TWI while they all recovered within 24 h in CWI. The 20 m sprint performance was less impaired in CWI than TWI (+11.1 ± 3.2% vs. +18 ± 3.6%, p < 0.05) while SJ and CMJ were not affected by the recovery strategy. Plasma LDH, yet no CK, were less increased during recovery in CWI compared to TWI. This study showed that CWI reduced both central and peripheral components of fatigue, which in turn led to earlier full recovery of the neuromuscular function and performance indices. Therefore, CWI might be an interesting recovery strategy for soccer players.

Immediate voluntary activation deficits following submaximal eccentric contractions of knee extensors are associated with alterations of the sense of movement.

The mechanisms underlying movement sense alterations following repeated eccentric contractions remain unclear. This study concomitantly investigated the effects of unilateral eccentric contractions on movement sense and on neuromuscular function at the knee before, immediately after (POST), 24 (POST24) and 48 (POST48) h after the exercise. Twelve participants performed sets of submaximal knee extensors (KE) eccentric contractions until a 20% decrease in maximal voluntary isometric contraction (MVIC) torque was reached. Threshold to detect passive movement (TTDPM) tasks were used to assess movement sense during both knee flexion (TTDPMFLEX) and extension (TTDPMEXT). KE fatigability was assessed using the interpolated twitch technique. TTDPM values expressed in seconds and the percentage of unsuccessful trials only increased at POST during TTDPMFLEX and TTDPMEXT. The 20%-MVIC decrease was associated with significant decreases in voluntary activation level (- 12.7%, p < 0.01) and potentiated doublet torque at 100 Hz (- 18.1%, p < 0.001). At POST24, despite persistent reductions of maximal voluntary and electrically evoked torques associated with increased perceived muscle soreness, TTDPM values and the percentage of unsuccessful trials returned to baseline values. Consequently, movement sense alterations were only observed in the presence of voluntary activation deficits, suggesting that some exercise-induced central alterations may affect the somatosensory function.

Neuromuscular Fatigue in Individuals With Intellectual Disability: Comparison Between Sedentary Individuals and Athletes.

The authors explored neuromuscular fatigue in athletes with intellectual disability (AID) compared with sedentary individuals with intellectual disability (SID) and individuals with typical development. Force, voluntary activation level, potentiated resting twitch, and electromyography signals were assessed during isometric maximal voluntary contractions performed before and immediately after an isometric submaximal exhaustive contraction (15% isometric maximal voluntary contractions) and during recovery period. AID presented shorter time to task failure than SID (p < .05). The three groups presented similar isometric maximal voluntary contraction decline and recovery kinetic. Both groups with intellectual disability presented higher voluntary activation level and root mean square normalized to peak-to-peak M-wave amplitude declines (p < .05) compared with individuals with typical development. These declines were more pronounced in SID (p < .05) than in AID. The AID recovered their initial voluntary activation level later than controls, whereas SID did not. SID presented lower potentiated resting twitch decline compared with AID and controls with faster recovery (p < .05). AID presented attenuated central fatigue and accentuated peripheral fatigue compared with their sedentary counterparts, suggesting a neuromuscular profile close to that of individuals with typical development.

Altered Position Sense after Submaximal Eccentric Exercise-inducing Central Fatigue.

PURPOSE: The purpose of this study was to concomitantly investigate the acute and delayed effects of a submaximal eccentric-induced muscle fatigue on the position sense and the neuromuscular function of the right knee extensor muscles. METHODS: Thirteen young and physically active participants performed a unilateral isokinetic eccentric exercise of their right lower limb until a decrease in maximal voluntary isometric contraction (MVIC) of 20% was reached. Neuromuscular (i.e., MVIC, voluntary activation (VA) level, and evoked contractile properties [DB100 and DB10]) and psychophysical evaluations (i.e., bilateral position-matching task, perceived muscle soreness, and perceived fatigue) were performed at four time points: before (PRE), immediately after (POST), 24 (POST24), and 48 (POST48) the exercise. RESULTS: The acute 20% MVIC reduction (P < 0.001) was associated with both central (i.e., -13% VA decrease, P < 0.01) and peripheral (i.e., -18% and -42% reduction of DB100 and DB10, respectively, P < 0.001) fatigue. In the following days (POST24 and POST48), VA levels had recovered despite the presence of a persisting peripheral fatigue and delayed-onset muscle soreness. Knee position sense, as revealed by position errors, was significantly altered only at POST (P < 0.05) with participants overestimating the length of their knee extensor. Position errors and VA deficits were significantly correlated at POST (r = -0.60, P = 0.03). Position errors returned to nonsignificant control values in the following days. CONCLUSION: The acute central fatigue induced by the eccentric exercise contributes to the position sense disturbances. Central fatigue might lead to alterations in the sensory structures responsible for the integration and the processing of position-related sensory inputs.

Aging reduces the maximal level of peripheral fatigue tolerable and impairs exercise capacity.

The aim of the present study was to determine the magnitude of the maximal level of peripheral fatigue attainable (fatigue threshold) during an all-out intermittent isometric knee-extensor protocol in both younger (24 ± 1 yr, n = 12) and older (60 ± 2 yr, n = 12) participants to provide new insights into the effects of aging on neuromuscular function. Participants performed two experimental sessions, in which they performed 60 maximal voluntary contractions (MVCs; 3 s of contraction, 2 s of relaxation). One trial was performed in the unfatigued state (CTRL) and one other following fatiguing neuromuscular electrical stimulation of the quadriceps (FNMES). Peripheral fatigue was quantified via pre/postexercise decrease in quadriceps twitch force (∆Ptw). Critical force (CF) was determined as the mean force output of the last 12 contractions, whereas W' was calculated as the area above CF. Although FNMES led to a significant decrease in Ptw before performing the 60-MVCs protocol (P = 0.024), ∆Ptw was not different between CTRL and FNMES for both the young group (P = 0.491) and the old group (P = 0.523). However, this peripheral fatigue threshold was significantly greater in young versus old participants (∆Ptw = -48 ± 10% vs. -29 ± 13%, respectively, P = 0.028). In CTRL, W' was 55 ± 13% lower in the old group than in the young group (P < 0.001), but CF was similar (326 ± 10 N vs. 322 ± 12 N, respectively, P = 0.941). ∆Ptw was correlated with W', independently of age (r2 = 0.84, P < 0.001). Exercise performance decreases with aging consequent to a lower tolerance to peripheral fatigue. However, the peripheral fatigue threshold mechanism persists with healthy aging and continues to play a protective role in preserving locomotor muscle function during exercise.

Centrally-mediated regulation of peripheral fatigue during knee extensor exercise and consequences on the force-duration relationship in older men.

The aim of the present study was to investigate the existence of a critical threshold beyond which peripheral fatigue would not further decrease during knee extensor (KE) exercise in older men, and the consequences of this mechanism on the force-duration relationship. Twelve old men (59 ± 2 years) randomly performed two different sessions, in which they performed 60 maximum voluntary contractions (MVC; 3s contraction, 2s relaxation). One trial was performed in the unfatigued state (CTRL) and one other following fatiguing neuromuscular electrical stimulation of the KE (FNMES). Peripheral and central fatigue were quantified via pre/post-exercise decreases in quadriceps twitch-force (Δ Ptw) and voluntary activation (ΔVA). Critical torque (CT) was determined as the mean force of the last 12 contractions while W' was calculated as the area above CT. Compared with CTRL, pre-fatigue (Δ Ptw = -10.3 ± 6.2%) resulted in a significant (p < 0.05) reduction in W' (-18.2 ± 1.6%) in FNMES. However, CT (∼964 N), ΔVA (∼15%) and Δ Ptw (∼25%) post-MVCs were similar between both conditions. In CTRL, W' was correlated with Δ Ptw (r 2 = 0.78). Moreover, the difference in W' between CTRL and FNMES was correlated with the level of pre-fatigue induced in FNMES (r 2 = 0.76). These findings document that peripheral fatigue is confined to an individual threshold during KE exercise in older men. Furthermore, correlative results suggest that mechanisms regulating peripheral fatigue to a critical threshold also restrict W', and therefore play a role in exercise capacity in older men.

Effect of the Anode Placement on the Antagonist Muscles Recruitment: Implication for the Interpolated Twitch Technique Outcome.

The aim of the present study was to compare the recruitment of the antagonist muscles and its effect on the measurement of the voluntary activation level (VA) of the knee extensor (KE) muscles for different anode placements used to stimulate the femoral nerve. We hypothesized that when the anode is positioned over the gluteal fold (GF), the antagonist muscles recruitment would be greater and, thus the VA overestimated, than when the anode is placed midway between the greater trochanter and the lower border of the iliac crest (Midtroc-iliac). Thirteen healthy men (23 ± 4 yr) were tested in both conditions (GF vs. Midtroc-iliac) in a randomized order. Recruitment curves were performed to determine the optimal stimulus intensity (Iopt) and quantify antagonist muscles recruitment (i.e. biceps femoris M-wave). Participants performed maximal voluntary isometric contractions (MVIC) and the interpolated twitch technique was used to measured VA. Antagonist muscles recruitment was greater when the anode was placed over the GF than Midtroc-iliac. The Iopt was also lower for GF than Midtroc-iliac placement. However, no significant effect of anode placement was found for the interpolated twitch technique outcome. When the anode was placed over the GF, antagonist muscles recruitment was greater, inducing optimal stimulus intensity underestimation. However, it did not affect VA assessment. To fully avoid this potential limitation, Midtroc-iliac anode placement should nevertheless be preferred for the KE neuromuscular function assessment, owing to the reduced recruitment of the antagonist muscles.

Combined Resistance and Plyometric Training Is More Effective Than Plyometric Training Alone for Improving Physical Fitness of Pubertal Soccer Players.

The purpose of this study was to compare the effects of combined resistance and plyometric/sprint training with plyometric/sprint training or typical soccer training alone on muscle strength and power, speed, change-of-direction ability in young soccer players. Thirty-one young (14.5 ± 0.52 years; tanner stage 3-4) soccer players were randomly assigned to either a combined- (COMB, n = 14), plyometric-training (PLYO, n = 9) or an active control group (CONT, n = 8). Two training sessions were added to the regular soccer training consisting of one session of light-load high-velocity resistance exercises combined with one session of plyometric/sprint training (COMB), two sessions of plyometric/sprint training (PLYO) or two soccer training sessions (CONT). Training volume was similar between the experimental groups. Before and after 7-weeks of training, peak torque, as well as absolute and relative (normalized to torque; RTD r ) rate of torque development (RTD) during maximal voluntary isometric contraction of the knee extensors (KE) were monitored at time intervals from the onset of contraction to 200 ms. Jump height, sprinting speed at 5, 10, 20-m and change-of-direction ability performances were also assessed. There were no significant between-group baseline differences. Both COMB and PLYO significantly increased their jump height (Δ14.3%; ES = 0.94; Δ12.1%; ES = 0.54, respectively) and RTD at mid to late phases but with greater within effect sizes in COMB in comparison with PLYO. However, significant increases in peak torque (Δ16.9%; p < 0.001; ES = 0.58), RTD (Δ44.3%; ES = 0.71), RTD r (Δ27.3%; ES = 0.62) and sprint performance at 5-m (Δ-4.7%; p < 0.001; ES = 0.73) were found in COMB without any significant pre-to-post change in PLYO and CONT groups. Our results suggest that COMB is more effective than PLYO or CONT for enhancing strength, sprint and jump performances.

Neuromuscular fatigue and recovery profiles in individuals with intellectual disability.

PURPOSE: This study aimed to explore neuromuscular fatigue and recovery profiles in individuals with intellectual disability (ID) after exhausting submaximal contraction. METHODS: Ten men with ID were compared to 10 men without ID. The evaluation of neuromuscular function consisted in brief (3 s) isometric maximal voluntary contraction (IMVC) of the knee extension superimposed with electrical nerve stimulation before, immediately after, and during 33 min after an exhausting submaximal isometric task at 15% of the IMVC. Force, voluntary activation level (VAL), potentiated twitch (Ptw), and electromyography (EMG) signals were measured during IMVC and then analyzed. RESULTS: Individuals with ID developed lower baseline IMVC, VAL, Ptw, and RMS/Mmax ratio (root-mean-square value normalized to the maximal peak-to-peak amplitude of the M-wave) than controls (p < 0.05). Nevertheless, the time to task failure was significantly longer in ID vs. controls (p < 0.05). The 2 groups presented similar IMVC decline and recovery kinetics after the fatiguing exercise. However, individuals with ID presented higher VAL and RMS/Mmax ratio declines but lower Ptw decline compared to those without ID. Moreover, individuals with ID demonstrated a persistent central fatigue but faster recovery from peripheral fatigue. CONCLUSION: These differences in neuromuscular fatigue profiles and recovery kinetics should be acknowledged when prescribing training programs for individuals with ID.

The effects of Ramadan intermittent fasting on the underlying mechanisms of force production capacity during maximal isometric voluntary contraction.

The aim of the present study was to investigate the effects of Ramadan intermittent fasting (RIF) on the underlying mechanisms of force production capacity during maximal voluntary isometric contraction (MVIC) using the superimposed twitch technique. Ten healthy male physical education students performed three MVIC of the knee extensor superimposed with nerve electrical stimulation during four testing phases: one week before Ramadan (BR), at the end of the first week of Ramadan (R-1), during the fourth week of Ramadan (R-4) and two weeks after Ramadan (AR). This study was performed during Ramadan 2016. MVIC values, voluntary activation level (VAL), potentiated resting twitch and electromyography signals were recorded during each MVIC. The French version of the Profile of Mood States questionnaire (POMS-f) was used to evaluate the subjective mood states in each testing session. The results showed that MVIC values (890.57 ± 67.90 vs. 816.46 ± 54.72 N) and VAL (87.73 ± 3.27 vs. 77.32 ± 7.87%) decreased at R-1 compared to BR (p < 0.001). However, the neuromuscular efficiency and the potentiated resting twitch remained unchanged during Ramadan (R). Results showed that depression (p < 0.01; 6.3 ± 1.57 vs. 4.7 ± 1.25), fatigue (p < 0.001; 9.2 ± 1.93 vs. 4.6 ± 2.01) and anxiety (p < 0.001; 6.4 ± 1.51 vs. 11.8 ± 1.23) scores of POMS-f were higher during R-1 compared to BR. In conclusion, RIF-related impairment of maximal muscle force seems to be related to nervous alterations of the VAL, whereas the RIF did not adversely affect peripheral mechanisms. Abbreviations' List: ANOVA: Analysis of variance; AR: After Ramadan; BMI: Body-mass index; BR: Before Ramadan; EMG: Electromyography; ER: End of Ramadan; MF: Mean frequency; Mmax: Peak-to-peak M-wave amplitudes; MVIV: Maximal voluntary isometric contraction; NES: Nerve electrical stimulation; NME: Neuromuscular efficiency; POMS-f: French version of the Profile of Mood States questionnaire; R: Ramadan; R-1: First week of Ramadan; R-4: Fourth week of Ramadan; RF: Rectus femoris; RIF: Ramadan intermittent fasting; RMS: Root mean square; VAL: Voluntary activation level; VL: Vastus lateralis; VM: Vastus medialis.

Individuals with intellectual disability have lower voluntary muscle activation level.

The aim of this study was to explore the voluntary activation level during maximal voluntary contraction (MVC) in individuals with intellectual disability (ID) versus individuals without ID using the twitch interpolation technique. Ten individuals with mild ID (ID group) and 10 sedentary men without ID (control group) participated in this study. The evaluation of neuromuscular function consisted in three brief MVCs (3s) of the knee extension superimposed with electrical nerve stimulation (NES) to measure voluntary activation. Muscle activity levels were also measured with surface EMG. The root mean square (RMS) was extracted from the EMG signal. The RMS/Mmax ratio and the neuromuscular efficiency (NME) were calculated. Our results reported that individuals with ID present lower muscle strength (p < 0.001), lower voluntary activation level (p < 0.001), lower RMS values of vastus lateralis (p < 0.05), vastus medialis (p < 0.05), and rectus femoris (p < 0.001) muscles. In addition, our results showed lower RMS/Mmax values in the ID group than in the control group for the VM (0.05 ± 0.01 mV vs. 0.04 ± 0.01 mV; p < 0.05) and the RF (0.06 ± 0.02 mV vs. 0.05 ± 0.02 mV; p < 0.05) muscles. However, no significant difference was reported for the VL muscle (0.05 ± 0.02 mV vs. 0.05 ± 0.02 mV; p=0.463). Moreover, Individuals with ID present smaller potentiated twitch (p < 0.001). However, no significant difference was reported in the NME ratio. These results suggest that the lower muscle strength known in individuals with ID is related to a central nervous system failure to activate motor units and to some abnormal intrinsic muscle properties. It seems that the inactive lifestyle adopted by individuals with ID is one of the most important factors of their lower voluntary activation levels. Therefore, physical activities should be introduced in life style of individuals with ID to improve their neuromuscular function.

Neuromuscular fatigue during high-intensity intermittent exercise in individuals with intellectual disability.

This study examined neuromuscular fatigue after high-intensity intermittent exercise in 10 men with mild intellectual disability (ID) in comparison with 10 controls. Both groups performed three maximal voluntary contractions (MVC) of knee extension with 5 min in-between. The highest level achieved was selected as reference MVC. The fatiguing exercise consists of five sets with a maximal number of flexion-extension cycles at 80% of the one maximal repetition (1RM) for the right leg at 90° with 90 s rest interval between sets. The MVC was tested again after the last set. Peak force and electromyography (EMG) signals were measured during the MVC tests. Root Mean Square (RMS) and Median Frequency (MF) were calculated. Neuromuscular efficiency (NME) was calculated as the ratio of peak force to the RMS. Before exercise, individuals with ID had a lower MVC (p<0.05) and a lower RMS (p<0.05). No significant difference between groups in MF and NME. After exercise, MVC decreases significantly in both groups (p<0.001). Individuals with ID have greater force decline (p<0.001 vs. p<0.01). RMS decreased significantly (p<0.001) whereas the NME increased significantly (p<0.05) in individuals with ID, but both remained unchanged in controls. The MF decreased significantly in both groups (p<0.001). In conclusion, individuals with ID presented a lower peak force than individuals without ID. After a high-intensity intermittent exercise, individuals with ID demonstrated a greater force decline caused by neural activation failure. When rehabilitation and sport train ID individuals, they should consider this nervous system weakness.