Does Grappling Combat Sports Experience Influence Exercise Tolerance of Handgrip Muscles in the Severe-Intensity Domain?

Successful performance in grappling combat sports (GCS) can be influenced by the fighter's capacity to sustain high-intensity contractions of the handgrip muscles during combat. This study investigated the influence of GCS experience on the critical torque (CT), impulse above CT (W'), tolerance, and neuromuscular fatigue development during severe-intensity handgrip exercise by comparing fighters and untrained individuals. Eleven GCS fighters and twelve untrained individuals participated in three experimental sessions for handgrip muscles: (1) familiarization with the experimental procedures and strength assessment; (2) an all-out test to determine CT and W'; and (3) intermittent exercise performed in the severe-intensity domain (CT + 15%) until task failure. No significant differences were found in CT and neuromuscular fatigue between groups (p > 0.05). However, GCS fighters showed greater W' (GCS fighters 2238.8 ± 581.2 N·m·s vs. untrained 1670.4 ± 680.6 N·m·s, p < 0.05) and exercise tolerance (GCS fighters 8.38 ± 2.93 min vs. untrained 5.36 ± 1.42 min, p < 0.05) than untrained individuals. These results suggest that long-term GCS sports training can promote increased tolerance to severe-intensity handgrip exercise and improved W' without changes in CT or the magnitude of neuromuscular fatigue.

Effects of caffeine on central and peripheral fatigue following closed- and open-loop cycling exercises

We examined whether endurance performance and neuromuscular fatigue would be affected by caffeine ingestion during closed- and open-loop exercises. Nine cyclists performed a closed-loop (4,000-m cycling time trial) and an open-loop exercise (work rate fixed at mean power of the closed-loop trial) 60 min after ingesting caffeine (CAF, 5 mg/kg) or placebo (PLA, cellulose). Central and peripheral fatigue was quantified via pre- to post-exercise decrease in quadriceps voluntary activation and potentiated twitch force, respectively. Test sensitivity for detecting caffeine-induced improvements in exercise performance was calculated as the mean change in time divided by the error of measurement. Caffeine ingestion reduced the time of the closed-loop trial (PLA: 375.1±14.5 s vs CAF: 368.2±14.9 s, P=0.024) and increased exercise tolerance during the open-loop trial (PLA: 418.2±99.5 s vs CAF: 552.5±106.5 s, P=0.001), with similar calculated sensitivity indices (1.5, 90%CI: 0.7-2.9 vs 2.8, 90%CI: 1.9-5.1). The reduction in voluntary activation was more pronounced (P=0.019) in open- (-6.8±8.3%) than in closed-loop exercises (-1.9±4.4%), but there was no difference between open- and closed-loop exercises for the potentiated twitch force reduction (-25.6±12.8 vs -26.6±12.0%, P>0.05). Caffeine had no effect on central and peripheral fatigue development in either mode of exercise. In conclusion, caffeine improved endurance performance in both modes of exercise without influence on post-exercise central and peripheral fatigue, with the open-loop exercise imposing a greater challenge to central fatigue tolerance.

A New Approach to Evaluate Neuromuscular Fatigue of Extensor Elbow Muscles.

Neuromuscular fatigue evaluation is widely performed on different muscles through the conventional protocol using maximum voluntary contraction (MVC) with electrical stimuli in the analyzed muscle. In an attempt to use this protocol on elbow extensor musculature, previous studies and pilot studies showed co-contraction effects from antagonist musculature during muscular stimulations. The aim of this study was to propose a new neuromuscular fatigue protocol evaluation on elbow extensor musculature. Twenty participants preformed exercises to induce central (CenFat) and peripheral fatigue (PerFat). Neuromuscular fatigue was evaluated on knee extensor muscles by a conventional protocol that provides Twitch Superimposed (TSK) and Twitch Potentiated (TPK), central and peripheral parameters respectively. For elbow extensor muscles, the protocol used sustained submaximal contraction at 10, 20, 30, 40, and 50% of MVC. The neuromuscular fatigue in upper limbs was identified by Twitch Potentiated (TPE) and multiple Twitch Superimposed (TSE) parameters. Using the relationship between MVC (%) and evoked force, the proposed protocol used several TSE to provide slope, y-intercept and R 2. It is proposed that slope, R 2, and y-intercept change may indicate peripheral fatigue and the identified relationship between y-intercept and R 2 may indicate central fatigue or both peripheral and central fatigue. The results were compared using the non-parametric analyzes of Friedmann and Wilcoxon and their possible correlations were verified by the Spearmann test (significance level set at p < 0.05). After PerFat a decrease in TPE (57.1%, p < 0.001) was found but not in any TSE, indicating only peripheral fatigue in upper limbs. After CenFat a decrease in TPE (21.4%, p: 0.008) and TPK (20.9%, p < 0.001) were found but not in TSK, indicating peripheral fatigue in upper and lower limbs but not central fatigue. A non-significant increase of 15.3% after CenFat and a statistical reduction (80.1%, p: 0.001) after PerFat were found by slope. Despite R 2 showing differences after both exercises (p < 0.05), it showed a recovery behavior after CenFat (p: 0.016). Although PerFat provided only peripheral fatigue, CenFat did not provide central fatigue. Considering the procedural limitations of CenFat, parameters resulting from the proposed protocol are sensitive to neuromuscular alteration, however, further studies are required.

Comparison of High-Volume and High-Intensity Upper Body Resistance Training on Acute Neuromuscular Performance and Ratings of Perceived Exertion.

The assessment of neuromuscular fatigue is important for minimizing the risks of nonfunctional overreaching, and monitoring training loads has rapidly grown in recent years. The objective of the study was to compare the acute upper body performance and rating of perceived exertion (RPE) responses to high-volume (HV) and high-intensity (HI) resistance-training loads. Sixteen young resistance-trained men (4 repetition maximum [RM] bench press = 105.8 ± 15.9 kg) were divided into two groups of eight subjects each that performed a HI (3 sets of 4RM with 180 s of rest), and a HV (4 sets of 12RM with 90 s of rest) training sessions. Session RPE was obtained 30 min Post. The medicine-ball throw (MBT) performance was measured at pre, and 10 min post. Training volume load (movements × load), and intensity (volume load ÷ movements) were calculated. Volume load was significantly higher for HV (10890 ± 1241 kg) than HI (2718 ± 413 kg) protocol (p < 0.001). Intensity was significantly higher for HI (100.7 ± 15.3 kg) than HV (75.6 ± 8.6 kg) protocol (p = 0.002). MBT performance was significantly reduced from pre- to post- HV (p < 0.001; Δ = -11%), but not in HI (p = 0.15; Δ = -5%). RPE was significantly higher Post-HI (9.9 ± 0.4) than Post HV (8.9 ± 0.8) (p = 0.01). We conclude that higher volume loads induce greater upper body neuromuscular fatigue in young resistance-trained men. Session RPE may reflect training intensity, but not the performance impairments.

Caffeine increases peripheral fatigue in low- but not in high-performing cyclists.

The influence of cyclists' performance levels on caffeine-induced increases in neuromuscular fatigue after a 4-km cycling time trial (TT) was investigated. Nineteen cyclists performed a 4-km cycling TT 1 h after ingesting caffeine (5 mg·kg-1) or placebo (cellulose). Changes from baseline to after exercise in voluntary activation (VA) and potentiated 1 Hz force twitch (Qtw,pot) were used as markers of central and peripheral fatigue, respectively. Participants were classified as "high performing" (HP, n = 8) or "low performing" (LP, n = 8) in accordance with their performance in a placebo trial. Compared with placebo, caffeine increased the power, anaerobic mechanical power, and anaerobic work, reducing the time to complete the trial in both groups (p < 0.05). There was a group versus supplement and a group versus supplement versus trial interaction for Qtw,pot, in which the postexercise reduction was greater after caffeine compared with placebo in the LP group (Qtw,pot = -34% ± 17% vs. -21% ± 11%, p = 0.02) but not in the HP group (Qtw,pot = -22% ± 8% vs. -23% ± 10%, p = 0.64). There was no effect of caffeine on VA, but there was a group versus trial interaction with lower postexercise values in the LP group than in the HP group (p = 0.03). Caffeine-induced improvement in 4-km cycling TT performance seems to come at the expense of greater locomotor muscle fatigue in LP but not in HP cyclists. Novelty Caffeine improves exercise performance at the expense of a greater end-exercise peripheral fatigue in low-performing athletes. Caffeine-induced improvement in exercise performance does not affect end-exercise peripheral fatigue in high-performing athletes. High-performing athletes seem to have augmented tolerance to central fatigue during a high-intensity time trial.

Relationship between recovery of neuromuscular function and subsequent capacity to work above critical power.

PURPOSE: To investigate the relationship between the recovery of neuromuscular fatigue and the recovery of amount of work done above critical power (W´). METHODS: Ten healthy men performed, on different days, constant work rate exercises until task failure to determine critical power (CP) and W´. In the three following visits, participants performed two exhausting constant work rate exercises estimated to induce task failure within 6 min (P61 and P62), interspaced by 3, 6 or 15 min of recovery. Neuromuscular function was assessed before and periodically after the P61 using percutaneous electrical femoral nerve stimulation. The W´ recovery was measured from the total work performed above CP during the P62. RESULTS: The P61 induced a full use of W´ and a reduction in maximal voluntary contraction (MVC, - 19 ± 4%), voluntary activation (VA, - 6 ± 2%) and twitch force stimulated at 1 Hz (- 37 ± 11%), 10 Hz (- 50 ± 16%) and 100 Hz (- 32 ± 11%), when compared to baseline (P < 0.05). The time constant of VA recovery was significantly faster than the time constant of W´ recovery (P < 0.05), but there was no significant difference between the time constant of W´ recovery and the time constant of recovery of MVC or twitch force stimulated at 1, 10 and 100 Hz (P > 0.05). However, the time constant of W´ recovery was only associated to the time constant of MVC recovery (r = 0.73, P < 0.05). CONCLUSION: The W´ recovery is not associated to the recovery of peripheral or central fatigue alone. Rather, W´ seems to be associated to the recovery of the overall capacity to generate force.

Repetitions to failure versus not to failure during concurrent training in healthy elderly men: A randomized clinical trial.

This randomized clinical trial compared the neuromuscular adaptations induced by concurrent training (CT) performed with repetitions to concentric failure and not to failure in elderly men. Fifty-two individuals (66.2 ±â€¯5.2 years) completed the pre- and post-measurements and were divided into three groups: repetitions to failure (RFG, n = 17); repetitions not to failure (NFG, n = 20); and repetitions not to failure with total volume equalized to RFG (ENFG, n = 15). Participants were assessed in isometric knee extension peak torque (PTiso), maximal strength (1RM) in the leg press (LP) and knee extension (KE) exercises, quadriceps femoris muscle thickness (QF MT), specific tension, rate of torque development (RTD) at 50, 100 and 250 ms, countermovement jump (CMJ) and squat jump (SJ) performance, as well as maximal neuromuscular activity (EMGmax) of the vastus lateralis (VL) and rectus femoris (RF) muscles. CT was performed over 12 weeks, twice weekly. Along with each specific strength training program, each group also underwent an endurance training in the same session. After training, all groups improved similarly and significantly in LP and KE 1RM, PTiso, CMJ and SJ performance, RTD variables, specific tension, and VL EMGmax, (P < 0.05-0.001). QF MT improved only in RFG and ENFG (P < 0.01). These results suggest that repetitions until concentric failure does not provide further neuromuscular performance gains and muscle hypertrophy, and that even a low number of repetitions relative to the maximal possible (i.e., 50%) optimizes neuromuscular performance in elderly men. Moreover, training volume appears to be more important for muscle hypertrophy than training using maximal repetitions.

Caffeine increases both total work performed above critical power and peripheral fatigue during a 4-km cycling time trial.

The link between total work performed above critical power (CP) and peripheral muscle fatigue during self-paced exercise is unknown. We investigated the influence of caffeine on the total work done above CP during a 4-km cycling time trial (TT) and the subsequent consequence on the development of central and peripheral fatigue. Nine cyclists performed three constant-load exercise trials to determine CP and two 4-km TTs ~75 min after oral caffeine (5 mg/kg) or cellulose (placebo) ingestion. Neuromuscular functions were assessed before and 50 min after supplementation and 1 min after TT. Oral supplementation alone had no effect on neuromuscular function ( P > 0.05). Compared with placebo, caffeine increased mean power output (~4%, P = 0.01) and muscle recruitment (as inferred by EMG, ~17%, P = 0.01) and reduced the time to complete the TT (~2%, P = 0.01). Work performed above CP during the caffeine trial (16.7 ± 2.1 kJ) was significantly higher than during the placebo (14.7 ± 2.1 kJ, P = 0.01). End-exercise decline in quadriceps twitch force (pre- to postexercise decrease in twitch force at 1 and 10 Hz) was more pronounced after caffeine compared with placebo (121 ± 13 and 137 ± 14 N vs. 146 ± 13 and 156 ± 11 N; P < 0.05). There was no effect of caffeine on central fatigue. In conclusion, caffeine increases muscle recruitment, which enables greater work performed above CP and higher end-exercise peripheral locomotor muscle fatigue. NEW & NOTEWORTHY The link between total work done above critical power and peripheral fatigue during a self-paced, high-intensity exercise is unclear. This study revealed that caffeine ingestion increases muscle recruitment, which enables greater work done above critical power and a greater degree of end-exercise decline in quadriceps twitch force during a 4-km cycling time trial. These findings suggest that caffeine increases performance at the expense of greater locomotor muscle fatigue.

Hamstring-to-quadriceps fatigue ratio offers new and different muscle function information than the conventional non-fatigued ratio.

Commonly used injury risk prediction tests such as the hamstring-to-quadriceps (H:Q) strength ratio appear to be poor predictors of non-contact injury. However, these tests are typically performed in a non-fatigued state, despite accumulated fatigue being an important risk factor for both hamstring strain (HS) and anterior cruciate ligament (ACL) injuries in professional soccer players. After the effect of different H:Q calculation methods were compared and contrasted, the influence of neuromuscular fatigue on the H:Q strength ratio and the association between fatigued and non-fatigued ratio scores were examined. Thirty-five professional soccer players performed a 30-repetition isokinetic fatigue test protocol. Peak knee joint moments were computed for each repetition, and the H:Q conventional ratio (H:QCR ) was calculated using several different, previously published, methods. Knee extensor and flexor moments were statistically decreased by the sixth repetition and continued to decrease until the end of the protocol. However, the H:Q ratio was statistically decreased at the end of the test due to a significant reduction in knee flexor moment (correlation between change in knee flexor moment and change in H:Q, r≈.80; P<.01). Moreover, H:Q measured in fatigue (ie, H:QFatigue ) at the end of the test was greater than H:QCR (1.25-1.38 vs 0.70, P<.01), these variables were weakly correlated (r=.39, P=.02), and subject rankings within the cohort based on H:QCR and H:QFatigue were different (rs =0.25, P=.15). The present data suggest that H:Q ratio measurement during a fatiguing test (H:QFatigue ) provides different outcomes to the traditional H:QCR . The observed significant hamstring fatigue and the difference, and weak correlation, between H:QCR and H:QFatigue indicate that useful information might be obtained with respect to the prediction of HS and ACL injury risk. The potential predictive value of H:QFatigue warrants validation in future prospective trials.

Effects of fatigue on lower limb, pelvis and trunk kinematics and lower limb muscle activity during single-leg landing after anterior cruciate ligament reconstruction.

PURPOSE: Because there are no studies that have evaluated the effects of fatigue on the kinematics of the trunk and pelvis or on muscle activation in subjects with ACL reconstruction, the aim of this study was to evaluate the effects of fatigue on the lower limb, pelvis and trunk kinematics and lower limb muscle activation in subjects with ACL reconstruction during a single-leg landing compared to a healthy control group. METHODS: The participants included 20 subjects with ACL reconstruction (ACL reconstruction group-ACLRG) and 20 healthy subjects (control group-CG) who were aged between 18 and 35 years. Kinematic and electromyographic analyses were performed during a single-leg landing before and after fatigue. The fatigue protocol included a series of 10 squats, two vertical jumps, and 20 steps. RESULTS: The effects of fatigue were increased peak trunk flexion and increased activation of the vastus lateralis, biceps femoris (BF) and gluteus maximus (GMax) during the landing phase. CONCLUSION: After the fatigue protocol, an increase in peak trunk flexion and activation of the GMax and BF were observed, most likely as a strategy to reduce the load on the ACL. ACL injury prevention programs should include strength and endurance exercises for the hip and trunk extensor muscles so that they can efficiently control trunk flexion during landing. LEVEL OF EVIDENCE: Prospective comparative study, Level II.

Effects of fatigue on lower limb, pelvis and trunk kinematics and muscle activation: Gender differences.

BACKGROUND: Muscle fatigue is associated with biomechanical changes that may lead to anterior cruciate ligament (ACL) injuries. Alterations in trunk and pelvis kinematics may also be involved in ACL injury. Although some studies have compared the effects of muscle fatigue on lower limb kinematics between men and women, little is known about its effects on pelvis and trunk kinematics. The aim of the study was to compare the effects of fatigue on lower limb, pelvis and trunk kinematics and muscle activation between men and women during landing. METHODS: The participants included forty healthy subjects. We performed kinematic analysis of the trunk, pelvis, hip and knee and muscle activation analysis of the gluteal muscles, vastus lateralis and biceps femoris, during a single-leg landing before and after fatigue. RESULTS: Men had greater trunk flexion than women after fatigue. After fatigue, a decrease in peak knee flexion and an increase in Gmax and BF activation were observed. CONCLUSION: The increase in the trunk flexion can decrease the anterior tibiofemoral shear force resulted from the lower knee flexion angle, thereby decreasing the stress on the ACL.

EFFECT OF DIFFERENT FOAM ROLLING VOLUMES ON KNEE EXTENSION FATIGUE.

BACKGROUND: Foam rolling (FR) is a common intervention utilized for the purpose of acutely increasing range-of-motion without subsequent decreases in performance. FR is characterized as an active technique which subject performs upon themselves. Thus, it is believed that the accumulated fatigue can influence whether the task can be continued. PURPOSE: To analyze the effect of different foam rolling volumes on fatigue of the knee extensors. METHODS: Twenty-five recreationally active females (age 27.7 ± 3.56 y, height 168.4 ± 7.1 cm, weight 69.1 ± 10.2 kg) were recruited for the study. The experiment involved three sets of knee extensions with a pre-determined 10 repetition maximum load to concentric failure. Then, subjects performed the control (CONT) and foam rolling (FR) conditions. FR conditions consisted of different anterior thigh rolling volumes (60-, 90-, and 120-seconds) which were performed during the inter-set rest period. After that, the fatigue index was calculated and compared between each experimental condition. Fatigue index indicates how much (%) resistance the subjects experienced, calculated by the equation: (thidset/firstset) x 100. RESULTS: Fatigue index was statistically significantly greater (greater fatigue resistance) for CONT compared to FR90 (p = 0.001) and FR120 (p = 0.001). Similarly, higher fatigue resistance was observed for FR60 when compared to FR120 (p = 0.048). There were no significant differences between the other conditions (p > 0.005). CONCLUSION: The finding of foam rolling fatigue index decline (less fatigue resistance) as compared to control conditions may have implications for foam rolling prescription and implementation, in both rehabilitation and athletic populations. For the purposes of maximum repetition performance, foam rolling should not be applied to the agonist muscle group between sets of knee extensions. Moreover, it seems that volumes greater than 90-seconds are detrimental to the ability to continually produce force. LEVEL OF EVIDENCE: 2b.

A influência da fadiga neuromuscular e da acidose metabólica sobre a corrida de 400 metros / Influence of neuromuscular fatigue and metabolic acidosis on the 400-meter race

Exercícios inabituais podem levar a danos musculares que persistem por alguns dias diminuindo a capacidade de desempenho em decorrência da fadiga. Além disso, o aumento da acidose intramuscular pode limitar o metabolismo celular no processo de gerar trabalho. Com isso, esta pesquisa teve como finalidade analisar a influência da fadiga neuromuscular e da acidose metabólica sobre a corrida de 400 metros. Foram selecionados 20 indivíduos, sedentários, com idade entre 18 e 35 anos. Estes foram submetidos aos seguintes protocolos: teste incremental em esteira, para determinação do VO2max; limiares aeróbio e anaeróbio, teste de 400m (400/C), atividade pliométrica, com repouso ativo/passivo, seguida de corrida de 400m logo após (400/Pós) e 24 horas após a atividade pliométrica (400/24h). Os resultados obtidos mostram que, quando comparados os grupos ativo e passivo, não apresentaram diferenças significantes no desempenho dos 400/ Pós, mas o tempo deste foi maior, para os dois grupos quando comparado com os 400/C. No entanto, o 400/24h não foi significantemente diferente quando comparado com o 400/C para ambos os grupos. Concluise que, independente do tipo de recuperação - ativa ou passiva -, a diminuição de desempenho em uma corrida de 400 metros após atividade pliométrica parece ser ocasionada por mecanismos neuromusculares que levam à fadiga e não a limitações metabólicas.

Unusual exercises can lead to muscle damage that persists for a few days reducing performance ability due to fatigue onset. Moreover, intramuscular acidity increase can limit the cell metabolism in the process of producing work. Therefore, the objective of this research was to analyze the influence of neuromuscular fatigue and metabolic acidity in the 400 m race. The selected sample consisted of 20 sedentary individuals, aged between 18 and 35 years. They were submitted to the following protocols: treadmill incremental test for determination of VO2max; aerobic and anaerobic threshold; 400m race test (400/R); plyometric activity with active/passive rest followed by 400m race immediately after (400/Post) and 24 hours after the plyometric activity (400/24h). The obtained results show that when the active and passive groups are compared, they do not show significant difference in 400/Post performance, but this time was longer for both groups when compared with the 400/R. Nevertheless, the 400/24h was not significantly different when compared with the 400/R to both groups. It was concluded that regardless of the kind of recovery, active or passive, the performance reduction in a 400-meter race after plyometric activity seems to occur by neuromuscular mechanisms that lead to fatigue and not to metabolic limitations.