The Effect of Duration on Performance and Perceived Fatigability During Acute High-Intensity Interval Exercise in Young, Healthy Males and Females.

Few studies have explored the kinetics of performance and perceived fatigability during high-intensity interval training, despite its popularity. We aimed to characterize the kinetics of fatigability and recovery during an 8 × 4-min HIIT protocol, hypothesizing that most muscle function impairment would occur during the initial four intervals. Fifteen healthy males and females (mean ± standard deviation; age = 26 ± 5 years, V̇O2max = 46.8 ± 6.1 mL·kg-1·min-1) completed eight, 4-min intervals at 105% of critical power with 3 min of rest. Maximal voluntary knee extension contractions (MVCs) coupled with electrical nerve stimulation were performed at baseline and after the first, fourth, and eighth intervals. MVC, potentiated twitch force (Pt), and Db10:100 ratio all declined throughout HIIT (p < 0.05). MVC sharply declined after interval 1 (-15 ± 9% relative to baseline; p < 0.05) and had only further declined after interval 8 (-26 ± 11%; p < 0.05), but not interval 4 (-19 ± 13%; p > 0.05). Pt and Db10:100 also sharply declined after interval 1 (Pt: -18 ± 13%, Db10:100: -14 ± 20%; p < 0.05) and further declined after interval 4 (Pt: -35 ± 19%, Db10:100: -30 ± 20%; p < 0.05) but not interval 8 (Pt: -41 ± 19%; Db10:100: -32 ± 18%; p > 0.05). Voluntary activation did not significantly change across the HIIT protocol (p > 0.05). Evoked force recovery was significantly blunted as more intervals were completed: after interval 1, Pt recovered by 7 ± 11% compared to -6 ± 7% recovery after interval 8 (p < 0.05). Ratings of perceived effort, fatigue, and leg pain rose throughout the session (p < 0.05 for each) and were greater (effort and fatigue) for females (p < 0.05). Otherwise, males and females exhibited similar performance fatigability kinetics, with contractile function declines blunted in response to additional intervals.

Acute neuromuscular, cardiovascular, and muscle oxygenation responses to low-intensity aerobic interval exercises with blood flow restriction.

We investigated the influence of short- and long-interval cycling exercise with blood flow restriction (BFR) on neuromuscular fatigue, shear stress and muscle oxygenation, potent stimuli to BFR-training adaptations. During separate sessions, eight individuals performed short- (24 × 60 s/30 s; SI) or long-interval (12 × 120 s/60 s; LI) trials on a cycle ergometer, matched for total work. One leg exercised with (BFR-leg) and the other without (CTRL-leg) BFR. Quadriceps fatigue was quantified using pre- to post-interval changes in maximal voluntary contraction (MVC), potentiated twitch force (QT) and voluntary activation (VA). Shear rate was measured by Doppler ultrasound at cuff release post-intervals. Vastus lateralis tissue oxygenation was measured by near-infrared spectroscopy during exercise. Following the initial interval, significant (P < 0.05) declines in MVC and QT were found in both SI and LI, which were more pronounced in the BFR-leg, and accounted for approximately two-thirds of the total reduction at exercise termination. In the BFR-leg, reductions in MVC (-28 ± 15%), QT (-42 ± 17%), and VA (-15 ± 17%) were maximal at exercise termination and persisted up to 8 min post-exercise. Exercise-induced muscle deoxygenation was greater (P < 0.001) in the BFR-leg than CTRL-leg and perceived pain was more in LI than SI (P < 0.014). Cuff release triggered a significant (P < 0.001) shear rate increase which was consistent across trials. Exercise-induced neuromuscular fatigue in the BFR-leg exceeded that in the CTRL-leg and was predominantly of peripheral origin. BFR also resulted in diminished muscle oxygenation and elevated shear stress. Finally, short-interval trials resulted in comparable neuromuscular and haemodynamic responses with reduced perceived pain compared to long-intervals.

Hydrogen-rich water supplementation promotes muscle recovery after two strenuous training sessions performed on the same day in elite fin swimmers: randomized, double-blind, placebo-controlled, crossover trial.

Purpose: Molecular hydrogen has been shown to possess antioxidant, anti-inflammatory, ergogenic, and recovery-enhancing effects. This study aimed to assess the effect of molecular hydrogen administration on muscle performance, damage, and perception of soreness up to 24 h of recovery after two strenuous training sessions performed on the same day in elite fin swimmers. Methods: Eight females (mean ± SD; age 21.5 ± 5.0 years, maximal oxygen consumption 45.0 ± 2.5 mL.kg-1.min-1) and four males (age 18.9 ± 1.3 years, maximal oxygen consumption 52.2 ± 1.7 mL.kg-1.min-1) performed 12 × 50 m sprints in the morning session and a 400 m competitive performance in the afternoon session. Participants consumed hydrogen-rich water (HRW) or placebo 3 days before the sessions (1,260 mL/day) and 2,520 mL on the experimental day. Muscle performance (countermovement jump), muscle damage (creatine kinase), and muscle soreness (100 mm visual analogue scale) were measured during the experimental day and at 12 and 24 h after the afternoon session. Results: HRW compared to placebo reduced blood activity of creatine kinase (156 ± 63 vs. 190 ± 64 U.L-1, p = 0.043), muscle soreness perception (34 ± 12 vs. 42 ± 12 mm, p = 0.045), and improved countermovement jump height (30.7 ± 5.5 cm vs. 29.8 ± 5.8 cm, p = 0.014) at 12 h after the afternoon session. Conclusion: Four days of HRW supplementation is a promising hydration strategy for promoting muscle recovery after two strenuous training sessions performed on the same day in elite fin swimmers. Clinical Trial Registration: clinicaltrials.gov, identifier NCT05799911.

Acute effects of caffeine or quercetin ingestion on motor unit firing pattern before and after resistance exercise.

The aim of the present study was to investigate the acute effect of caffeine or quercetin ingestion on motor unit firing patterns and muscle contractile properties before and after resistance exercise. High-density surface electromyography (HDs-EMG) during submaximal contractions and electrically elicited torque in knee extensor muscles were measured before (PRE) and 60 min after (POST1) ingestion of caffeine, quercetin glycosides, or placebo, and after resistance exercise (POST2) in ten young males. The Convolution Kernel Compensation technique was used to identify individual motor units of the vastus lateralis muscle for the recorded HDs-EMG. Ingestion of caffeine or quercetin induced significantly greater decreases in recruitment thresholds (RTs) from PRE to POST1 compared with placebo (placebo: 94.8 ± 9.7%, caffeine: 84.5 ± 16.2%, quercetin: 91.9 ± 36.7%), and there were significant negative correlations between the change in RTs (POST1-PRE) and RT at PRE for caffeine (rs = - 0.448, p < 0.001) and quercetin (rs = - 0.415, p = 0.003), but not placebo (rs = - 0.109, p = 0.440). Significant positive correlations between the change in firing rates (POST2-POST1) and RT at PRE were noted with placebo (rs = 0.380, p = 0.005) and quercetin (rs = 0.382, p = 0.007), but not caffeine (rs = 0.069, p = 0.606). No significant differences were observed in electrically elicited torque among the three conditions. These results suggest that caffeine or quercetin ingestion alters motor unit firing patterns after resistance exercise in different threshold-dependent manners in males.

Females show less decline in contractile function than males after repeated all-out cycling.

Females demonstrate greater fatigue resistance during a range of exercise modalities; however, this may be confounded by the lower mechanical work completed. Accordingly, this study examined the sex-specific peripheral and central fatigue mechanisms during repeated all-out cycling and whether they are affected by total mechanical work performed. A total of 26 healthy young adults (12 females) performed 10 × 10 s all-out cycling interspersed by 30 s passive recovery. Metabolic responses, peripheral and central fatigue, were quantified via changes in pre- to post-exercise blood lactate, potentiated quadriceps twitch force (and contractile properties) evoked via supramaximal electrical stimulation of the femoral nerve, and voluntary activation of the knee extensors, respectively. During exercise, mechanical work, vastus lateralis muscle activation (via surface electromyography), and deoxygenation (via near-infrared spectroscopy) were recorded. Sex comparison analyses were performed before and after statistically controlling for total mechanical work (via ANCOVA). Mechanical work and muscle activation plateaued at similar sprint repetition (sprint 5) and voluntary activation change (pre vs. post) was similar between the sexes. Females, however, showed lower %work decrement (i.e., fatigability; P = 0.037) and peripheral responses as evident by lower reductions in quadriceps twitch force (P < 0.001) and muscle deoxygenation (P = 0.001). Adjusting for total mechanical work did not change these sex comparison results. We show that females' greater fatigue resistance during repeated all-out cycling may not be attributed to the greater total mechanical work performed but could be mediated by lower peripheral fatigue in the knee extensor muscles.

Quadriceps fatigue during hypoxic and ischemic knee-extension exercise is similar in males and females.

Hypoxia is known to increase muscle fatigue via both central and peripheral mechanisms. Females are typically less fatigable than males during isometric fatiguing contractions due to greater peripheral blood flow. However, sex differences in fatigue are blunted during dynamic fatiguing tasks. Thus, this study determined the interactions of sex and hypoxia on knee extensor muscle contractile function during a dynamic, ischemic fatiguing contraction. Electrical stimulation was used to determine contractile properties of the knee extensor muscles in eight males and eight females before and after an ischemic, dynamic fatiguing task while inspiring room air or a hypoxic gas mixture (10% O2:90% N2). Fatigue (assessed as time-to-task failure) was ∼10% greater during the hypoxic condition (94.3 ± 33.4 s) compared with normoxic condition (107.0 ± 42.8 s, P = 0.041) and ∼40% greater for females than males (77.1 ± 18.8 vs. 124.2 ± 38.7, P < 0.001). Immediately after the dynamic fatiguing task, there were reductions in maximal voluntary contraction force (P = 0.034) and electrically evoked twitch force (P < 0.001), and these reductions did not differ based on sex or inspirate. Cerebral tissue oxygenation showed a significant interaction of time and inspirate (P = 0.003) whereby it increased during normoxia and remained unchanged in hypoxia. No sex-related differences in the changes of cerebral tissue oxygenation were observed (P = 0.528). These data suggest that acute hypoxia increases central fatigue during ischemic single-leg exercise resulting in earlier exercise termination, but the effect does not differ based on sex.NEW & NOTEWORTHY Hypoxia exacerbates fatigue via central mechanisms after ischemic single-leg exercise. The greater fatigue observed during ischemic dynamic fatiguing exercise with hypoxia inspirate did not differ between the sexes. Hypoxia-induced central limitations are present in acute ischemic exercise and do not appear different in males and females.

Performance Kinetics During Repeated Sprints is Influenced by Knowledge of Task Endpoint and Associated Peripheral Fatigue.

The regulation of exercise intensity allows an athlete to perform an exercise in the fastest possible time while avoiding debilitating neuromuscular fatigue development. This phenomenon is less studied during intermittent activities. To investigate anticipatory and real-time regulation of motor output and neuromuscular fatigue during repeated-sprint exercise, twelve males randomly performed one (S1), two (S2), four (S4) and six (S6) sets of five 5-s cycling sprints. Mechanical work and electromyographic activity were assessed during sprints. Potentiated quadriceps twitch force (ΔQtw,pot) and central activation ratio (QCAR) were quantified from response to supra-maximal magnetic femoral nerve stimulation pre-vs post-exercise. Compared with S1, mechanical work developed in the first sprint and in the entire first set was reduced in S6 (-7.8% and -5.1%, respectively, P < 0.05). Work developed in the last set was similar in S4 and S6 (P = 0.82). Similar results were observed for EMG activity. The QCAR was also more reduced in S4 (-5.8%, P < 0.05) and S6 (-8.3%, P < 0.05) than in S1. However, ΔQtw,pot was not significantly different across all trials (-33.1% to -41.9%, P = 0.46). Perceived exhaustion increased across sprints to reach a maximal and similar level in S2, S4 and S6 (all 19.2, P < 0.01 vs S1). These results suggest that the regulation of performance, exerted at the beginning and continuously during repeated sprints, is based on the task endpoint, presumably to avoid excessive peripheral muscle and associated conscious overwhelming sensations.

Different ramp-incremental slopes elicit similar V̇o2max and fatigability profiles in females and males despite differences in peak power output.

The aim of this article is to investigate the effects of different ramp-incremental (RI) slopes on fatigability and its recovery in females and males. Ten females and 11 males performed RI tests with distinct slopes, in separated and randomized sessions, 15 (RI15), 30 (RI30), and 45 (RI45) W·min-1. Performance fatigability was assessed by femoral nerve electrical stimuli evoked during and after isometric maximal voluntary contraction (IMVC) of knee extensors at baseline and after task failure at min 0.5, 1.5, 2.5, 5, and 10. Maximal oxygen uptake (V̇o2max) and peak power output (POpeak) were also measured. There were significant and similar declines from pre- to post-RI test in RI15, RI30, and RI45 for IMVC (-23%; -25%; -25%, respectively; P < 0.05) and potentiated single twitch (-46%; -47%; -49%; P < 0.05), whereas voluntary activation did not change (-1%; -1%; 0%; P > 0.05). There were no RI condition effects, nor time × condition interaction for IMVC, potentiated single twitch and voluntary activation (all P > 0.05). V̇o2max was not different among RI15, RI30, and RI45 conditions (3.30, 3.29, and 3.26 L·min-1, respectively; P = 0.717), but POpeak was (272, 304, and 337 W, respectively; P < 0.001). Overall, performance fatigability profiles were similar between sexes after the RI tests and during recovery. In addition, during recovery, high-frequency doublets and single twitch recovered faster after RI30 and RI45 compared with RI15, regardless of sex (all P > 0.05 for sex differences). In conclusion, RI tests of different slopes that elicited similar V̇o2max but different POpeak did not affect the profile of performance fatigability at task failure in females and males.NEW & NOTEWORTHY It was unknown whether performance fatigability and its recovery are affected by different slopes in a ramp incremental (RI) test. It was also uncertain if females and males would respond differently. Performance fatigability was the same regardless of the RI slope adopted and the sex of the population, which was accompanied by similar maximal oxygen uptake but different power output achieved. The recovery of contractile function was similar between sexes but delayed after slower RI slopes.

Exacerbated central fatigue and reduced exercise capacity in early-stage breast cancer patients treated with chemotherapy.

PURPOSE: The present study aimed to characterize the etiology of exercise-induced neuromuscular fatigue and its consequences on the force-duration relationship to provide mechanistic insights into the reduced exercise capacity characterizing early-stage breast cancer patients. METHODS: Fifteen early-stage breast cancer patients and fifteen healthy women performed 60 maximal voluntary isometric quadriceps contractions (MVCs, 3 s of contraction, 2 s of relaxation). The critical force was determined as the mean force of the last six contractions, while W' was calculated as the force impulse generated above the critical force. 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) evoked by supramaximal electrical stimulation, respectively. RESULTS: Early-stage breast cancer patients demonstrated lower MVC than controls preexercise (- 15%, P = 0.022), and this reduction persisted throughout the 60-MVC exercise (- 21%, P = 0.002). The absolute critical force was lower in patients than in controls (144 ± 29N vs. 201 ± 47N, respectively, P < 0.001), while W' was similar (P = 0.546), resulting in lower total work done (- 23%, P = 0.001). This was associated with lower muscle activation in the vastus lateralis (P < 0.001), vastus medialis (P = 0.003) and rectus femoris (P = 0.003) in patients. Immediately following exercise, ΔVA showed a greater reduction in patients compared to controls (- 21.6 ± 13.3% vs. - 12.6 ± 7.7%, P = 0.040), while ΔQTw was similar (- 60.2 ± 13.2% vs. - 52.8 ± 19.4%, P = 0.196). CONCLUSION: These findings support central fatigue as a primary cause of the reduction in exercise capacity characterizing early-stage breast cancer patients treated with chemotherapy. CLINICAL TRIALS REGISTRATION: No. NCT04639609-November 20, 2020.

Complete recovery of quadriceps muscle peripheral fatigue after running in Olympic, but not Sprint, triathlon.

This study compared central and peripheral fatigue development between the Sprint and Olympic distance triathlon. Fifteen male triathletes performed Sprint and Olympic triathlon simulations in a randomized and counterbalanced order. Central and peripheral fatigue was evaluated from changes in voluntary activation level (VAL) and twitch responses of quadriceps muscle (Qtw,pot), respectively. Qtw,pot reduced from baseline to post-swimming similarly between triathlon simulations (Sprint,-17±11%; Olympic, -13±9%). In post-cycling, Qtw,pot further declined to a similar extent between triathlon distances (Sprint, -31±15%; Olympic, -28±11%). In post-running, Qtw,pot was fully recovered in the Olympic triathlon (-4±10%), whereas there was only a partial recovery of Qtw,pot in the Sprint triathlon (-20±11%). VAL was not reduced in post-swimming, but reduction was similar between triathlon distances in post-cycling (Sprint, -10±9%; Olympic, -8±8%) and post-running (Sprint, -15±14%; Olympic, -16±8%). In the Sprint triathlon, the swimming speed (1.07±0.13m.s-1) was above (p <.001) critical speed (1.01±0.14m.s-1), the cycling power (179.7±27.2W) was below the respiratory compensation point (216.3±27.8W, p <.001) and running speed (13.7±1.05km.h-1) similar to the respiratory compensation point (13.2±0.70km.h-1, p =.124). In the Olympic triathlon, swimming speed (1.03±0.13m.s-1) was similar to critical speed (p =.392), and cycling power (165.3±27.3W) and running speed (12.6±1.05km.h-1) were below the respiratory compensation point (p ≤.007). In conclusion, peripheral fatigue progressed until post-cycling regardless of triathlon distances. However, peripheral fatigue was fully recovered after running in Olympic but not in Sprint triathlon. The central fatigue started in post-cycling and progressed until post-running regardless of triathlon distances.HighlightsThe quadriceps muscle peripheral fatigue progresses similarly in Sprint and Olympic triathlons until post-cycling.The quadriceps muscle peripheral fatigue is completely recovered after running in the Olympic triathlon, whereas it is partially recovered in the Sprint triathlon.The central fatigue starts in post-cycling and progresses similarly until post-running in Sprint and Olympic triathlons, regardless of triathlon distances.

Blood flow restriction during self-paced aerobic intervals reduces mechanical and cardiovascular demands without modifying neuromuscular fatigue.

This study examined cardiovascular, perceptual and neuromuscular fatigue characteristics during and after cycling intervals with and without blood flow restriction (BFR). Fourteen endurance cyclists/triathletes completed four 4-minute self-paced aerobic cycling intervals at the highest sustainable intensity, with and without intermittent BFR (60% of arterial occlusion pressure). Rest interval durations were six, four and four minutes, respectively. Power output, cardiovascular demands and ratings of perceived exertion (RPE) were averaged over each interval. Knee extension torque and vastus lateralis electromyography responses following electrical stimulation of the femoral nerve were recorded pre-exercise, post-interval one (+1, 2 and 4-minutes) and post-interval four (+1, 2, 4, 6 and 8-minutes). Power output during BFR intervals was lower than non-BFR (233 ± 54 vs 282 ± 60 W, p < 0.001). Oxygen uptake and heart rate during BFR intervals were lower compared to non-BFR (38.7 ± 4.5 vs 44.7 ± 6.44 mL kg-1 min-1, p < 0.001; 160 ± 14 vs 166 ± 10 bpm, p < 0.001), while RPE was not different between conditions. Compared to pre-exercise, maximal voluntary contraction torque and peak twitch torque were reduced after the first interval with further reductions following the fourth interval (p < 0.001) independent of condition (p = 0.992). Voluntary activation (twitch interpolation) did not change between timepoints (p = 0.375). Overall, intermittent BFR reduced the mechanical and cardiovascular demands of self-paced intervals without modifying RPE or knee-extensor neuromuscular characteristics. Therefore, BFR reduced the cardiovascular demands while maintaining the muscular demands associated with self-paced intervals. Self-paced BFR intervals could be used to prevent cardiovascular and perceptual demands being the limiting factor of exercise intensity, thus allowing greater physiological muscular demands compared to intervals without BFR.HighlightsThe use of blood flow restriction (BFR) during self-paced intervals (at the highest perceived sustainable intensity) causes a reduction in power output, pulmonary oxygen uptake and heart rate compared with non-restricted self-paced intervals.Despite lower mechanical and physiological demands during BFR cycling, the magnitude and aetiology of neuromuscular fatigue were not different to intervals without BFR, indicating the internal muscular load during BFR was elevated and potentially equivalent compared to without BFR.Self-paced intervals could be a suitable model to prescribe aerobic BFR exercise as an adjunct training stimulus for endurance cyclists.

Knee position sense and knee flexor neuromuscular function are similarly altered after two submaximal eccentric bouts.

PURPOSE: This study examined eccentric-induced fatigue effects on knee flexor (KF) neuromuscular function and on knee position sense. This design was repeated across two experimental sessions performed 1 week apart to investigate potential repeated bout effects. METHODS: Sixteen participants performed two submaximal bouts of KF unilateral eccentric contractions until reaching a 20% decrease in maximal voluntary isometric contraction force. Knee position sense was evaluated with position-matching tasks in seated and prone positions at 40° and 70° of knee flexion so that KF were either antagonistic or agonistic during the positioning movement. The twitch interpolation technique was used to assess KF neuromuscular fatigue. Perceived muscle soreness was also assessed. Measurements were performed before, immediately (POST) and 24 h after (POST24) each eccentric bout. RESULTS: No repeated bout effect on neuromuscular function and proprioceptive parameters was observed. At POST, central and peripheral factors contributed to the force decrement as shown by significant decreases in voluntary activation level (- 3.8 ± 4.8%, p < 0.01) and potentiated doublet torque at 100 Hz (- 10 ± 15.8%, p < 0.01). At this time point, position-matching errors significantly increased by 1.7 ± 1.9° in seated position at 40° (p < 0.01). At POST24, in presence of muscle soreness (p < 0.05), although KF neuromuscular function had recovered, position-matching errors increased by 0.6 ± 2.6° in prone position at 40° (p < 0.01). CONCLUSION: These results provide evidence that eccentric-induced position sense alterations may arise from central and/or peripheral mechanisms depending on the testing position.

No sex differences in evoked contractile properties after fatiguing isometric and isotonic exercise for the plantar flexors.

OBJECTIVES: Females tend to fatigue less than males after isometric exercise, but less is clear for isotonic exercise. Further, there have been relatively few sex comparisons for fatigability of the plantar flexors (PFs). We sought to investigate potential sex differences in contractile properties after a sustained maximal voluntary isometric contraction (MVIC) and isotonic contractions. METHODS: Twenty-seven physically active males (n=14; 22±2 yrs) and females (n=13; 21±2 yrs) randomly performed a 2 min MVIC and 120 concentric isotonic (30% MVIC) contractions for the PFs on separate visits. Before and after each fatiguing task, muscle activation was obtained from brief MVICs, which was followed (~2 sec) by tibial nerve stimulation at rest. Contractile properties including peak twitch, absolute and normalized time to peak twitch, and half relaxation time were calculated. RESULTS: No sex differences existed for fatigue-induced changes in muscle activation (p=0.09-0.41; d=0.33-0.69) or contractile properties (p=0.19-0.96; d=0.06-0.94). CONCLUSIONS: Peripheral fatigue, as indicated by contractile parameters, did not differ between sexes after isometric or isotonic exercise. The PFs similar fiber type proportions between sexes or greater fiber type heterogeneity may explain why sex differences in fatigability, though common in other muscle groups (e.g., knee extensors), were not expressed in this muscle group.

Performance fatigability during isometric vs. concentric quadriceps fatiguing tasks in men and women.

In the present study, we aimed to provide a robust comparison of the fatigability of the knee extensors following isometric (ISO) and concentric (CON) tasks. Twenty young adults (25 ± 4 yr, 10 women) randomly performed the ISO and CON quadriceps intermittent fatigue test, consisting of ten (5 s on/5-s off, ISO) or one-hundred (0.5-s on/0.5-s off, CON) contractions with 10 % increments per stage until exhaustion. Performance fatigability was quantified as maximal isometric (MVIC) and concentric (MVCC) torque loss. Voluntary activation and contractile function (peak-twitch) were investigated using peripheral nerve stimulation. Number of stages (6.2 ± 0.7 vs. 4.9 ± 0.8; P < 0.001) and torque-time integral (20,166 ± 7,821 vs. 11,285 ± 4,933 Nm.s; P < 0.001) were greater for ISO than CON. MVIC, MVCC and voluntary activation decreased similarly between sessions (P > 0.05) whereas peak-twitch amplitude decreased more for CON (P < 0.001). The number of contractions was similar across sexes (ISO: men = 62 ± 8, women = 61 ± 5; CON: men = 521 ± 67, women = 458 ± 76, P > 0.05). MVCC was more reduced in women for both sessions (all P < 0.05), while MVIC loss was similar between sexes. We concluded that, despite greater torque-time integral and duration for ISO, both sessions induced a similar performance fatigability at exhaustion. Contractile function was more altered in CON. Finally, sex-related difference in fatigability depends on the contraction mode used during testing.

Effect of Six-Week Speed Endurance Training on Peripheral Fatigue.

(1) Speed endurance training (inducing a high blood lactate concentration) delays excitation-contraction coupling impairment, thus providing more space for high-frequency fatigue to occur in the early stage of maximal concentric actions. This study aimed to test the hypothesis that the maintenance type of speed endurance training may shift peripheral fatigue from low-frequency to high-frequency fatigue after the 15 s long Wingate test. (2) Six students of physical education performed the corresponding training for six weeks. Before and after this period, they were tested for low- and high-frequency fatigue after the 15 s long Wingate test; additionally, their blood lactate concentrations, maximal cycling power, work, fatigue index, and muscle twitch responses were also tested. (3) The training increased the maximal cycling power and work (p < 0.001 and p < 0.01, respectively) with minor changes in the mean fatigue index and blood lactate concentration (both p > 0.05). Low-frequency dominant fatigue before the training showed a trend toward high-frequency dominant fatigue after the training (p > 0.05). (4) The results showed that the 15 s Wingate test failed to induce significant high-frequency fatigue. Even though it displayed a substantial fatigue index, the changes in favor of high-frequency fatigue were too small to be relevant.

Understanding fatigue in primary biliary cholangitis: From pathophysiology to treatment perspectives.

Fatigue is considered one of the most frequent and debilitating symptoms in primary biliary cholangitis (PBC), affecting over 50% of PBC patients. One in five patients with PBC suffer from severe fatigue, which significantly impairs quality of life. Fatigue is made up of a central and a peripheral component, whose pathophysiology is still greatly unresolved. Central fatigue is characterised by a lack of self-motivation and can manifest both in physical and mental activities (lack of intention). Peripheral fatigue includes neuromuscular dysfunction and muscle weakness (lack of ability). Peripheral fatigue could be explained by an excessive deviation from aerobic to anaerobic metabolism leading to excessive lactic acid accumulation and therefore accelerated decline in muscle function and prolonged recovery time. As opposed to itching, and with the exception of end-stage liver disease, fatigue is not related to disease progression. The objective of this review is to outline current understanding regarding the pathophysiology of fatigue, the role of comorbidities and contributing factors, the main tools for fatigue assessment, the failed therapeutic options, and future treatment perspectives for this disabling symptom. Since fatigue is an extremely common and debilitating symptom and there is still no licensed therapy for fatigue in PBC patients, further research is warranted to understand its causative mechanisms and to find an effective treatment.

Sex differences in central and peripheral fatigue induced by sustained isometric ankle plantar flexion.

The main aim of this study was to determine sex differences in central and peripheral fatigue produced by a sustained isometric exercise of ankle plantar flexors in healthy young adults. Ten males and fourteen females performed a sustained isometric ankle exercise until task failure. Maximal voluntary isometric contraction (MVIC) torque (plantarflexion), voluntary activation level (using the twitch interpolation technique), and resting twitch contractile properties [twitch peak torque (ST), twitch half relaxation time, and low frequency fatigue (LFF) ratio] were measured before, immediately after, and throughout a recovery period (1, 2, 5, and 10 min) following the exercise protocol in order to characterize neuromuscular fatigue. Fatigue had effects (p≤ 0.05) on all dependent variables (reduction in MVIC, VA and twitch torque and slowing of relaxation time). However, no significant differences in performance fatigability markers (MVIC torque decline and time to fatigue) and only minor differences in the variables reflecting central and peripheral fatigue mechanisms were found between males and females. A regression analysis did suggest a somewhat greater role of central fatigue in males compared with females. Females also showed a slightly greater and more prolonged decline in ST and LFF after exercise compared with males. The presence of only minor differences in central and peripheral fatigue mechanisms between males and females in the present study could be explained by the lack of important sex differences in performance fatigability, which could be due to lesser sex differences in the relative area of type I muscle fibers and in contractile function (muscle strength) of ankle plantar flexors as compared with other muscle groups.

Neuromuscular and perceptual mechanisms of fatigue accompanying task failure in response to moderate-, heavy-, severe-, and extreme-intensity cycling.

A comprehensive characterization of neuromuscular and perceptual mechanisms of fatigue at task failure following exercise across the entire intensity spectrum is lacking. This study evaluated the extent of peripheral and central fatigue, and corresponding perceptual attributes, at task failure following cycling within the moderate-(MOD), heavy-(HVY), severe-(SVR), and extreme-(EXT) intensity domains. After a ramp-incremental test, 11 young males performed four constant-power output trials to the limit of tolerance (Tlim) at 4 distinct domain-specific workloads. These trials were preceded and followed by 5-s knee-extension maximal voluntary contractions (MVCs) and femoral nerve electrical stimuli to quantify peripheral and central fatigue. In addition, perceptual measures including ratings of global fatigue, legs pain, dyspnea, and perceived effort (RPE) were also collected. At Tlim, reductions in MVC were independent of intensity (P > 0.05). However, peripheral fatigue was greater following EXT and SVR and progressively, but distinctively, lower following HVY and MOD (P < 0.05). Central fatigue was similar after SVR, HVY, and MOD, but absent after EXT (P < 0.05). At Tlim, subjective ratings of global fatigue were progressively higher with lower exercise intensities, whereas ratings of legs pain and dyspnea were progressively higher with higher exercise intensities. On the other hand, RPE was maximal following HVY, SVR, and EXT, but not MOD. The findings demonstrate that at Tlim, the extent of peripheral fatigue is highly domain-specific, whereas the extent of central fatigue is not. Sensations such as fatigue, pain, and dyspnea may integrate with mechanisms of sense of effort to determine task failure in a manner specific to each intensity domain.NEW & NOTEWORTHY Together with other physiological responses, the neuromuscular fatigue mechanisms, and related perceptual responses, accompanying task failure are suggested to be dependent on the intensity domain within which exercise is sustained. Here, we show that peripheral fatigue demonstrates a high domain specificity, whereas such specificity is absent for central fatigue. Sensations of fatigue, pain, and breathlessness demonstrated intensity domain specificity and might have contributed to reaching maximal levels of RPE and, thus, task failure.

A Narrative Review of Current Concerns and Future Perspectives of the Carbohydrate Mouth Rinse Effects on Exercise Performance.

Previous systematic reviews have confirmed that carbohydrate (CHO) mouth rinse may boost physical exercise performance, despite some methodological aspects likely affecting its ergogenic effect. In this review, we discussed if the exercise mode, pre-exercise fasting status, CHO solutions concentration, CHO solutions temperature, mouth rinse duration, and CHO placebo effects may potentially reduce the CHO mouth rinse ergogenic effect, suggesting possible solutions to manage these potential confounders. The effectiveness of CHO mouth rinse as a performance booster is apparently related to the origin of the exercise-induced neuromuscular fatigue, as CHO mouth rinse unequivocally potentiates endurance rather than sprint and strength exercises performance. Furthermore, ergogenic effects have been greater in fasting than fed state, somehow explaining the varied magnitude of the CHO mouth rinse effects in exercise performance. In this regard, the CHO solution concentration and temperature, as well as the mouth rinse duration, may have increased the variability observed in CHO mouth rinse effects in fasting and fed state. Finally, placebo effects have challenged the potential of the CHO mouth rinse as an ergogenic aid. Therefore, we suggest that future studies should consider methodological controls such as sample size and sample homogeneity, proper familiarization with experimental procedures, and the use of alternative placebo designs to provide unbiased evidence regarding the potential of the CHO mouth rinse as an ergogenic aid.