An Innovative Ergometer to Measure Neuromuscular Fatigue Immediately after Cycling

Reliability of transcranial magnetic stimulation-evoked responses on knee extensor muscles during cycling

Transcranial magnetic stimulation (TMS) measures the excitability and inhibition of corticomotor networks. Despite its task-specificity, few studies have used TMS during dynamic movements and the reliability of TMS paired pulses has not been assessed during cycling. This study aimed to evaluate the reliability of motor evoked potentials (MEP) and short- and long-interval intracortical inhibition (SICI and LICI) on vastus lateralis and rectus femoris muscle activity during a fatiguing single-leg cycling task. Nine healthy adults (2 female) performed two identical sessions of counterweighted single-leg cycling at 60% peak power output until failure. Five single pulses and ten paired pulses were delivered to the motor cortex, and two maximal femoral nerve stimulations (Mmax) were administered during two baseline cycling bouts (unfatigued) and every 5 min throughout cycling (fatigued). When comparing both baseline bouts within the same session, MEP·Mmax-1 and LICI (both ICC: >0.9) were rated excellent while SICI was rated good (ICC: 0.7-0.9). At baseline, between sessions, in the vastus lateralis, Mmax (ICC: >0.9) and MEP·Mmax-1 (ICC: 0.7) demonstrated good reliability; LICI was moderate (ICC: 0.5), and SICI was poor (ICC: 0.3). Across the fatiguing task, Mmax demonstrated excellent reliability (ICC > 0.8), MEP·Mmax-1 ranged good to excellent (ICC: 0.7-0.9), LICI was moderate to excellent (ICC: 0.5-0.9), and SICI remained poorly reliable (ICC: 0.3-0.6). These results corroborate the cruciality of retaining mode-specific testing measurements and suggest that during cycling, Mmax, MEP·Mmax-1, and LICI measures are reliable whereas SICI, although less reliable across days, can be reliable within the same session.

The 1-min sit-to-stand test induces a significant and reliable level of neuromuscular fatigability: insights from a mobile app analysis

PURPOSE

The performance metric associated with the execution of the 1-min sit-to-stand (1STS) typically relies on the number repetitions completed in 1 min. This parameter presents certain limitations (e.g., ceiling effect, motivational factors) which can impede its interpretation. Introducing additional parameters, such as neuromuscular fatigability level, could enhance the informative value of the 1STS and facilitate its interpretation. This study aimed to assess (i) whether the 1STS induces fatigability and (ii) the reliability of the fatigability level.

METHODS

Forty young, healthy, and active participants underwent the 1STS twice during the same session. Isolated sit-to-stand maneuvers were performed before, immediately, and 1 min after completing the 1STS. A mobile app was utilized to obtain time (STST), velocity (STSV), and muscle power (STSP) from these sit-to-stand maneuvers. The pre-post change in these parameters served as the fatigability marker. Reliability was assessed using the intra-class correlation coefficient (ICC) and the coefficient of variation (CV).

RESULTS

The mean number of repetitions during the 1STS was 63 ± 9. Significant decline in performance was observed for STST (13 ± 8%), STSV (-11.2 ± 6%), and STSP (-5.2 ± 3%), with more than 74% of participants exhibiting a decline beyond the minimal detectable change. Excellent between-session reliability (ICC ≥ 0.9; CV ≤ 5.3) was observed for the mobile app variables.

CONCLUSION

The 1STS induces significant levels of fatigability. The fatigability indicators derived from the mobile app demonstrated remarkable reliability. Utilizing this user-friendly interface for computing fatigability may empower professionals to acquire insightful complementary indicators from the 1STS.

Performance and perceived fatigability across the intensity spectrum: role of muscle mass during cycling

The role of muscle mass in modulating performance and perceived fatigability across the entire intensity spectrum during cycling remains unexplored. We hypothesized that at task failure (Tlim), muscle contractile function would decline more following single- (SL) versus double-leg (DL) cycling within severe and extreme intensities, but not moderate and heavy intensities. After DL and SL ramp-incremental tests, on separate days, 11 recreationally active males (V̇o2max: 49.5 ± 7.7 mL·kg-1·min-1) completed SL and DL cycling until Tlim within each intensity domain. Power output for SL trials was set at 60% of the corresponding DL trial. Before and immediately after Tlim, participants performed an isometric maximal voluntary contraction (MVC) coupled with one superimposed and three resting femoral nerve stimulations [100 Hz; 10 Hz; single twitch (Qtw)] to measure performance fatigability. Perceived fatigue, leg pain, dyspnea, and effort were collected during trials. Tlim within each intensity domain was not different between SL and DL (all P > 0.05). MVC declined more for SL versus DL following heavy- (-42 ± 16% vs. -30 ± 18%; P = 0.011) and severe-intensity cycling (-41 ± 12% vs. -31 ± 15%; P = 0.036). Similarly, peak Qtw force declined more for SL following heavy- (-31 ± 12% vs. -22 ± 10%; P = 0.007) and severe-intensity cycling (-49 ± 13% vs. -40 ± 7%; P = 0.048). Except for heavy intensity, voluntary activation reductions were similar between modes. Similarly, except for dyspnea, which was lower for SL versus DL across all domains, ratings of fatigue, pain, and effort were similar at Tlim between exercise modes. Thus, the amount of muscle mass modulates the extent of contractile function impairment in an intensity-dependent manner.NEW & NOTEWORTHY We investigated the modulatory role of muscle mass on performance and perceived fatigability across the entire intensity spectrum. Despite similar time-to-task failure, single-leg cycling resulted in greater impairments in muscle contractile function within the heavy- and severe-intensity domains, but not the moderate- and extreme-intensity domains. Perceived fatigue, pain, and effort were similar between cycling modes. This indicates that the modulatory role of muscle mass on the extent of performance fatigability is intensity domain-dependent.

Acute performance fatigability following continuous versus intermittent cycling protocols is not proportional to total work done

Classical training theory postulates that performance fatigability following a training session should be proportional to the total work done (TWD); however, this notion has been questioned. This study investigated indices of performance and perceived fatigability after primary sessions of high-intensity interval training (HIIT) and constant work rate (CWR) cycling, each followed by a cycling time-to-task failure (TTF) bout. On separate days, 16 participants completed an incremental cycling test, and, in a randomized order, (i) a TTF trial at 80% of peak power output (PPO), (ii) an HIIT session, and (iii) a CWR session, both of which were immediately followed by a TTF trial at 80% PPO. Central and peripheral aspects of performance fatigability were measured using interpolated twitch technique, and perceptual measures were assessed prior to and following the HIIT and CWR trials, and again following the TTF trial. Despite TWD being less following HIIT (P = 0.029), subsequent TTF trial was an average of 125 s shorter following HIIT versus CWR (P < 0.001), and this was accompanied by greater impairments in voluntary and electrically evoked forces (P < 0.001), as well as exacerbated perceptual measures (P < 0.001); however, there were no differences in any fatigue measure following the TTF trial (P ≥ 0.149). There were strong correlations between the decline in TTF and indices of peripheral (r = 0.70) and perceived fatigability (r ≥ 0.80) measured at the end of HIIT and CWR. These results underscore the dissociation between TWD and performance fatigability and highlight the importance of peripheral components of fatigability in limiting endurance performance during high-intensity cycling exercise.

Mathematical modeling of exercise fatigability in the severe domain: A unifying integrative framework in isokinetic condition

Muscle fatigue is the decay in the ability of muscles to generate force, and results from neural and metabolic perturbations. This article presents an integrative mathematical model that describes the decrease in maximal force capacity (i.e. fatigue) over exercises performed at intensities above the critical force Fc (i.e. severe domain). The model unifies the previous Critical Power Model and All-Out Model and can be applied to any exercise described by a changing force F over time. The assumptions of the model are (i) isokinetic conditions, an intensity domain of Fc Collapse

Key Words

• All-out
• Anaerobic capacities
• Critical power
• Endurance
• Exercise fatigability
• Fatigue
• Maximal force capacity
• Muscular capacities
• Power-time relationship
• Time to exhaustion

Collapse

MESH Headings

• Exercise/physiology
• Muscle Fatigue
• Muscles/physiology
• Models, Theoretical
• Muscle, Skeletal/physiology

Collapse

Grants Collapse

Affiliation(s)

M Bowen Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France.
P Samozino Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France
M Vonderscher Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France
D Dutykh Mathematics Department, Khalifa University of Science and Technology, PO Box 127788, Abu Dhabi, United Arab Emirates; Causal Dynamics Pty Ltd, WA 6009, Perth, Australia
B Morel Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France

Collapse

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.

A Comprehensive Evaluation of Multiple Sclerosis-Related Fatigue with a Special Focus on Fatigability

INTRODUCTION

Fatigue is the most common and disabling symptom in multiple sclerosis (MS), being reported by 55% to 78% of patients with MS (PwMS). Etiology of MS-related fatigue remains poorly understood, but an increased neuromuscular fatigability (i.e., greater loss of torque during exercise) could contribute to this phenomenon. This study aimed to characterize the correlates of MS-related fatigue in PwMS using a comprehensive group of physiological and psychosocial measures, with a particular focus on fatigability.

METHODS

Forty-two relapsing-remitting PwMS and 20 healthy subjects were recruited. PwMS were assigned in two groups (high (HF) and low (LF) fatigue) based on two fatigue questionnaires (Fatigue Severity Scale and Modified Fatigue Impact Scale). The main outcomes of this study are derived from incremental cycling completed to task failure (i.e., inability to pedal around 60 rpm). Maximal voluntary contraction (MVC), rating of perceived exertion, and central and peripheral parameters measured using transcranial magnetic and peripheral nerve stimulation were assessed in the knee extensor muscles before, during, and after the fatiguing task. Other potential correlates of fatigue were also tested.

RESULTS

MVC torque decreased to a greater extent for the HF group than LF group after the third common stage of the incremental fatiguing exercise (-15.7% ± 6.6% vs -5.9% ± 13.0%, P < 0.05), and this occurred concurrently with a higher rating of perceived exertion for HF (11.8 ± 2.5 vs 9.3 ± 2.6, P < 0.05). Subjective parameters (depression, quality of life) were worse for HF compared with LF and healthy subjects ( P < 0.001). Moreover, MVC torque loss at the final common stage and maximal heart rate explained 29% of the variance of the Modified Fatigue Impact Scale.

CONCLUSIONS

These results provide novel insight into the relationship between MS-related fatigue and fatigability among PwMS. The HF group exhibited greater performance fatigability, likely contributing to a higher perceived exertion than the LF group when measured during a dynamic task.

Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males

OBJECTIVES

To investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate.

DESIGN

Repeated measures.

METHODS

On separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise.

RESULTS

Compared to sea-level (101 ± 22 W), there was a stepwise reduction in power output with increasing hypoxia severity (-17.9 ± 8.9 %, -27.1 ± 10.7 %, -34.2 ± 12.0 % and - 44.6 ± 15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (-14.5 ± 9.0 %, p < 0.05), independent of condition.

CONCLUSIONS

Increasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.

Intermittent blood flow occlusion modulates neuromuscular, perceptual, and cardiorespiratory determinants of exercise tolerance during cycling

PURPOSE

Constant blood flow occlusion (BFO) superimposed on aerobic exercise can impair muscle function and exercise tolerance; however, no study has investigated the effect of intermittent BFO on the associated responses. Fourteen participants (n = 7 females) were recruited to compare neuromuscular, perceptual, and cardiorespiratory responses to shorter (5:15s, occlusion-to-release) and longer (10:30s) BFO applied during cycling to task failure.

METHODS

In randomized order, participants cycled to task failure (task failure 1) at 70% of peak power output with (i) shorter BFO, (ii) longer BFO, and (iii) no BFO (Control). Upon task failure in the BFO conditions, BFO was removed, and participants continued cycling until a second task failure (task failure 2). Maximum voluntary isometric knee contractions (MVC) and femoral nerve stimuli were performed along with perceptual measures at baseline, task failure 1, and task failure 2. Cardiorespiratory measures were recorded continuously across the exercises.

RESULTS

Task failure 1 was longer in Control than 5:15s and 10:30s (P < 0.001), with no differences between the BFO conditions. At task failure 1, 10:30s elicited a greater decline in twitch force compared to 5:15s and Control (P < 0.001). At task failure 2, twitch force remained lower in 10:30s than Control (P = 0.002). Low-frequency fatigue developed to a greater extent in 10:30s compared to Control and 5:15s (P < 0.047). Dyspnea and Fatigue were greater for Control than 5:15s and 10:30s at the end of task failure 1 (P < 0.002).

CONCLUSION

Exercise tolerance during BFO is primarily dictated by the decline in muscle contractility and accelerated development of effort and pain.

Age-Related Differences between Old and Very Old Men in Performance and Fatigability Are Evident after Cycling but Not Isometric or Concentric Single-Limb Tasks

PURPOSE

This study aimed to compare performance and fatigability between young (n = 13; 18-30 yr), old (n = 13; 60-80 yr), and very old (n = 12; >80 yr) men during a single-joint isometric (ISO) and concentric (CON) task performed on an isokinetic dynamometer and a cycling (BIKE) task.

METHODS

Participants randomly performed incremental tasks consisting of stages of 75 contractions (i.e., 120 s, 0.8 s on/0.8 s off) for ISO and CON and 120 s at 37.5 rpm (similar duty cycle) for BIKE. Increments were set as a percentage of body weight. Knee extensor maximal force, voluntary activation, and twitch amplitude were measured at baseline, after each stage, and at task failure (five out of eight contractions below the target force or 6 s in a row at a cadence <37.5 rpm).

RESULTS

Compared with young men, performance (number of stages) was 24% and 40% lower in old and very old men in ISO, 54% and 59% lower in CON, and 36% and 60% lower in BIKE (all P < 0.05). Performance of old and very old differed only in BIKE (P < 0.01). For the last common stages performed, compared with young, force loss was greater for very old men in ISO and for old and very old men in BIKE (all P < 0.05). Overall, for the last common stage performed and task failure, old and very old men presented similar force loss, alterations in voluntary activation, and twitch amplitude.

CONCLUSIONS

Our findings reveal that, with workloads relative to body weight, differences in performance between old and very old men could only be observed during BIKE (i.e., the more ecologically valid task). Results from isometric or concentric conditions might not be transferable to dynamic exercise with large muscle masses.

Shorter High-Intensity Cycling Intervals Reduce Performance and Perceived Fatigability at Work-Matched but Not Task Failure

INTRODUCTION

The intensity, duration, and distribution of work and recovery phases during high-intensity interval training (HIIT) modulate metabolic perturbations during exercise and subsequently influence the development of performance fatigability and exercise tolerance. This study aimed to characterize neuromuscular, perceptual, and cardiorespiratory responses to work-to-rest ratio-matched HIIT protocols differing in work and rest interval duration.

METHODS

Twelve healthy individuals (six women) first completed a ramp incremental test to determine 90% of peak power output, and then in three randomized visits, they completed three cycling protocols to task failure at 90% of peak power output: (i) 3- to 3-min work-to-passive rest ratio HIIT (HIIT 3min ), (ii) 1- to 1-min work-to-passive rest ratio HIIT (HIIT 1min ), and (iii) constant load (CL). Interpolated twitch technique, including maximal voluntary isometric knee extensions and femoral nerve electrical stimuli, was performed at baseline, every 6 min of work, and task failure. Perceptual and cardiorespiratory responses were recorded every 3 min and continuously across the exercises, respectively.

RESULTS

The work completed during HIIT 1min (8447 ± 5124 kJ) was considerably greater than HIIT 3min (1930 ± 712 kJ) and CL (1076 ± 356) ( P < 0.001). At work-matched, HIIT 1min resulted in a lesser decline in maximal voluntary contraction and twitch force compared with HIIT 3min and CL ( P < 0.001). Perceived effort, pain, and dyspnea were least in HIIT 1min and HIIT 3min compared with CL ( P < 0.001). At task failure, HIIT 1min resulted in less voluntary activation than HIIT 3min ( P = 0.010) and CL ( P = 0.043), and engendered less twitch force decline than CL ( P = 0.021).

CONCLUSIONS

Overall, the mitigated physiological and perceptual responses during shorter work periods (HIIT 1min ) enhance exercise tolerance in comparison to longer work intervals at the same intensity (HIIT 3min , CL).

Blood flow restriction during high-intensity interval cycling exacerbates psychophysiological responses to a greater extent in females than males

This study aimed to characterize neuromuscular, perceptual, and cardiorespiratory responses to high-intensity interval training (HIIT) with superimposed blood flow restriction in males and females. Twenty-four, healthy individuals (n = 12 females) completed two cycling HIIT protocols to task failure (1-min work phases at 90% of peak power output interspersed by 1-min rest phases). The blood flow restriction (BFR) and control (CON) protocols were identical except for the presence and absence of BFR during rest phases, respectively. The interpolated twitch technique, including maximal voluntary isometric knee extension (MVC) and femoral nerve electrical stimuli, was performed at baseline, every six intervals, and task failure. Perceptual and cardiorespiratory responses were recorded every three intervals and continuously during exercise, respectively. Bayesian inference was used to obtain the joint posterior distribution for all parameters and evidence of an effect was determined via the marginal posterior probability (PP). The BFR shortened task duration by 57.3% compared with CON (PP > 0.99), without a sex difference. The application of BFR exacerbated the rate of decline in neuromuscular measures (MVC and twitch force output), increase of perceptual responses (perceived effort, pain, dyspnea, fatigue), and development of cardiorespiratory parameters (minute ventilation and heart rate), compared with CON (PP > 0.95). In addition, BFR exacerbated the neuromuscular, perceptual, and cardiorespiratory responses to a greater extent in females than males (PP > 0.99). Our results suggest that superimposition of blood flow restriction exacerbates psychophysiological responses to a HIIT protocol to a greater extent in females than males.NEW & NOTEWORTHY To our knowledge, no study has explored sex differences in the neuromuscular, perceptual, and cardiorespiratory indices characterizing exercise tolerance during high-intensity interval training (HIIT) with blood flow restriction (BFR) applied only during rest periods. Our results suggest that BFR elicited a decline in exercise performance that could be attributed to integration of psychophysiological responses. However, this integration was sex-dependent where females demonstrated an exacerbated rate of change in these responses compared with males.

Measuring objective fatigability and autonomic dysfunction in clinical populations: How and why?

Fatigue is a major symptom in many diseases, often among the most common and severe ones and may last for an extremely long period. Chronic fatigue impacts quality of life, reduces the capacity to perform activities of daily living, and has socioeconomical consequences such as impairing return to work. Despite the high prevalence and deleterious consequences of fatigue, little is known about its etiology. Numerous causes have been proposed to explain chronic fatigue. They encompass psychosocial and behavioral aspects (e.g., sleep disorders) and biological (e.g., inflammation), hematological (e.g., anemia) as well as physiological origins. Among the potential causes of chronic fatigue is the role of altered acute fatigue resistance, i.e. an increased fatigability for a given exercise, that is related to physical deconditioning. For instance, we and others have recently evidenced that relationships between chronic fatigue and increased objective fatigability, defined as an abnormal deterioration of functional capacity (maximal force or power), provided objective fatigability is appropriately measured. Indeed, in most studies in the field of chronic diseases, objective fatigability is measured during single-joint, isometric exercises. While those studies are valuable from a fundamental science point of view, they do not allow to test the patients in ecological situations when the purpose is to search for a link with chronic fatigue. As a complementary measure to the evaluation of neuromuscular function (i.e., fatigability), studying the dysfunction of the autonomic nervous system (ANS) is also of great interest in the context of fatigue. The challenge of evaluating objective fatigability and ANS dysfunction appropriately (i.e.,. how?) will be discussed in the first part of the present article. New tools recently developed to measure objective fatigability and muscle function will be presented. In the second part of the paper, we will discuss the interest of measuring objective fatigability and ANS (i.e. why?). Despite the beneficial effects of physical activity in attenuating chronic fatigue have been demonstrated, a better evaluation of fatigue etiology will allow to personalize the training intervention. We believe this is key in order to account for the complex, multifactorial nature of chronic fatigue.

Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males

PURPOSE

This study aimed to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF).

METHODS

Ten females and 11 males were evaluated in eight visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; and 4-8) cycling to TTF at PO relative to the MLSS of (i) -15%, (ii) -10 W, (iii) at MLSS, and (iv) +10 W, and (v) +15%. Performance fatigability was characterized by femoral nerve electrical stimulation of knee extensors at baseline; minutes 5, 10, 20, and 30; and TTF. Oxygen uptake, blood lactate concentration, muscle oxygen saturation, and perceived exertion were evaluated.

RESULTS

Approximately 75% of the total performance fatigability occurred within 5 min of exercise, independently of exercise intensity, followed by a further change at minute 30. Contractile function declined more in males than females (all P < 0.05). At task failure, exercise duration declined from MLSS -15% to MLSS +15% (all P < 0.05), accompanied by a greater rate of decline after MLSS +15% and MLSS +10 compared with MLSS, MLSS -10 , and MLSS -15% for voluntary activation (-0.005 and -0.003 vs -0.002, -0.001 and -0.001%·min -1 , respectively) and contractile function (potentiated single twitch force, -0.013 and -0.009 vs -0.006, -0.004 and -0.004%·min -1 , respectively).

CONCLUSIONS

Whereas the time course of performance fatigability responses was similar regardless of exercise intensity and sex, the total amplitude and rate of change were affected by the distinct metabolic disturbances around the MLSS, leading to different performance fatigability etiologies at task failure.

Age-related performance fatigability: a comprehensive review of dynamic tasks

Adult ageing is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability of isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared to static contractions. This review provides a comprehensive summary of age-related fatigability in dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks which constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability of old compared to young adults. These unconstrained velocity tasks, that are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability of dynamic tasks should be evaluated using task-specific contractions (i.e., dynamic), particularly for assessment of spinal and supra-spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.

Mechanisms of Neuromuscular Fatigability in People with Cancer-Related Fatigue

INTRODUCTION

Cancer-related fatigue (CRF) is a debilitating symptom that affects around one-third of people for months or years after cancer treatment. In a recent study, we found that people with posttreatment CRF have greater neuromuscular fatigability. The aim of this secondary analysis was to examine the etiology of neuromuscular fatigability in people with posttreatment CRF.

METHODS

Ninety-six people who had completed cancer treatment were dichotomized into two groups (fatigued and nonfatigued) based on a clinical cut point for fatigue. Alterations in neuromuscular function (maximal voluntary contraction peak force, voluntary activation, potentiated twitch force, and EMG) in the knee extensors were assessed across three common stages of an incremental cycling test. Power outputs during the fatigability test were expressed relative to gas exchange thresholds to assess relative exercise intensity.

RESULTS

The fatigued group had a more pronounced reduction in maximal voluntary contraction peak force and potentiated twitch force throughout the common stages of the incremental cycling test (main effect of group: P < 0.001, ηp2 = 0.18 and P = 0.029, ηp2 = 0.06, respectively). EMG was higher during cycling in the fatigued group (main effect of group: P = 0.022, ηp2 = 0.07). Although the relative intensity of cycling was higher in the fatigued group at the final common stage of cycling, this was not the case during the initial two stages, despite the greater impairments in neuromuscular function.

CONCLUSIONS

Our results suggest that the rapid impairments in neuromuscular fatigability in people with CRF were primarily due to disturbances at the level of the muscle rather than the central nervous system. This could affect the ability to tolerate daily physical activities.

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, eleven young males performed four constant-power output trials to the limit of tolerance (T_lim) at four distinct domain-specific workloads. These trials were preceded and followed by 5-s knee-extension maximal voluntary contractions (MVC) and femoral nerve electrical stimuli to quantify peripheral and central fatigue. Additionally, perceptual measures including ratings of global fatigue, legs pain, dyspnea and perceived effort (RPE) were also collected. At T_lim, 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 T_lim, subjective ratings of global fatigue were progressively higher with lower exercise intensities, while 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 T_lim 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.

Disparate Mechanisms of Fatigability in Response to Prolonged Running versus Cycling of Matched Intensity and Duration

INTRODUCTION

Running and cycling represent two of the most common forms of endurance exercise. However, a direct comparison of the neuromuscular consequences of these two modalities after prolonged exercise has never been made. The aim of this study was to compare the alterations in neuromuscular function induced by matched-intensity and duration cycling and running exercise.

METHODS

During separate visits, 17 endurance-trained male participants performed 3 h of cycling and running at 105% of the gas exchange threshold. Neuromuscular assessments were taken are preexercise, midexercise, and postexercise, including knee extensor maximal voluntary contractions (MVC), voluntary activation (VA), high- and low-frequency doublets (Db100 and Db10, respectively), potentiated twitches (Qtw,pot), motor evoked potentials (MEP), and thoracic motor evoked potentials (TMEP).

RESULTS

After exercise, MVC was similarly reduced by ~25% after both running and cycling. However, reductions in VA were greater after running (-16% ± 10%) than cycling (-10% ± 5%; P < 0.05). Similarly, reductions in TMEP were greater after running (-78% ± 24%) than cycling (-15% ± 60%; P = 0.01). In contrast, reductions in Db100 (running vs cycling, -6% ± 21% vs -13% ± 6%) and Db10:100 (running vs cycling, -6% ± 16% vs -19% ± 13%) were greater for cycling than running (P ≤ 0.04).

CONCLUSIONS

Despite similar decrements in the knee extensor MVC after running and cycling, the mechanisms responsible for force loss differed. Running-based endurance exercise is associated with greater impairments in nervous system function, particularly at the spinal level, whereas cycling-based exercise elicits greater impairments in contractile function. Differences in the mechanical and metabolic demands imposed on the quadriceps could explain the disparate mechanisms of neuromuscular impairment after these two exercise modalities.

Neuromuscular fatigability during repeated sprints assessed with an innovative cycle ergometer

PURPOSE

Repeated sprint ability is an integral component of team sports. This study aimed to evaluate fatigability development and its aetiology during and immediately after a cycle repeated sprint exercise performed until a given fatigability threshold.

METHODS

On an innovative cycle ergometer, 16 healthy males completed an RSE (10-s sprint/28-s recovery) until task failure (TF): a 30% decrease in sprint mean power (Pmean). Isometric maximum voluntary contraction of the quadriceps (IMVC), central alterations [voluntary activation (VA)], and peripheral alterations [twitch (Pt)] were evaluated before (pre), immediately after each sprint (post), at TF and 3 min after. Sprints were expressed as a percentage of the total number of sprints to TF (TS_TF). Individual data were extrapolated at 20, 40, 60, and 80% TS_TF.

RESULTS

Participants completed 9.7 ± 4.2 sprints before reaching a 30% decrease in Pmean. Post-sprint IMVCs were decreased from pre to 60% TS_TF and then plateaued (pre: 345 ± 56 N, 60% 247 ± 55 N, TF: 233 ± 57 N, p < 0.001). Pt decreased from 20% and plateaued after 40% TS_TF (p < 0.001, pre-TF = - 45 ± 13%). VA was not significantly affected by repeated sprints until 60% TS_TF (pre-TF = - 6.5 ± 8.2%, p = 0.036). Unlike peripheral parameters, VA recovered within 3 min (p = 0.042).

CONCLUSION

During an RSE, Pmean and IMVC decreases were first concomitant to peripheral alterations up to 40% TS_TF and central alterations was only observed in the second part of the test, while peripheral alterations plateaued. The distinct recovery kinetics in central versus peripheral components of fatigability further confirm the necessity to reduce traditional delays in neuromuscular fatigue assessment post-exercise.

The effects of pain induced by blood flow occlusion in one leg on exercise tolerance and corticospinal excitability and inhibition of the contralateral leg in males

Experiencing pain in one leg can alter exercise tolerance and neuromuscular fatigue (NMF) responses in the contralateral leg; however, the corticospinal modulations to non-local experimental pain induced by blood flow occlusion remain unknown. In three randomized visits, thirteen male participants performed 25% of isometric maximal voluntary contraction (25%IMVC) to task failure with one leg preceded by (i) 6-min rest (CON), (ii) cycling at 80% of peak power output until task failure with the contralateral leg (CYCL) or (iii) CYCL followed by blood flow occlusion (OCCL) during 25%IMVC. NMF assessments (IMVC, voluntary activation [VA] and potentiated twitch [Qtw]) were performed at baseline and task failure. During the 25%IMVC, transcranial magnetic stimulations were performed to obtain motor evoked potential (MEP), silent period (SP), and short intracortical inhibition (SICI). 25%IMVC was shortest in OCCL (105±50s) and shorter in CYCL (154±68s) than CON (219±105s) (P<0.05). IMVC declined less after OCCL (-24±19%) and CYCL (-27±18%) then CON (-35±11%) (P<0.05). Qtw declined less in OCCL (-40±25%) compared to CYCL (-50±22%) and CON (-50±21%) (P<0.05). VA was similar amongst conditions. MEP and SP increased and SICI decreased throughout the task while SP was longer for OCCL compared to CYC condition (P<0.05). The results suggest that pain in one leg diminishes contralateral limb exercise tolerance and NMF development and modulate corticospinal inhibition in males. Novelty: Pain in one leg diminished MVC and twitch force decline in the contralateral limb Experimental pain induced by blood flow occlusion may modulation corticospinal inhibition of the neural circuitries innervating the contralateral exercise limb.

Comparing muscle VO2 from near-infrared spectroscopy desaturation rate to pulmonary VO2 during cycling below, at and above the maximal lactate steady state

Muscle oxygen uptake (V̇O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O_2m. However, its correspondence with pulmonary oxygen uptake (V̇O_2p) during exercise remains unknown.

PURPOSE

to investigate the V̇O_2m and V̇O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

METHODS

Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2-3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4-6) constant-PO exercise bouts to task failure at (i) 15% below MLSS (MLSS_-15%); (ii) MLSS; (iii) 15% above MLSS (MLSS_+15%). V̇O_2m was estimated at baseline, at min 5, 10, 20, 30, and at task failure. V̇O_2p was continuously recorded during the constant-PO bouts.

RESULTS

V̇O_2pand V̇O_2m significantly increased from min 5 to min 30 in MLSS condition (all p < 0.05) and from min 5 to min 10 in MLSS_+15% condition (all p < 0.05). V̇O_2pand V̇O_2m were correlated (r² adj range of 0.70-0.98, all p < 0.001) amongst exercise intensities in both females and males. Additionally, both variables were also correlated when expressed as percent (r² adj range of 0.52-0.77, all p < 0.001).

CONCLUSION

V̇O_2p and V̇O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇O_2p andV̇O_2m were correlated regardless the exercise intensity and sex of the participants.

The effects of exercise intensity and duration on the relationship between the slow component of V̇O2 and peripheral fatigue

AIM

If the development of the oxygen uptake slow component (V̇O_2SC ) and muscle fatigue are related, these variables should remain coupled in a time- and intensity-dependent manner.

METHODS

16 participants (7 females) visited the laboratory on 7 separate occasions: (1) three 6-minutes moderate-intensity cycling exercise bouts proceeded by a ramp incremental test; (2-3) 30-minutes constant power output (PO) exercise bout to determine the maximal lactate steady state (MLSS); (4-7) constant-PO exercise bouts to task failure (TTF), pseudorandomized order, at (i) 15% below the PO at MLSS; (ii) 10 W below MLSS; (iii) MLSS; (iv) 10 W above MLSS (first intensity and randomized order thereafter). Neuromuscular fatigue was characterized by isometric maximal voluntary contractions and femoral nerve electrical stimulation of knee extensors to measure peripheral fatigue at baseline, at min 5, 10, 20, 30 and TTF. Pulmonary oxygen uptake (V̇O₂ ) was continuously recorded during the constant-PO bouts and V̇O_2SC was characterized based on each individual V̇O₂ kinetics during moderate transitions.

RESULTS

The development of V̇O_2SC and peripheral fatigue were correlated across time (r² adj range of 0.64-0.80) and amongst each exercise intensity (r² adj range of 0.26-0.30) (all P < .001). Also, TTF was correlated with V̇O_2SC and neuromuscular fatigue parameters (r² adj range of 0.52-0.82, all P < .001).

CONCLUSION

The V̇O_2SC and peripheral fatigue development are correlated throughout the exercise in a time- and intensity-dependent manner, suggesting that the V̇O_2SC may depend on muscle fatigue even if the mechanisms of reduced contractile function are different amongst intensities.

The Exercising Brain: An Overlooked Factor Limiting the Tolerance to Physical Exertion in Major Cardiorespiratory Diseases?

“Exercise starts and ends in the brain”: this was the title of a review article authored by Dr. Bengt Kayser back in 2003. In this piece of work, the author highlights that pioneer studies have primarily focused on the cardiorespiratory-muscle axis to set the human limits to whole-body exercise tolerance. In some circumstances, however, exercise cessation may not be solely attributable to these players: the central nervous system is thought to hold a relevant role as the ultimate site of exercise termination. In fact, there has been a growing interest relative to the “brain” response to exercise in chronic cardiorespiratory diseases, and its potential implication in limiting the tolerance to physical exertion in patients. To reach these overarching goals, non-invasive techniques, such as near-infrared spectroscopy and transcranial magnetic stimulation, have been successfully applied to get insights into the underlying mechanisms of exercise limitation in clinical populations. This review provides an up-to-date outline of the rationale for the “brain” as the organ limiting the tolerance to physical exertion in patients with cardiorespiratory diseases. We first outline some key methodological aspects of neuromuscular function and cerebral hemodynamics assessment in response to different exercise paradigms. We then review the most prominent studies, which explored the influence of major cardiorespiratory diseases on these outcomes. After a balanced summary of existing evidence, we finalize by detailing the rationale for investigating the “brain” contribution to exercise limitation in hitherto unexplored cardiorespiratory diseases, an endeavor that might lead to innovative lines of applied physiological research.

Physiological and psychosocial correlates of cancer-related fatigue

PURPOSE

Cancer-related fatigue (CRF) is a common and distressing symptom of cancer that may persist for years following treatment completion. However, little is known about the pathophysiology of CRF. Using a comprehensive group of gold-standard physiological and psychosocial assessments, this study aimed to identify correlates of CRF in a heterogenous group of cancer survivors.

METHODS

Using a cross-sectional design to determine the physiological and psychosocial correlates of CRF, ninety-three cancer survivors (51 fatigued, 42 non-fatigued) completed assessments of performance fatigability (i.e. the decline in muscle strength during cycling), cardiopulmonary exercise testing, venous blood samples for whole blood cell count and inflammatory markers and body composition. Participants also completed questionnaires measuring demographic, treatment-related, and psychosocial variables.

RESULTS

Performance fatigability, time-to-task-failure, peak oxygen uptake (V̇O_2peak), tumor necrosis factor-α (TNF-α), body fat percentage, and lean mass index were associated with CRF severity. Performance fatigability, V̇O_2peak, TNF-α, and age explained 35% of the variance in CRF severity. Those with clinically-relevant CRF reported more pain, more depressive symptoms, less perceived social support, and were less physically active than non-fatigued cancer survivors.

CONCLUSIONS

The present study utilised a comprehensive group of gold-standard physiological and psychosocial assessments and the results give potential insight into the mechanisms underpinning the association between physical inactivity, physical deconditioning and CRF.

IMPLICATIONS FOR CANCER SURVIVORS

Given the associations between CRF and both physiological and psychosocial measures, this study identifies targets that can be measured by rehabilitation professionals and used to guide tailored interventions to reduce fatigue.

Power Reserve at Intolerance in Ramp-Incremental Exercise Is Dependent on Incrementation Rate

INTRODUCTION

The mechanism(s) of exercise intolerance at V˙O2max remain poorly understood. In health, standard ramp-incremental (RI) exercise is limited by fatigue-induced reductions in maximum voluntary cycling power. Whether neuromuscular fatigue also limits exercise when the RI rate is slow and RI peak power at intolerance is lower than standard RI exercise, is unknown.

METHODS

In twelve healthy participants, maximal voluntary cycling power was measured during a short (~6 s) isokinetic effort at 80 rpm (Piso) at baseline and, using an instantaneous switch from cadence-independent to isokinetic cycling, immediately at the limit of RI exercise with RI rates of 50, 25, and 10 W·min-1 (RI-50, RI-25, and RI-10). Breath-by-breath pulmonary gas exchange was measured throughout.

RESULTS

Baseline Piso was not different among RI rates (analysis of variance; P > 0.05). Tolerable duration increased with decreasing RI rate (RI-50, 411 ± 58 s vs RI-25, 732 ± 93 s vs RI-10, 1531 ± 288 s; P < 0.05). At intolerance, V˙O2peak was not different among RI rates (analysis of variance; P > 0.05), but RI peak power decreased with RI rate (RI-50, 361 ± 48 W vs RI-25, 323 ± 39 W vs RI-10, 275 ± 38 W; P < 0.05). Piso at intolerance was 346 ± 43 W, 353 ± 45 W, and 392 ± 69 W for RI-50, RI-25, and RI-10, respectively (P < 0.05 for RI-10 vs RI-50 and RI-25). At intolerance, in RI-50 and RI-25, Piso was not different from RI peak power (P > 0.05), thus there was no "power reserve." In RI-10, Piso was greater than RI peak power at intolerance (P < 0.001), that is, there was a "power reserve."

CONCLUSIONS

In RI-50 and RI-25, the absence of a power reserve suggests the neuromuscular fatigue-induced reduction in Piso coincided with V˙O2max and limited the exercise. In RI-10, the power reserve suggests neuromuscular fatigue was insufficient to limit the exercise, and additional mechanisms contributed to intolerance at V˙O2max.

Exercising muscle mass influences neuromuscular, cardiorespiratory, and perceptual responses during and following ramp-incremental cycling to task failure

Neuromuscular (NM), cardiorespiratory, and perceptual responses to maximal-graded exercise using different amounts of active muscle mass remain unclear. We hypothesized that during dynamic exercise, peripheral NM fatigue (declined twitch force) and muscle pain would be greater using smaller muscle mass, whereas central fatigue (declined voluntary activation) and ventilatory variables would be greater using larger muscle mass. Twelve males (29.8 ± 4.7 years) performed two ramp-incremental cycling tests until task failure: 1) single-leg (SL) with 10 W·min^-1 ramp and 2) double-leg (DL) with 20 W·min^-1 ramp. NM fatigue was assessed at baseline, task failure (post), and after 1, 4, and 8 min of recovery. Cardiorespiratory and perceptual variables [i.e., ratings of perceived exertion (RPE), pain, and dyspnea] were measured throughout cycling. Exercise duration was similar between sessions (SL: 857.7 ± 263.6 s; DL: 855.0 ± 218.8 s; P = 0.923), and higher absolute peak power output was attained in DL (SL: 163.2 ± 43.8 W; DL: 307.0 ± 72.0 W; P < 0.001). Although central fatigue did not differ between conditions (SL: -6.6 ± 6.5%; DL: -3.5 ± 4.8%; P = 0.091), maximal voluntary contraction (SL: -41.6 ± 10.9%; DL: -33.7 ± 8.5%; P = 0.032) and single twitch forces (SL: -59.4 ± 18.8%; DL: -46.2 ± 16.2%; P = 0.003) declined more following SL. DL elicited higher peak oxygen uptake (SL: 42.1 ± 10.0 mL·kg^-1·min^-1; DL: 50.3 ± 9.3 mL·kg^-1·min^-1; P < 0.001), ventilation (SL: 137.1 ± 38.1 L·min^-1; DL: 171.5 ± 33.2 L·min^-1; P < 0.001), and heart rate (SL: 167 ± 21 bpm; DL: 187 ± 8 bpm; P = 0.005). Dyspnea (P = 0.025) was higher in DL; however, RPE (P = 0.005) and pain (P < 0.001) were higher in SL. These results suggest that interplay between NM, cardiorespiratory, and perceptual determinants of exercise performance during ramp-incremental cycling to task failure is muscle mass dependent.

Slight power output manipulations around the maximal lactate steady state have a similar impact on fatigue in females and males

Neuromuscular fatigue (NMF) and exercise performance are affected by exercise intensity and sex differences. However, whether slight changes in power output (PO) below and above the maximal lactate steady state (MLSS) impact NMF and subsequent performance (time to task failure, TTF) is unknown. This study compared NMF and TTF in females and males in response to exercise performed at MLSS, 10 W below (MLSS_-10) and above (MLSS₊₁₀). Twenty participants (9 females) performed three 30-min constant-PO exercise bouts followed (1-min delay) by a TTF at 80% of the peak-PO. NMF was characterized by isometric maximal voluntary contractions (IMVC) and femoral nerve electrical stimulation of knee extensors [e.g., peak torque of potentiated high-frequency (Db100) and single twitch (TwPt)] before and immediately after the constant-PO and TTF bouts. IMVC declined less after MLSS_-10 (-18 ± 10%) compared to MLSS (-26 ± 14%) and MLSS₊₁₀ (-31 ± 11%; all P < 0.05), and the Db100 decline was greater after MLSS₊₁₀ (-24 ± 14%) compared to the other intensities (MLSS_-10: -15 ± 9%; MLSS: -18 ± 11%; all P < 0.05). Females showed smaller reductions, relative to baseline, in IMVC and TwPt compared to males after constant-PO bouts (all P < 0.05), this difference being not dependent on intensity. TTF was negatively impacted by increasing the PO in the constant-PO (P < 0.001), with no differences in end-exercise NMF (P > 0.05). Slight manipulations in PO around MLSS elicited great changes in the reduction of maximal voluntary force and impairments in contractile function. Although NMF was lower in females compared to males, the changes in PO around the MLSS impacted both sexes similarly.NEW & NOTEWORTHY It is unknown whether minimum changes in power output (PO) below and above the maximal lactate steady state (MLSS) affect neuromuscular fatigue (NMF) development in females and males. The present data showed that a decrease or increase of 10 W in PO in relation to MLSS elicited lower and greater impairments in contractile function, respectively. Even though females had less of an overall decline in NMF than males, similar exercise intensity-dependent response occurred independently of sex.

Distinct pacing profiles result in similar perceptual responses and neuromuscular fatigue development: Why different "roads" finish at the same line?

ABSTRACTThe current study analysed the effect of distinct pacing profiles (i.e. U, J, and inverted J) in the perceptual responses and neuromuscular fatigue (NMF) development following a 4-km cycling time trial (TT). Twenty-one cyclists with similar training status were allocated into three different groups based on their pacing profile spontaneously adopted during TT. Rating of perceived exertion (RPE), oxygen uptake (⩒O₂) and heart rate (HR) were continuously recorded. NMF was assessed by using isometric maximal voluntary contractions (IMVC), while the central [i.e. voluntary activation (VA)] and peripheral fatigue of knee extensors [i.e. peak torque of potentiated twitches (TwPt)] were evaluated using electrically evoked contractions performed pre and 2 min after the TT. TT performance was not different amongst pacing profiles (U = 377 ± 20 s; J = 392 ± 23 s; J-i = 381 ± 20 s) (all P > 0.05). RPE, ⩒O₂ and HR increased similarly throughout the TT regardless the pacing strategy (all P > 0.05). Similarly, IMVC (U = -9.9 ± 8.8; J = -9.6 ± 4.5%; J-i = -13.8 ± 11.3%), VA (U = -2.3 ± 1.7%; J = -5.4 ± 2.2%; J-i = -6.4 ± 4.5%) and TwPt (U = -32.5 ± 12.0%; J = -29.5 ± 8.0%; J-i = -33.6 ± 13.6%) were similar amongst pacing profiles (all P > 0.05). Therefore, endurance athletes with similar training status showed the same perceived responses and NMF development regardless the pacing profile spontaneously adopted. It was suggested that these responses occurred in order to preserve a similar rate of change in systemic responses (i.e. RPE, ⩒O₂ and HR) and NMF development, ultimately resulting in same TT performance.Highlights Different pacing profiles resulted in the same performance in a 4-km cycling time trial.The similar performance might be due to achievement of the same sensory tolerance limit.There was no difference for perceptual, metabolic and neuromuscular fatigue responses.

Quantification of Neuromuscular Fatigue: What Do We Do Wrong and Why?

Neuromuscular fatigue (NMF) is usually assessed non-invasively in healthy, athletic or clinical populations with the combination of voluntary and evoked contractions. Although it might appear relatively straightforward to magnetically or electrically stimulate at different levels (cortical/spinal/muscle) and to measure mechanical and electromyographic responses to quantify neuromuscular adjustments due to sustained/repeated muscle contractions, there are drawbacks that researchers and clinicians need to bear in mind. The aim of this opinion paper is to highlight the pitfalls inevitably faced when NMF is quantified. The first problem might arise from the definition of fatigue itself and the parameter(s) used to measure it; for instance, measuring power vs. isometric torque may lead to different conclusions. Another potential limitation is the delay between exercise termination and the evaluation of neuromuscular function; the possible underestimation of exercise-induced neural and contractile impairment and misinterpretation of fatigue etiology will be discussed, as well as solutions recently proposed to overcome this problem. Quantification of NMF can also be biased (or not feasible) because of the techniques themselves (e.g. results may depend on stimulation intensity for transcranial magnetic stimulation) or the way data are analyzed (e.g. M wave peak-to-peak vs first phase amplitude). When available, alternatives recently suggested in the literature to overcome these pitfalls are considered and recommendations about the best practices to assess NMF (e.g. paying attention to the delay between exercise and testing, adapting the method to the characteristics of the population to be tested and considering the limitations associated with the techniques) are proposed.

Dynamic Changes of Performance Fatigability and Muscular O2 Saturation in a 4-km Cycling Time Trial

PURPOSE

The current study characterized the performance fatigability etiology, immediately after exercise cessation, and its relation to the dynamic changes in muscle O2 saturation (SmO2) at different TT phases.

METHODS

Twelve males performed three separated TT of different distances, in a crossover counterbalanced design, until the end of the fast-start (FS, 827 ± 135 m), even-pace (EP, 3590 ± 66 m), or end-spurt (ES, 4000 m) TT phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVC), whereas the maximal voluntary activation (VA) and contractile function of knee extensors (e.g., peak torque of potentiated twitches [TwPt]) were evaluated using electrically evoked contractions performed before and immediately after each exercise bouts. SmO2, power output (PO), and EMG were also recorded.

RESULTS

Immediately after the FS phase, there were lower values for IMVC (-23%), VA (-8%), and TwPt (-43%) (all P < 0.001), but no further changes were measured after EP (IMVC, -28%; VA, -8%; TwPt, -38%). After the ES phase, IMVC (-34%) and TwPt (-59%) further decreased compared with the previous phases (P < 0.05). There were lower SmO2 and higher EMG/PO values during FS and ES compared with EP phase.

CONCLUSION

FS and EP phases had similar performance fatigability etiology, but ES showed further impairments in contractile function. This later finding might be due to the abrupt changes in SmO2 and EMG/PO because of the high exercise intensity during the ES, which elicited maximal decline in contractile function at the finish line.

Prior Upper Body Exercise Impairs 4-km Cycling Time-Trial Performance Without Altering Neuromuscular Function

Purpose: This study investigated the effects of previous exhaustive upper body exercise on performance and neuromuscular fatigue following a 4-km cycling time-trial (4-km TT). Methods: Eight recreational cyclists performed a 4-km TT with (ARM_PRE) or without (CONTR) a previous arm-crank maximal incremental test. In each experimental session, neuromuscular fatigue was evaluated with a series of electrically evoked and maximal voluntary isometric contractions (MVC). Oxygen uptake ( V ˙ O₂), heart rate, electromyographic muscle activity (EMG_RMS) and rating of perceived exertion (RPE) were also recorded throughout the 4-km TT. Results: The average power output during the 4-km TT was reduced (P = .027) for the ARM_PRE (299 ± 59 W) group, compared with CONTR (310 ± 59 W) and overall performance in 4-km TT was impaired (P = .021) in ARM_PRE (382 ± 28 s) compared with CONTR (376 ± 27 s). The decrease observed in MVC (P = .033) and potentiated peak twitch force (P = .004) at post-TT were similar between the ARM_PRE and CONTR conditions (P = .739 and P = .493, respectively). There was no (P = .619) change in voluntary activation at post-TT between conditions. V ˙ O₂, EMG_RMS and RPE measured throughout the 4-km TT were not significantly different between the conditions (P = .558, P = .558 and P = .940, respectively). The rate of RPE change relative to power output average and heart rate was higher (P = .030 and P = .013, respectively) in ARM_PRE (0.031 ± 0.018 AU/W and 168 ± 8 bpm) than CONTR (0.022 ± 0.010 AU/W and 161 ± 7 bpm). Conclusion: These results suggest that impaired performance in ARM_PRE was mostly due to pronounced perception of effort rather than neuromuscular fatigue.

Neuromuscular responses to fatiguing locomotor exercise

Over the last two decades, an abundance of research has explored the impact of fatiguing locomotor exercise on the neuromuscular system. Neurostimulation techniques have been implemented prior to and following locomotor exercise tasks of a wide variety of intensities, durations, and modes. These techniques have allowed for the assessment of alterations occurring within the central nervous system and the muscle, while techniques such as transcranial magnetic stimulation and spinal electrical stimulation have permitted further segmentalization of locomotor exercise-induced changes along the motor pathway. To this end, the present review provides a comprehensive synopsis of the literature pertaining to neuromuscular responses to locomotor exercise. Sections of the review were divided to discuss neuromuscular responses to maximal, severe, heavy and moderate intensity, high-intensity intermittent exercise, and differences in neuromuscular responses between exercise modalities. During maximal and severe intensity exercise, alterations in neuromuscular function reside primarily within the muscle. Although post-exercise reductions in voluntary activation following maximal and severe intensity exercise are generally modest, several studies have observed alterations occurring at the cortical and/or spinal level. During prolonged heavy and moderate intensity exercise, impairments in contractile function are attenuated with respect to severe intensity exercise, but are still widely observed. While reductions in voluntary activation are greater during heavy and moderate intensity exercise, the specific alterations occurring within the central nervous system remain unclear. Further work utilizing stimulation techniques during exercise and integrating new and emerging techniques such as high-density electromyography is warranted to provide further insight into neuromuscular responses to locomotor exercise.

Time Course of Recovery after Cycling Repeated Sprints

PURPOSE

The present study investigated the recovery of performance and neuromuscular fatigue after cycling repeated sprints.

METHODS

Ten participants performed two sessions of repeated sprints (one session: 10 × 10-s sprints, 30-s recovery) separated by 24 h (R24-S1 and R24-S2) and two sessions separated by 48 h (R48-S1 and R48-S2). The recovery condition (i.e., 24 or 48 h) was randomized and separated by 1 wk. All sessions were performed on a recumbent bike, allowing minimal delay between sprints termination and neuromuscular measurements. Neuromuscular function of knee extensors (neuromuscular assessment [NMA]) was assessed before sessions (presession), after the fifth sprint (midsession), and immediately after (postsession). Before sessions, baseline NMA was also carried out on an isometric chair. The NMA (bike and chair) was composed of maximal voluntary contraction (MVC) of knee extension and peripheral neuromuscular stimulation during the MVC and on relaxed muscle.

RESULTS

The sprints performance was not significantly different between sessions and did not presented significant interaction between recovery conditions. MVC was significantly lower at R24-S2 compared with R24-S1 (-6.5% ± 8.8%, P = 0.038) and R48-S2 (-5.6% ± 8.2%, P = 0.048), whereas resting potentiated high-frequency doublet (Db100) was lower at R24-S2 compared with R24-S1 (-10.4 ± 8.3, P = 0.01) (NMA on chair). There were significant reductions in MVC (>30%, P < 0.001) and Db100 (>38%, P < 0.001) from pre- to postsession in all sessions, without significant interactions between recovery conditions (NMA on bike).

CONCLUSION

Cycling repeated sprints induce significant fatigue, particularly at the peripheral level, which is fully restored after 48 h, but not 24 h, of recovery. One versus two days of recovery does not affect neuromuscular fatigue appearance during cycling repeated-sprint sessions.

Multiple sclerosis-related fatigue: the role of impaired corticospinal responses and heightened exercise fatigability

It is unclear whether motor fatigability and perceived fatigue share a common pathophysiology in people with multiple sclerosis (PwMS). This cross-sectional investigation explored the relationship between the mechanisms of motor fatigability from cycling and fatigue severity in PwMS. Thirteen highly fatigued (HF) and thirteen nonfatigued (LF) PwMS and thirteen healthy controls (CON) completed a step test until volitional exhaustion on an innovative cycle ergometer. Neuromuscular evaluations involving femoral nerve electrical stimulation and transcranial magnetic stimulation were performed every 3 min throughout cycling. One-way ANOVA at baseline and exhaustion uncovered evidence of consistently smaller motor evoked potential (MEP) amplitudes (P = 0.011) and prolonged MEP latencies (P = 0.041) in HF as well as a greater decline in maximal voluntary contraction force (HF: 63 ± 13%; LF: 75 ± 13%; CON: 73 ± 11% of pre; P = 0.037) and potentiated twitch force (HF: 35 ± 13%; LF: 50 ± 16%; CON: 47 ± 17% of pre; P = 0.049) in HF at volitional exhaustion. Hierarchical regression determined that fatigue severity on the Fatigue Severity Scale was predicted by prolonged MEP latencies (change in r² = 0.389), elevated peripheral muscle fatigability (change in r² = 0.183), and depressive symptoms (change in r² = 0.213). These findings indicate that MS-related fatigue is distinguished by disrupted corticospinal responsiveness, which could suggest progressive pathology, but fatigability from whole body exercise and depressive symptoms also influence perceptions of fatigue in PwMS.NEW & NOTEWORTHY The etiology of fatigability from whole body exercise was examined for the first time to accurately elucidate the relationship between fatigue and fatigability in multiple sclerosis (MS). Compromised corticospinal responsiveness predicted fatigue severity, providing a novel, objective indicator of fatigue in MS. Although the impaired corticomotor transmission did not aggravate muscle activation in this group of people with multiple sclerosis (PwMS) of lower disability, heightened muscle fatigability was seen to contribute to perceptions of fatigue in PwMS.

Eccentric exercise and delayed onset muscle soreness reduce the variability of active cervical movements

People with acute neck pain commonly present with restricted neck movement. However, it is unknown whether the presence of acute pain affects the quality of neck movement, specifically neck movement variability. We examined the effects of acute neck muscle soreness induced via eccentric exercise in healthy volunteers, on the variability of neck movement by examining changes in parameters of the helical axis during active neck movements. An experimental, single-arm repeated measures study recruited 32 healthy participants, male and female, aged between 18 and 55 years. Repetitive active neck movements (flexion-extension, bilateral lateral flexion and bilateral rotation) were performed at different speeds, either at full range of motion (RoM) or restricted to 45° RoM at baseline, pre-exercise (T0), immediately following eccentric neck exercise (T1), 24 h (T2) and 48 h post-exercise (T3). The mean distance (MD) and mean angle (MA) parameters of the helical axis were extracted to quantify movement variability. MD, measured during movements performed at full RoM, reduced significantly at T2 compared to T0 (P = 0.001) regardless of direction or speed of movement. MA was significantly lower at T2 and T3 compared to T1 (P = 0.029 and P = 0.033, respectively). When RoM was restricted to 45°, significantly lower MD values were observed at T3 compared to T1 (P = 0.034), and significantly lower MA values were measured at T3 compared to T0, T1 and T2 (all P < 0.0001). This study uniquely demonstrates that neck movement variability is reduced immediately after, 24 h and 48 h after eccentric exercise, indicating that acute neck muscle soreness modifies the quality of neck movement.

Cycling Biomechanics and Its Relationship to Performance

State-of-the-art biomechanical laboratories provide a range of tools that allow precise measurements of kinematic, kinetic, motor and physiologic characteristics. Force sensors, motion capture devices and electromyographic recording measure the forces exerted at the pedal, saddle, and handlebar and the joint torques created by muscle activity. These techniques make it possible to obtain a detailed biomechanical analysis of cycling movements. However, despite the reasonable accuracy of such measures, cycling performance remains difficult to fully explain. There is an increasing demand by professionals and amateurs for various biomechanical assessment services. Most of the difficulties in understanding the link between biomechanics and performance arise because of the constraints imposed by the bicycle, human physiology and musculo-skeletal system. Recent studies have also pointed out the importance of evaluating not only output parameters, such as power output, but also intrinsic factors, such as the cyclist coordination. In this narrative review, we present various techniques allowing the assessment of a cyclist at a biomechanical level, together with elements of interpretation, and we show that it is not easy to determine whether a certain technique is optimal or not.

Greater Short-Time Recovery of Peripheral Fatigue After Short- Compared With Long-Duration Time Trial

The kinetics of recovery from neuromuscular fatigue resulting from exercise time trials (TTs) of different durations are not well-known. The aim of this study was to determine if TTs of three different durations would result in different short-term recovery in maximal voluntary contraction (MVC) and evoked peak forces. Twelve trained subjects performed repetitive concentric right knee extensions on an isokinetic dynamometer self-paced to last 3, 10, and 40 min (TTs). Neuromuscular function was assessed immediately (<2 s) and 1, 2, 4, and 8 min after completion of each TT using MVCs and electrical stimulation. Electrical stimulations consisted of single stimulus (SS), paired stimuli at 10 Hz (PS10), and paired stimuli at 100 Hz (PS100). Electrically evoked forces including the ratio of low- to high-frequency doublets were similar between trials at exercise cessation but subsequently increased more (P < 0.05) after the 3 min TT compared with either the 10 or 40 min TT when measured at 1 or 2 min of recovery. MVC force was not different between trials. The results demonstrate that recovery of peripheral fatigue including low-frequency fatigue depends on the duration and intensity of the preceding self-paced exercise. These differences in recovery probably indicate differences in the mechanisms of fatigue for these different TTs. Because recovery is faster after a 3 min TT than a 40 min TT, delayed assessment of fatigue will detect a difference in peripheral fatigue between trials that was not present at exercise cessation.

Neuromuscular function and fatigability in people diagnosed with head and neck cancer before versus after treatment

PURPOSE

Treatment for head and neck cancer is associated with multiple side effects, including loss of body mass, impaired physical function and reduced health-related quality of life. This study aimed to investigate the impact of treatment (radiation therapy ± concurrent chemotherapy) on (i) muscle strength, muscle cross-sectional area and patient-reported outcomes, and (ii) central and peripheral alterations during a whole-body exercise task.

METHODS

Ten people with head and neck cancer (4 female; 50 ± 9 years) completed a lab visit before and after (56 ± 30 days) completion of treatment. Participants performed a neuromuscular assessment (involving maximal isometric voluntary contractions in the knee extensors and electrical stimulation of the femoral nerve) before and during intermittent cycling to volitional exhaustion. Anthropometrics and patient-reported outcomes were also assessed.

RESULTS

From before to after treatment, maximal isometric muscle strength was reduced (P = 0.002, d = 0.73), as was potentiated twitch force (P < 0.001, d = 0.62), and muscle cross-sectional area (e.g., vastus lateralis: P = 0.010, d = 0.64). Exercise time was reduced (P = 0.008, d = 0.62) and peripheral processes contributed to a reduction in maximal force due to cycling. After treatment, the severity of self-reported fatigue increased (P = 0.041, r = - 0.65) and health-related quality of life decreased (P = 0.012, r = - 0.79).

CONCLUSION

Neuromuscular function was impaired in patients with head and neck cancer after treatment. Whole-body exercise tolerance was reduced and resulted in predominantly peripheral, rather than central, disturbances to the neuromuscular system. Future research should evaluate strength training after treatment for head and neck cancer, with the overall aim of reducing fatigue and improving health-related quality of life.

Effects of pre-induced fatigue vs. concurrent pain on exercise tolerance, neuromuscular performance and corticospinal responses of locomotor muscles

KEY POINTS

Fatigue and muscle pain induced in a remote muscle group has been shown to alter neuromuscular performance in exercising muscles. Inhibitory neural feedback associated with activation of mechano- and metabo-sensitive muscle afferents has been implicated in this phenomenon. The present study aimed to quantify and compare the effects of pre-induced fatigue and concurrent rising pain (evoked by muscle ischaemia) on the contralateral leg exercise capacity, neuromuscular performance, and corticomotor excitability and inhibition of knee extensor muscles. Pre-induced fatigue in one leg had a greater detrimental effect than the concurrent rising pain on the contralateral limb cycling capacity. Furthermore, pre-induced fatigue, but not concurrent rising pain, reduced corticospinal inhibition recorded from tested contralateral muscles. Regardless of the origin or mechanisms modulating sensory afferents during single-leg cycling exercise (i.e. pre-induced fatigue vs. concurrent rising pain), the limit of exercise tolerance remained the same and exercise was terminated upon achievement of a sensory tolerance limit.

ABSTRACT

Individuals often need to maintain voluntary contractions during high intensity exercise in the presence of fatigue and pain. This investigation examined the effects of pre-induced fatigue and concurrent rising pain (evoked by muscle ischaemia) in one leg on motor fatigability and corticospinal excitability/inhibition of the contralateral limb. Twelve healthy males undertook four experimental protocols including unilateral cycling to task failure at 80% of peak power output with: (i) the right-leg (RL); (ii) the left-leg (LL); (iii) RL immediately preceded by LL protocol (FAT-RL); and (iv) RL when blood flow was occluded in the contralateral (left) leg (PAIN-RL). Participants performed maximal and submaximal 5 s right-leg knee extensions during which transcranial magnetic and femoral nerve electrical stimuli were delivered to elicit motor-evoked and compound muscle action potentials, respectively. The pre-induced fatigue reduced the right leg cycling time-to-task failure (mean ± SD; 332 ± 137 s) to a greater extent than concurrent pain (460 ± 158 s), compared to RL (580 ± 226 s) (P < 0.001). The maximum voluntary contraction force declined less following FAT-RL (P < 0.019) and PAIN-RL (P < 0.032) compared to RL. Voluntary activation declined and the corticospinal excitability recorded from knee extensors increased similarly after the three conditions (P < 0.05). However, the pre-induced fatigue, but not concurrent pain, reduced corticospinal inhibition compared to RL (P < 0.05). These findings suggest that regardless of the origin and/or mechanisms modulating sensory afferent feedback during single-leg cycling (e.g. pre-induced fatigue vs. concurrent rising pain), the limit of exercise tolerance remains the same, suggesting that exercise will be terminated upon achievement of sensory tolerance limit.

Cycling performed on an innovative ergometer at different intensities-durations in men: neuromuscular fatigue and recovery kinetics

The majority of studies have routinely measured neuromuscular (NM) fatigue with a delay (∼1-3 min) after cycling exercises. This is problematic since NM fatigue can massively recover within the first 1-2 min after exercise. This study investigated the etiology of knee extensors (KE) NM fatigue and recovery kinetics in response to cycling exercises by assessing NM function as early as 10 s following cycling and up to 8 min of recovery. Ten young males performed different cycling exercises on different days: a Wingate (WING), a 10-min task at severe-intensity (SEV), and a 90-min task at moderate-intensity (MOD). Electrically evoked and isometric maximal voluntary contractions (IMVC) of KE were assessed before, after, and during recovery. SEV induced the highest decrease in IMVC. Peak twitch (Pt) was more reduced in WING and SEV than in MOD (p < 0.001), whereas voluntary activation decreased more after MOD than WING (p = 0.043). Regarding Pt and the ratio between low- and high-frequency doublet (i.e., low-frequency fatigue), recovery was faster for WING, whereas IMVC and high-frequency doublet recovered slower during MOD (p < 0.05). Our results confirm that peripheral fatigue is greater after WING and SEV, while central fatigue is greater following MOD. Peripheral fatigue can substantially recover within minutes after a supramaximal exercise while NM function recovered slower after prolonged, moderate-intensity exercise. This study provides an accurate estimation of NM fatigue and recovery kinetics because of dynamic exercise with large muscle mass by significantly shortening the delay for postexercise measurements.

Fatigue and recovery measured with dynamic properties versus isometric force: effects of exercise intensity

Although fatigue can be defined as an exercise-related decrease in maximal power or isometric force, most studies have assessed only isometric force. The main purpose of this experiment was to compare dynamic measures of fatigue [maximal torque (T _max), maximal velocity (V _max) and maximal power (P _max)] with measures associated with maximal isometric force [isometric maximal voluntary contraction (IMVC) and maximal rate of force development (MRFD)] 10 s after different fatiguing exercises and during the recovery period (1-8 min after). Ten young men completed six experimental sessions (3 fatiguing exercises×2 types of fatigue measurements). The fatiguing exercises were: 30 s all-out intensity (AI), 10 min at severe intensity (SI) and 90 min at moderate intensity (MI). Relative P _max decreased more than IMVC after AI exercise (P=0.005) while the opposite was found after SI (P=0.005) and MI tasks (P<0.001). There was no difference between the decrease in IMVC and T _max after the AI exercise, but IMVC decreased more than T _max immediately following and during the recovery from the SI (P=0.042) and MI exercises (P<0.001). Depression of MRFD was greater than V _max after all fatiguing exercises and during recovery (all P<0.05). Despite the general definition of fatigue, isometric assessment of fatigue is not interchangeable with dynamic assessment following dynamic exercises with large muscle mass of different intensities, i.e. the results from isometric function cannot be used to estimate dynamic function and vice versa. This implies different physiological mechanisms for the various measures of fatigue.

Acetaminophen ingestion improves muscle activation and performance during a 3-min all-out cycling test

Acute acetaminophen (ACT) ingestion has been shown to enhance cycling time-trial performance. The purpose of this study was to assess whether ACT ingestion enhances muscle activation and critical power (CP) during maximal cycling exercise. Sixteen active male participants completed two 3-min all-out tests against a fixed resistance on an electronically braked cycle ergometer 60 min after ingestion of 1 g of ACT or placebo (maltodextrin, PL). CP was estimated as the mean power output over the final 30 s of the test and W′ (the curvature constant of the power–duration relationship) was estimated as the work done above CP. The femoral nerve was stimulated every 30 s to measure membrane excitability (M-wave) and surface electromyography (EMGRMS) was recorded continuously to infer muscle activation. Compared with PL, ACT ingestion increased CP (ACT: 297 ± 32 W vs. PL: 288 ± 31 W, P < 0.001) and total work done (ACT: 66.4 ± 6.5 kJ vs. PL: 65.4 ± 6.4 kJ, P = 0.03) without impacting W′ (ACT: 13.1 ± 2.9 kJ vs. PL: 13.6 ± 2.4 kJ, P = 0.19) or the M-wave amplitude (P = 0.66) during the 3-min all-out cycling test. Normalised EMGRMS amplitude declined throughout the 3-min protocol in both PL and ACT conditions; however, the decline in EMGRMS amplitude was attenuated in the ACT condition, such that the EMGRMS amplitude was greater in ACT compared with PL over the last 60 s of the test (P = 0.04). These findings indicate that acute ACT ingestion might increase performance and CP during maximal cycling exercise by enhancing muscle activation.

The short-term recovery of corticomotor responses in elbow flexors

Background

The recovery of neurophysiological parameters at various time intervals following fatiguing exercise has been investigated previously. However, the repetition of neuromuscular assessments during the recovery period may have interfered with the true corticomotor excitability responses. In this experiment, fatiguing contractions were combined with a single post-fatigue assessment at varying time points. Ten participants undertook 5 bouts of 60-s maximal voluntary contractions (MVC) of the elbow flexors, separated by 20 min. Before and after each 60-s fatiguing exercise (FAT), participants performed a series of 6-s contractions at 100, 75 and 50% of their MVC during which transcranial magnetic, transmastoid electrical and brachial plexus electrical stimuli were used to elicit motor evoked potentials (MEP), cervicomedullary motor evoked potentials (CMEP) and compound muscle action potentials (Mmax) in the biceps brachii muscle, respectively. Post-FAT measurements were randomly performed 0, 15, 30, 60, or 120 s after each FAT.

Results

MVC force declined to 65.1 ± 13.1% of baseline following FAT and then recovered to 82.7 ± 10.2% after 60 s. The MEP·Mmax⁻¹ ratio recorded at MVC increased to 151.1 ± 45.8% and then returned to baseline within 60 s. The supraspinal excitability (MEP·CMEP⁻¹) measured at MVC increased to 198.2 ± 47.2% and fully recovered after 30 s. The duration of post-MEP silent period recorded at MVC elongated by 23.4 ± 10.6% during FAT (all P < 0.05) but fully recovered after 15 s.

Conclusions

The current study represents the first accurate description of the time course and pattern of recovery for supraspinal and spinal excitability and inhibition following a short maximal fatiguing exercise in upper limb.

Acute ibuprofen ingestion does not attenuate fatigue during maximal intermittent knee extensor or all-out cycling exercise

Recent research suggests that acute consumption of pharmacological analgesics can improve exercise performance, but the ergogenic potential of ibuprofen (IBP) administration is poorly understood. This study tested the hypothesis that IBP administration would enhance maximal exercise performance. In one study, 13 physically active males completed 60 × 3-s maximal voluntary contractions (MVCs) of the knee extensors interspersed with 2-s passive recovery periods, on 2 occasions, with the critical torque (CT) estimated as the mean torque over the last 12 contractions (part A). In another study, 16 active males completed two 3-min all-out tests against a fixed resistance on an electronically braked cycle ergometer, with the critical power estimated from the mean power output over the final 30 s of the test (part B). All tests were completed 60 min after ingestion of maltodextrin (placebo, PL) or 400 mg of IBP. Peripheral nerve stimulation was administered at regular intervals and electromyography was measured throughout. For part A, mean torque (IBP: 60% ± 13% of pre-exercise MVC; PL: 58% ± 14% of pre-exercise MVC) and CT (IBP: 41% ± 16% of pre-exercise MVC; PL: 40% ± 15% of pre-exercise MVC) were not different between conditions (P > 0.05). For part B, end-test power output (IBP: 292 ± 28 W; PL: 288 ± 31 W) and work done (IBP: 65.9 ± 5.9 kJ; PL: 65.4 ± 6.4 kJ) during the 3-min all-out cycling tests were not different between conditions (all P > 0.05). For both studies, neuromuscular fatigue declined at a similar rate in both conditions (P > 0.05). In conclusion, acute ingestion of 400 mg of IBP does not improve single-leg or maximal cycling performance in healthy humans.

The role of the nervous system in neuromuscular fatigue induced by ultra-endurance exercise

Ultra-endurance events are not a recent development but they have only become very popular in the last 2 decades, particularly ultramarathons run on trails. The present paper reviews the role of the central nervous system in neuromuscular fatigue induced by ultra-endurance exercise. Large decreases in voluntary activation are systematically found in ultra-endurance running but are attenuated in ultra-endurance cycling for comparable intensity and duration. This indirectly suggests that afferent feedback, rather than neurobiological changes within the central nervous system, is determinant in the amount of central fatigue produced. Whether this is due to inhibition from type III and IV afferent fibres induced by inflammation, disfacilitation of Ia afferent fibers owing to repeated muscle stretching or other mechanisms still needs to be determined. Sleep deprivation per se does not seem to play a significant role in central fatigue although it still affects performance by elevating ratings of perceived exertion. The kinetics of central fatigue and recovery, the influence of muscle group (knee extensors vs plantar flexors) on central deficit as well as the limitations related to studies on central fatigue in ultra-endurance exercise are also discussed in the present article. To date, no study has quantified the contribution of spinal modulations to central fatigue in ultra-endurance events. Future investigations utilizing spinal stimulation (i.e., thoracic stimulation) must be conducted to assess the role of changes in motoneuronal excitability on the observed central fatigue. Recovery after ultra-endurance events and the effect of sex on neuromuscular fatigue must also be studied further.