Circulating Gal-3 and sST2 are associated with acute exercise-induced sustained endothelial activation: Possible relevance for fibrosis development?

Long-term, intense endurance exercise training can occasionally induce endothelial micro-damage and cardiac fibrosis. The underlying mechanisms are incompletely understood. Twenty healthy, well-trained male participants (10 runners and 10 cyclists) performed a strenuous high-intensity interval training (HIIT) session matched by age, height, weight and maximal oxygen consumption. We assessed the acute exercise response of novel cardiac biomarkers of fibrosis [e.g., galectin-3 (Gal-3) and soluble suppression of tumorigenicity 2 (sST2)] per exercise modality and their relationship with haemodynamic contributors, such as preload, afterload and cardiac contractility index (CTi), in addition to endothelial damage by sustained activation and shedding of endothelial cells (ECs). Serum Gal-3 and sST2 concentrations were investigated by enzyme-linked immunosorbent assays; haemodynamics were analysed via impedance plethysmography and circulating ECs by flow cytometry. The Gal-3 and sST2 concentrations and ECs were elevated after exercise (P < 0.001), without interaction between exercise modalities. Circulating Gal-3 and sST2 concentrations both showed a positive relationship with ECs (rrm  = 0.68, P = 0.001 and rrm  = 0.57, P = 0.010, respectively, both n = 18). The EC association with Gal-3 was significant only in cyclists, but equally strong for both modalities. Gal-3 was also related to exercise-induced CTi (rrm  = 0.57, P = 0.011, n = 18). Cardiac wall stress is increased after an acute HIIT session but does not differ between exercise modalities. Exercise-released Gal-3 from cardiac macrophages could very probably drive systemic endothelial damage, based on an enhanced CTi. The importance of acute exercise-induced vascular resistances and cardiac contractility for the release of fibrotic biomarkers and any long-term pathological endothelial adaptation should be investigated further, also relative to the exercise modality. NEW FINDINGS: What is the central question of this study? Circulating biomarkers of cardiac wall stress and fibrosis are influenced by physical exercise. The underlying mechanisms per exercise modality are still unclear. What is the main finding and its importance? We show that galectin-3 (Gal-3) and soluble suppression of tumorigenicity 2 (sST2) are increased after acute exercise but do not differ between running and cycling. One haemodynamic contributor to the secretion of Gal-3 is an enhanced cardiac contractility. Acute exercise-released Gal-3 and sST2 are linked to sustained endothelial activation and cell shedding. This could be relevant in the context of fibrosis development and could identify athletes at risk for pathological endothelial adaptations.

Inspiratory response and side-effects to rapid bilateral magnetic phrenic nerve stimulation using differently shaped coils: implications for stimulation-assisted mechanical ventilation.

BACKGROUND: Rapid magnetic stimulation (RMS) of the phrenic nerves may serve to attenuate diaphragm atrophy during mechanical ventilation. With different coil shapes and stimulation location, inspiratory responses and side-effects may differ. This study aimed to compare the inspiratory and sensory responses of three different RMS-coils either used bilaterally on the neck or on the chest, and to determine if ventilation over 10 min can be achieved without muscle fatigue and coils overheating. METHODS: Healthy participants underwent bilateral anterior 1-s RMS on the neck (RMSBAMPS) (N = 14) with three different pairs of magnetic coils (parabolic, D-shape, butterfly) at 15, 20, 25 and 30 Hz stimulator-frequency and 20% stimulator-output with + 10% increments. The D-shape coil with individual optimal stimulation settings was then used to ventilate participants (N = 11) for up to 10 min. Anterior RMS on the chest (RMSaMS) (N = 8) was conducted on an optional visit. Airflow was assessed via pneumotach and transdiaphragmatic pressure via oesophageal and gastric balloon catheters. Perception of air hunger, pain, discomfort and paresthesia were measured with a numerical scale. RESULTS: Inspiration was induced via RMSBAMPS in 86% of participants with all coils and via RMSaMS in only one participant with the parabolic coil. All coils produced similar inspiratory and sensory responses during RMSBAMPS with the butterfly coil needing higher stimulator-output, which resulted in significantly larger discomfort ratings at maximal inspiratory responses. Ten of 11 participants achieved 10 min of ventilation without decreases in minute ventilation (15.7 ± 4.6 L/min). CONCLUSIONS: RMSBAMPS was more effective than RMSaMS, and could temporarily ventilate humans seemingly without development of muscular fatigue. Trial registration This study was registered on clinicaltrials.gov (NCT04176744).

Respiratory muscle endurance training improves exercise performance but does not affect resting blood pressure and sleep in healthy active elderly.

PURPOSE: Ageing is associated with increased blood pressure (BP), reduced sleep, decreased pulmonary function and exercise capacity. The main purpose of this study was to test whether respiratory muscle endurance training (RMET) improves these parameters. METHODS: Twenty-four active normotensive and prehypertensive participants (age: 65.8 years) were randomized and balanced to receive either RMET (N = 12) or placebo (PLA, N = 12). RMET consisted of 30 min of volitional normocapnic hyperpnea at 60% of maximal voluntary ventilation while PLA consisted of 1 inhalation day-1 of a lactose powder. Both interventions were performed on 4-5 days week-1 for 4-5 weeks. Before and after the intervention, resting BP, pulmonary function, time to exhaustion in an incremental respiratory muscle test (incRMET), an incremental treadmill test (IT) and in a constant-load treadmill test (CLT) at 80% of peak oxygen consumption, balance, sleep at home, and body composition were assessed. Data was analyzed with 2 × 2 mixed ANOVAs. RESULTS: Compared to PLA, there was no change in resting BP (independent of initial resting BP), pulmonary function, IT performance, sleep, body composition or balance (all p > 0.05). Performance significantly increased in the incRMET (+ 6.3 min) and the CLT (+ 3.2 min), resulting in significant interaction effects (p < 0.05). CONCLUSION: In the elderly population, RMET might be used to improve respiratory and whole body endurance performance either as an adjunct to physical exercise training or as a replacement thereof for people not being able to intensively exercise even if no change in BP or sleep may be expected.

A Thermal Skin Model for Comparing Contact Skin Temperature Sensors and Assessing Measurement Errors.

To improve the measurement and subsequent use of human skin temperature (Tsk) data, there is a need for practical methods to compare Tsk sensors and to quantify and better understand measurement error. We sought to develop, evaluate, and utilize a skin model with skin-like thermal properties as a tool for benchtop Tsk sensor comparisons and assessments of local temperature disturbance and sensor bias over a range of surface temperatures. Inter-sensor comparisons performed on the model were compared to measurements performed in vivo, where 14 adult males completed an experimental session involving rest and cycling exercise. Three types of Tsk sensors (two of them commercially available and one custom made) were investigated. Skin-model-derived inter-sensor differences were similar (within ±0.4 °C) to the human trial when comparing the two commercial Tsk sensors, but not for the custom Tsk sensor. Using the skin model, all surface Tsk sensors caused a local temperature disturbance with the magnitude and direction dependent upon the sensor and attachment and linearly related to the surface-to-environment temperature gradient. Likewise, surface Tsk sensors also showed bias from both the underlying disturbed surface temperature and that same surface in its otherwise undisturbed state. This work supports the development and use of increasingly realistic benchtop skin models for practical Tsk sensor comparisons and for identifying potential measurement errors, both of which are important for future Tsk sensor design, characterization, correction, and end use.

ERS statement on respiratory muscle testing at rest and during exercise.

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

Similar Airway Function after Volitional Hyperpnea in Mild-Moderate Asthmatics and Healthy Controls.

BACKGROUND: The beneficial effects of exercise training for asthmatics might relate to repetitive airway stretching. Thus, a training with more pronounced airway stretch using isolated, volitional hyperpnea (HYP) might be similarly or more effective. However, in healthy subjects, a bout of HYP training is known to cause an acute FEV1 decline. OBJECTIVE: The aim of the present study was therefore to test whether these changes are more pronounced in asthmatics, possibly putting them at risk with HYP training. METHODS: Nine subjects with mild-moderate asthma (confirmed by mannitol challenge) and 11 healthy subjects performed six 5-min bouts (with 6-min breaks; HYP1) and one 30-min bout (HYP2) of normocapnic HYP at 60% of maximal voluntary ventilation using warm and humid air. FEV1 and airway resistance (R5) were measured before, in breaks (HYP1), and immediately after HYP, and during 60 min of recovery. RESULTS: In both groups, a significant and similar decrease in FEV1 during HYP1 (asthmatics: -3 ± 3%; healthy subjects: -2 ± 3%), after HYP1 (asthmatics: -2 ± 5%; healthy subjects: -1 ± 4%), and after HYP2 (asthmatics: -4 ± 5%; healthy subjects: -3 ± 3%), and an increase in R5 during and after both HYPs were observed. Maximal changes in FEV1 and R5 did not correlate with baseline lung function or responsiveness to mannitol. CONCLUSIONS: A bout of HYP does not lead to relevant bronchoconstriction and the observed changes in lung function and airway resistance are neither of the magnitude of clinical relevance, nor do they differ from responses in healthy individuals. Thus, HYP training can safely be tested as an airway-specific exercise training alternative (or add-on) modality to regular aerobic exercise training.

Validity of contact skin temperature sensors under different environmental conditions with and without fabric coverage: characterisation and correction.

Contact skin temperature (Tsk) sensors are calibrated under uniform thermal conditions but used in the presence of a skin-to-environment temperature gradient. We aimed to characterise the validity of contact Tsk sensors when measuring surface temperature under a range of environmental and fabric coverage conditions, to estimate practical temperature limits for a given measurement bias and to explore correcting for bias. Using two types of contact Tsk sensors (thermistors, n = 5; iButtons, n = 5), we performed experiments in three phases: (1) conventional calibration (uniform thermal environment) over 15-40 °C in 5 °C steps (at t = 0, and 24 h, 12 weeks later), (2) surface temperature measurements of a purpose-made aluminium plate (also 15-40 °C) at different environmental temperatures (15, 25, 35 °C) with different sensor attachments and fabric coverings to assess measurement bias and calculate correction factors that account for the next-to-surface microclimate temperature and (3) surface measurements (33.1 °C in 20 °C environment) for assessing generated corrections. The main results were as follows: (1) after initial calibration, Tsk sensors were valid under uniform thermal conditions [mean bias < 0.05 °C, typical error of the estimate < 0.1 °C]. (2) For the surface measurements, bias increased with increasing surface-to-microclimate temperature difference for both sensor types. The range of surface temperatures possible to remain within given bias limits could be estimated for the various conditions. (3) For a given measurement, using corrections encompassing the microclimate temperature (mean difference - 0.1 to 0.5 °C) performed better than conventional calibration alone (mean difference - 2.1 to - 0.3 °C). In conclusion, the bias of Tsk sensors is influenced by the microclimate temperature and, therefore, body coverings. Where excessive bias is expected, the validity can be improved through sensor and attachment selection and by applying corrections that account for the local temperature gradient.

Locomotor and diaphragm muscle fatigue in endurance athletes performing time-trials of different durations.

PURPOSE: Fatigue in leg muscles might differ between running and cycling due to inherent differences in muscle activation patterns. Moreover, postural demand placed upon the diaphragm during running could augment the development of diaphragm fatigue. METHODS: We investigated quadriceps and diaphragm fatigue in 11 runners and 11 cyclists (age: 29 ± 5 years; [Formula: see text]O2,peak: 66.9 ± 5.5 ml min(-1) kg(-1)) by assessing quadriceps twitch force (Q tw) and transdiaphragmatic twitch pressure (P di,tw) before and after 15- and 30-min time-trials (15TT, 30TT). Inspiratory muscle fatigue was also obtained after volitional normocapnic hyperpnoea (NH) where postural demand is negligible. We hypothesized that running and cycling would induce different patterns of fatigue and that runners would develop less respiratory muscle fatigue when performing NH. RESULTS: The reduction in Q tw was greater in cyclists (32 ± 6 %) compared to runners (13 ± 8 %, p < 0.01), but not different for 15TTs (23 ± 13 %) and 30TTs (21 ± 11 %, p = 0.34). Overall P di,tw was more reduced after 15TTs (24 ± 8 %) than after 30TTs (20 ± 9 %, p = 0.04) while being similar for runners and cyclists (p = 0.78). Meanwhile, breathing duration in NH and the magnitude of inspiratory muscle fatigue were also not different (both p > 0.05). CONCLUSION: Different levels of leg muscle fatigue in runners and cyclists could in part be related to the specific muscle activation patterns including concentric contractions in both modalities but eccentric contractions in runners only. Diaphragm fatigue likely resulted from the large ventilatory load which is characteristic for both exercise modalities and which was higher in 15TTs than in 30TTs (+27 %, p < 0.01) while postural demand appears to be of less importance.

Energy expenditure estimation during activities of daily living in middle-aged and older adults using an accelerometer integrated into a hearing aid.

Background: Accelerometers were traditionally worn on the hip to estimate energy expenditure (EE) during physical activity but are increasingly replaced by products worn on the wrist to enhance wear compliance, despite potential compromises in EE estimation accuracy. In the older population, where the prevalence of hearing loss is higher, a new, integrated option may arise. Thus, this study aimed to investigate the accuracy and precision of EE estimates using an accelerometer integrated into a hearing aid and compare its performance with sensors simultaneously worn on the wrist and hip. Methods: Sixty middle-aged to older adults (average age 64.0 ± 8.0 years, 48% female) participated. They performed a 20-min resting energy expenditure measurement (after overnight fast) followed by a standardized breakfast and 13 different activities of daily living, 12 of them were individually selected from a set of 35 activities, ranging from sedentary and low intensity to more dynamic and physically demanding activities. Using indirect calorimetry as a reference for the metabolic equivalent of task (MET), we compared the EE estimations made using a hearing aid integrated device (Audéo) against those of a research device worn on the hip (ZurichMove) and consumer devices positioned on the wrist (Garmin and Fitbit). Class-estimated and class-known models were used to evaluate the accuracy and precision of EE estimates via Bland-Altman analyses. Results: The findings reveal a mean bias and 95% limit of agreement for Audéo (class-estimated model) of -0.23 ± 3.33 METs, indicating a slight advantage over wrist-worn consumer devices (Garmin: -0.64 ± 3.53 METs and Fitbit: -0.67 ± 3.40 METs). Class-know models reveal a comparable performance between Audéo (-0.21 ± 2.51 METs) and ZurichMove (-0.13 ± 2.49 METs). Sub-analyses show substantial variability in accuracy for different activities and good accuracy when activities are averaged over a typical day's usage of 10 h (+61 ± 302 kcal). Discussion: This study shows the potential of hearing aid-integrated accelerometers in accurately estimating EE across a wide range of activities in the target demographic, while also highlighting the necessity for ongoing optimization efforts considering precision limitations observed across both consumer and research devices.

Effect of inspiratory muscle fatigue on exercise performance taking into account the fatigue-induced excess respiratory drive.

Inspiratory muscle fatigue (IMF) is suggested to compromise exercise performance, possibly via a respiratory muscle metaboreflex that impairs blood flow to working muscles, thereby accelerating the development of fatigue in these muscles. Cycling with IMF has also been associated with an excess ventilatory response, which could per se impair performance. Therefore, the present study investigated whether prior-induced IMF would affect subsequent cycling performance via increased quadriceps muscle fatigue alone and whether fatigue-induced excess ventilation would contribute to this impairment. Fourteen healthy male subjects (peak oxygen uptake, 57.0 ± 5.5 ml min(-1) kg(-1)) cycled to exhaustion at 85% of their maximal work output with prior-induced IMF (PF-EX) and without prior-induced IMF (C-EX). Subjects then cycled twice for the duration of PF-EX but without prior IMF, once with spontaneous breathing (C-ISO) and once with breathing coached to match PF-EX ventilation (MATCH-ISO). Inspiratory muscle (P(tw)) and quadriceps muscle contractility (Q(tw)) was assessed via magnetic nerve stimulation before and after exercise. The time to exhaustion in the PF-EX conditions was significantly reduced by 14% compared with C-EX. The reduction in P(tw) and Q(tw) was greater after PF-EX (P(tw), 17.3 ± 9.7%; Q(tw), 32.0 ± 10.8%) than after MATCH-ISO (P(tw), 10.8 ± 10.3%; Q(tw), 23.3 ± 15.2%; P < 0.05), which may explain the increased perception of exertion and earlier task failure with prior-induced IMF. The augmented ventilatory drive had no effect on reductions in P(tw) and Q(tw) after MATCH-ISO compared with C-ISO. Thus, prior-induced IMF reduces exercise performance, probably as a result of the increased quadriceps muscle fatigue and thus greater perception of exertion independent of the excess respiratory drive when cycling with fatigued inspiratory muscles.

Sex differences in quadriceps and inspiratory muscle fatigability following high-intensity cycling.

OBJECTIVES: As females have been hypothesized to have more fatigue resistant inspiratory muscles, this study aimed to compare the development of inspiratory and leg muscle fatigue between males and females following high-intensity cycling. DESIGN: Cross-sectional comparison. METHODS: 17 healthy young males (27 ±â€¯6 years, V̇O2peak 55 ±â€¯10 mlï½¥min-1ï½¥kg-1) and females (25 ±â€¯4 years, V̇O2peak 45 ±â€¯7 mlï½¥min-1ï½¥kg-1) cycled until exhaustion at 90% of the peak power output achieved during an incremental test. Changes in quadriceps and inspiratory muscle function were assessed via maximal voluntary contractions (MVC) and assessments of contractility via electrical stimulation of the femoral nerve and cervical magnetic stimulation of the phrenic nerves. RESULTS: Time to exhaustion was similar between sexes (p = 0.270, 95% CI -2.4 - 0.7 min). MVC of the quadriceps was lower after cycling for males (83.9 ±â€¯11.5% vs. 94.0 ±â€¯12.0% of baseline for females, p = 0.018). Reductions in twitch forces were not different between sexes for the quadriceps (p = 0.314, 95% CI -5.5 - 16.6 percent-points) or inspiratory muscles (p = 0.312, 95% CI -4.0 - 2.3 percent-points). Changes in inspiratory muscle twitches were unrelated to the different measures of quadriceps fatigue. CONCLUSION: Females incur similar peripheral fatigue in the quadriceps and inspiratory muscles compared with men following high-intensity cycling, despite smaller reduction in voluntary force. This small difference alone does not seem sufficient to warrant different training strategies to be recommended for women.

Effects of Sprint Interval and Endurance Respiratory Muscle Training on Postcycling Inspiratory and Quadriceps Fatigue.

PURPOSE: We investigated whether a 4-wk period of respiratory muscle endurance training (RMET) or respiratory muscle sprint interval training (RMSIT) would lead to an attenuation of inspiratory muscle and quadriceps fatigue after a bout of high-intensity cycling compared with a placebo intervention (PLAT), as predicted by the respiratory metaboreflex model. METHODS: Thirty-three active, young healthy adults performed RMET, RMSIT, or PLAT. Changes in inspiratory muscle and quadriceps twitches in response to a cycling test at 90% of peak work capacity were assessed before and after training. EMG activity and deoxyhemoglobin (HHb, via near-infrared spectroscopy) of the quadriceps and inspiratory muscles were also monitored during the cycling test, along with cardiorespiratory and perceptual variables. RESULTS: At pretraining, cycling reduced the twitch force of the inspiratory muscles (86% ± 11% baseline) and quadriceps (66% ± 16% baseline). Training did not attenuate the drop in twitch force of the inspiratory muscles (PLAT, -3.5 ± 4.9 percent-points [p.p.]; RMET, 2.7 ± 11.3 p.p.; RMSIT, 4.1 ± 8.5 p.p.; group-training interaction, P = 0.394) or quadriceps (PLAT, 3.8 ± 18.6 p.p.; RMET, -2.6 ± 14.0 p.p.; RMSIT, 5.2 ± 9.8 p.p.; group-training interaction P = 0.432). EMG activity and HHb levels during cycling did not change after training for either group. Only RMSIT showed a within-group decrease in the perception of respiratory exertion with training. CONCLUSIONS: Four weeks of RMET or RMSIT did not attenuate the development of exercise-induced inspiratory or quadriceps fatigue. The ergogenic effects of respiratory muscle training during whole-body exercise might be related to an attenuation of perceptual responses.

Similar effects on exercise performance following different respiratory muscle training programs in healthy young men.

Both respiratory muscle endurance training (RMET) and inspiratory resistive training (IMT) seem to increase whole-body exercise performance, but direct comparisons between the two are scarce. We hypothesized that the similarity of RMET to exercise-induced ventilation would induce larger improvements compared to IMT. Twenty-six moderately-trained men performed either 4 weeks of RMET, IMT or SHAM training. Before and after the interventions, respiratory muscle endurance, 3-km running time-trial performance and leg muscle fatigue after intense constant-load cycling (assessed with femoral nerve magnetic stimulation) were measured. Both RMET (+ 59%) and IMT (+ 38%) increased respiratory muscle endurance (both p < 0.01 vs. SHAM) but only IMT increased inspiratory strength (+ 32%, p < 0.001 vs. SHAM). 3-km time improved showing a main effect of training (p = 0.026), however with no differences between groups. Leg fatigue after cycling was not attenuated with training (p = 0.088 for group-training interaction). All groups showed a significant (~ 0.3 l) increase in average tidal volume during cycling exercise combined with a concomitant reduction in respiratory exertion. While RMET and IMT improved specific aspects of respiratory muscles performance, no benefits beyond SHAM were seen during whole-body exercise. Changes in respiratory sensations might be a result of altered breathing pattern.

3D Atrial Strain for Predicting Recurrence of Atrial Fibrillation after Pulmonary Vein Isolation.

AIMS: Association of two-(2D) and three-dimensional (3D) left atrial strain (LAS) and low-voltage area (LVA) with recurrence of atrial fibrillation (AF) after pulmonary vein isolation (PVI) was assessed. METHODS AND RESULTS: 3D LAS, 2D LAS, and LVA were obtained in 93 consecutive patients undergoing PVI and recurrence of AF was analyzed prospectively. AF recurred in 12 patients (13%). The 3D left atrial reservoir strain (LARS) and pump strain (LAPS) were lower in patients with recurrent AF than without (p = 0.008 and p = 0.009, respectively). In univariable Cox regression, 3D LARS or LAPS were associated with recurrent AF (LARS: HR = 0.89 (0.81-0.99), p = 0.025; LAPS: HR = 1.40 (1.02-1.92), p = 0.040), while other values were not. Association of 3D LARS or LAPS with recurrent AF was independent of age, body mass index, arterial hypertension, left ventricular ejection fraction, and end-diastolic volume index and left atrial volume index in multivariable models. Kaplan-Meier curves revealed that patients with 3D LAPS < -5.9% did not exhibit recurrent AF, while those >-5.9% had a significant risk of recurrent AF. CONCLUSIONS: 3D LARS and LAPS were associated with recurrent AF after PVI. Association of 3D LAS was independent of relevant clinical and echocardiographic parameters and improved their predictive value. Hence, they may be applied for outcome prediction in patients undergoing PVI.

Spinal opioid receptor-sensitive muscle afferents contribute to the fatigue-induced increase in intracortical inhibition in healthy humans.

We investigated the influence of spinal opioid receptor-sensitive muscle afferents on cortical changes following fatiguing unilateral knee-extensor exercise. On separate days, seven subjects performed an identical five sets of intermittent isometric right-quadriceps contractions, each consisting of eight submaximal contractions [63 ± 7% maximal voluntary contraction (MVC)] and one MVC. The exercise was performed following either lumbar interspinous saline injection or lumbar intrathecal fentanyl injection blocking the central projection of spinal opioid receptor-sensitive lower limb muscle afferents. To quantify exercise-induced peripheral fatigue, quadriceps twitch force (Q(tw,pot)) was assessed via supramaximal magnetic femoral nerve stimulation before and after exercise. Motor evoked potentials and cortical silent periods (CSPs) were evaluated via transcranial magnetic stimulation of the motor cortex during a 3% MVC pre-activation period immediately following exercise. End-exercise quadriceps fatigue was significant and similar in both conditions (Q(tw,pot) -35 and -39% for placebo and fentanyl, respectively; P = 0.38). Immediately following exercise on both days, motor evoked potentials were similar to those obtained prior to exercise. Compared with pre-exercise baseline, CSP in the placebo trial was 21 ± 5% longer postexercise (P < 0.01). In contrast, CSP following the fentanyl trial was not significantly prolonged compared with the pre-exercise baseline (6 ± 4%). Our findings suggest that the central effects of spinal opioid receptor-sensitive muscle afferents might facilitate the fatigue-induced increase in CSP. Furthermore, since the CSP is thought to reflect inhibitory intracortical interneuron activity, which may contribute to central fatigue, our findings imply that spinal opioid receptor-sensitive muscle afferents might influence central fatigue by facilitating intracortical inhibition.

Corrigendum: Acute Exercise-Induced Oxidative Stress Does Not Affect Immediate or Delayed Precursor Cell Mobilization in Healthy Young Males.

[This corrects the article DOI: 10.3389/fphys.2020.577540.].

Current limits for flowmeter resistance in metabolic carts can negatively affect exercise performance.

PURPOSE: To investigate whether a metabolic cart using a flowmeter in the upper range of accepted resistance to airflow (<1.5 cmH2 O∙L-1 ∙s-1 for flows up to 14 L∙s-1 , American Thoracic Society) negatively impacts exercise performance in healthy individuals. METHODS: 16 recreationally active males (age 25 ± 1 years, height 180 ± 6 cm, weight 73.5 ± 5.8 kg, all mean ± SD) performed two incremental tests on a bicycle ergometer on each of two visits, using a metabolic cart with a flowmeter of either low (Oxycon Pro) or high (Innocor) airflow resistance. Mouth pressures, gas exchange, blood lactate concentration [La- ], perception of breathlessness, respiratory, and leg exertion were assessed throughout the tests. RESULTS: Tests performed with the Innocor were significantly shorter (15.3 ± 3.2 vs. 15.8 ± 3.3 min, p < 0.0001) and showed higher maximal flow resistance (1.3 ± 0.2 vs. 0.3 ± 0.0 cmH2 O∙L-1 ∙s-1 , p < 0.0001). At end-exercise, peak oxygen consumption (-200 ± 220 ml.min-1 , p < 0.0001), minute ventilation (-19.9 ± 10.5 L.min-1 , p < 0.0001), breathing frequency (-5.4 ± 5.2 breaths.min-1 , p < 0.0001), heart rate (-2.1 ± 3.6 bpm, p = 0.002) and [La- ] (-0.7 ± 1.0 mmol.L-1 , p < 0.0001), but not tidal volume (-0.1 ± 0.2 L, p = 0.172) were lower with the Innocor, while the perception of breathlessness was higher (+3.8 ± 5.1 points, p < 0.0001). CONCLUSIONS: Airflow resistance in the upper range of current guidelines can significantly affect exercise performance and respiratory pattern in young, healthy males during incremental exercise. The present results indicate the need to revisit guidelines for devices used in ergospirometry.

Cardiorespiratory Responses to Constant and Varied-Load Interval Training Sessions.

PURPOSE: To compare the cardiorespiratory responses of a traditional session of high-intensity interval training session with that of a session of similar duration and average load, but with decreasing workload within each bout in cyclists and runners. METHODS: A total of 15 cyclists (maximal oxygen uptake [V˙O2max] 62 [6] mL·kg-1·min-1) and 15 runners (V˙O2max 58 [4] mL·kg-1·min-1) performed both sessions at the maximal common tolerable load on different days. The sessions consisted of four 4-minute intervals interspersed with 3 minutes of active recovery. Power output was held constant for each bout within the traditional day, whereas power started 40 W (2 km·h-1) higher and finished 40 W (2 km·h-1) lower than average within each bout of the decremental session. RESULTS: Average oxygen uptake during the high-intensity intervals was higher in the decremental session in cycling (89 [4]% vs 86 [5]% of V˙O2max, P = .002) but not in running (91 [4]% vs 90 [4]% of V˙O2max, P = .38), as was the time spent >90% of V˙O2max and the time spent >90% of peak heart rate. Average heart rate (P < .001), pulmonary ventilation (P < .001), and blood lactate concentration (P < .001) were higher during the decremental sessions in both cycling and running. CONCLUSIONS: Higher levels of physiological perturbations were achieved during decremental sessions in both cycling and running. These differences were, however, more prominent in cycling, thus making cycling a more attractive modality for testing the effects of a training intervention.

Fatigue Monitoring Through Wearables: A State-of-the-Art Review.

The objective measurement of fatigue is of critical relevance in areas such as occupational health and safety as fatigue impairs cognitive and motor performance, thus reducing productivity and increasing the risk of injury. Wearable systems represent highly promising solutions for fatigue monitoring as they enable continuous, long-term monitoring of biomedical signals in unattended settings, with the required comfort and non-intrusiveness. This is a p rerequisite for the development of accurate models for fatigue monitoring in real-time. However, monitoring fatigue through wearable devices imposes unique challenges. To provide an overview of the current state-of-the-art in monitoring variables associated with fatigue via wearables and to detect potential gaps and pitfalls in current knowledge, a systematic review was performed. The Scopus and PubMed databases were searched for articles published in English since 2015, having the terms "fatigue," "drowsiness," "vigilance," or "alertness" in the title, and proposing wearable device-based systems for non-invasive fatigue quantification. Of the 612 retrieved articles, 60 satisfied the inclusion criteria. Included studies were mainly of short duration and conducted in laboratory settings. In general, researchers developed fatigue models based on motion (MOT), electroencephalogram (EEG), photoplethysmogram (PPG), electrocardiogram (ECG), galvanic skin response (GSR), electromyogram (EMG), skin temperature (Tsk), eye movement (EYE), and respiratory (RES) data acquired by wearable devices available in the market. Supervised machine learning models, and more specifically, binary classification models, are predominant among the proposed fatigue quantification approaches. These models were considered to perform very well in detecting fatigue, however, little effort was made to ensure the use of high-quality data during model development. Together, the findings of this review reveal that methodological limitations have hindered the generalizability and real-world applicability of most of the proposed fatigue models. Considerably more work is needed to fully explore the potential of wearables for fatigue quantification as well as to better understand the relationship between fatigue and changes in physiological variables.