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.

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.

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.

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.

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.

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.

MiRNA126 - RGS16 - CXCL12 Cascade as a Potential Mechanism of Acute Exercise-Induced Precursor Cell Mobilization.

Acute exercise enhances circulating stem and precursor cells (CPCs) in the peripheral blood. The responsible mechanisms and molecular pathways, however, have not been fully identified. The aim of the present study was to investigate a pathway related to elevated levels of apoptotic peripheral blood mononuclear cells (MNCs) and their secretome. An increased uptake of miRNA126 in MNCs was suggested to lead to reduced levels of RGS16 mRNA and, in turn, an enhanced translation and secretion of CXCL12. Eighteen healthy, young men underwent two identical incremental cycling exercises of which the first served as control while the second was preceded by a 7-day-long antioxidative supplementation. Blood samples were collected at baseline (-10min) and several time points after exercise (0, 30, 90, 180, and 270min). Relative concentrations of miRNA126 in MNCs and CXCL12 levels in plasma were determined at all time points while RGS16 mRNA was assessed in MNCs at baseline and 30min after exercise. CXCL12 increased after exercise and strongly correlated with CPC numbers. MiRNA126 increased 30min and, to a lesser extent, also 180 and 270min after exercise but only with supplementation. RGS16 mRNA decreased 30min after exercise independent of the intervention. The amount of RGS16 mRNA inversely correlated with levels of miRNA126, but not with plasma CXCL12. In conclusion, even though plasma CXCL12 correlated with CPC numbers, the increase in CXCL12 cannot be explained by the increased concentration of miRNA126 and lower RGS16 mRNA in MNCs that would have allowed for an enhanced translation of CXCL12. Clinical Trial Registration: ClinicalTrials.gov, NCT03747913. Registered 20 November 2018, https://clinicaltrials.gov/ct2/show/NCT03747913.

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.].

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.

Enhanced Deep-Inspiration Breath Hold Superior to High-Frequency Percussive Ventilation for Respiratory Motion Mitigation: A Physiology-Driven, MRI-Guided Assessment Toward Optimized Lung Cancer Treatment With Proton Therapy.

Background: To safely treat lung tumors using particle radiation therapy (PRT), motion-mitigation strategies are of critical importance to ensure precise irradiation. Therefore, we compared applicability, effectiveness, reproducibility, and subjects' acceptance of enhanced deep-inspiration breath hold (eDIBH) with high-frequency percussive ventilation (HFPV) by MRI assessment within 1 month. Methods: Twenty-one healthy subjects (12 males/9 females; age: 49.5 ± 5.8 years; BMI: 24.7 ± 3.3 kg/m-2) performed two 1.5 T MRI scans in four visits at weekly intervals under eDIBH and HFPV conditions, accompanied by daily, home-based breath-hold training and spirometric assessments over a 3-week period. eDIBH consisted of 8-min 100% O2 breathing (3 min resting ventilation, 5 min controlled hyperventilation) prior to breath hold. HFPV was set at 200-250 pulses min-1 and 0.8-1.2 bar. Subjects' acceptance and preference were evaluated by questionnaire. To quantify inter- and intrafractional changes, a lung distance metric representing lung topography was computed for 10 reference points: a motion-invariant spinal cord and nine lung structure contours (LSCs: apex, carina, diaphragm, and six vessels as tumor surrogates distributed equally across the lung). To parameterize individual LSC localizability, measures of their spatial variabilities were introduced and lung volumes calculated by automated MRI analysis. Results: eDIBH increased breath-hold duration by > 100% up to 173 ± 73 s at visit 1, and to 217 ± 67 s after 3 weeks of home-based training at visit 4 (p < 0.001). Measures of vital capacity and lung volume remained constant over the 3-week period. Two vessels in the lower lung segment and the diaphragm yielded a two- to threefold improved positional stability with eDIBH, whereby absolute distance variability was significantly smaller for five LSCs; ≥70% of subjects showed significantly better intrafractional lung motion mitigation under reproducible conditions with eDIBH compared with HFPV with smaller ranges most apparent in the anterior-posterior and cranial-caudal directions. Approximately 80% of subjects preferred eDIBH over HFPV, with "less discomfort" named as most frequent reason. Conclusions: Both, eDIBH, and HFPV were well-tolerated. eDIBH duration was long enough to allow for potential PRT. Variability in lung volume was smaller and position of lung structures more precise with eDIBH. Subjects preferred eDIBH over HFPV. Thus, eDIBH is a very promising tool for lung tumor therapy with PRT, and further investigation of its applicability in patients is warranted.

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.

Acute exercise-induced glycocalyx shedding does not differ between exercise modalities, but is associated with total antioxidative capacity.

OBJECTIVES: Regular physical exercise is known to protect endothelial integrity. It has been proposed that acute exercise-induced changes of the (anti-)oxidative system influence early (glycocalyx shedding) and sustained endothelial activation (shedding of endothelial cells, ECs) as well as endothelial-cell repair by circulating hematopoietic stem and progenitor cells (HPCs). However, results are not conclusive and data in trained participants performing different exercise modalities is lacking. DESIGN: Eighteen healthy, well-trained participants (9 runners, 9 cyclists; age: 29.7 ±â€¯4.2 yrs) performed a strenuous acute exercise session consisting of 4 bouts of 4-min high-intensity with decreasing power profile and 3-min low-intensity in-between. METHODS: Average power/speed of intense phases was 85% of the peak achieved in a previous incremental test. Before and shortly after exercise, total oxidative and antioxidative capacities (TAC), shedding of syndecan-1, heparan sulfate, hyaluronan, ECs, and circulating HPCs were investigated. RESULTS: TAC decreased from 1.81 ±â€¯0.42 nmol/L to 1.47 ±â€¯0.23 nmol/L post-exercise (p = 0.010) only in runners. Exercise-induced early and sustained endothelial activation were enhanced post-exercise- syndecan-1: 103.2 ±â€¯63.3 ng/mL to 111.3 ±â€¯71.3 ng/mL, heparan sulfate: from 2637.9 ±â€¯800.1 ng/mL to 3197.1 ±â€¯1416.3 ng/mL, both p < 0.05; hyaluronan: 84.3 ±â€¯21.8 ng/mL to 121.4 ±â€¯29.4 ng/mL, ECs: from 6.6 ±â€¯4.5 cells/µL to 9.5 ±â€¯6.2 cells/µL, both p < 0.01; results were not different between exercise modalities and negatively related to TAC concentrations post-exercise. HPC proportions and self-renewal ability were negatively, while EC concentrations were positively associated with circulating hyaluronan concentrations. CONCLUSIONS: These results highlight the importance of the antioxidative system to prevent the endothelium from acute exercise-induced vascular injury - independent of exercise modality - in well-trained participants. Endothelial-cell repair is associated with hyluronan signaling, possibly a similar mechanism as in wound repair.

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.

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

Exercise is known to acutely and transiently mobilize precursor cells to the peripheral blood. To date, the underlying mechanisms have not yet been fully elucidated and we hypothesized that exercise-induced oxidative stress could be a mobilizing agent, either directly or via circulating apoptotic cells as mediators. The aim of the study was to assess the effect of acute exercise-induced oxidative stress on numbers of circulating angiogenic precursor cells (CACs), circulating non-angiogenic precursor cells (nCACs), mesenchymal precursor cells (MPCs), mature endothelial cells (ECs), and mononuclear cells (MNCs), as well as their apoptotic subsets. Healthy, young males (n = 18, age: 24.2 ± 3.5 years) completed two identical, standardized incremental cycling tests. The first, un-supplemented control test was followed by a 7-day-long supplementation of vitamin C (1,000 mg/day) and E (400 I.U./day), immediately preceding the second test. Blood samples were collected before, directly after, 30, 90, 180, and 270 min after exercise, and aforementioned circulating cell numbers were determined by flow cytometry and a hematology analyzer. Additionally, total oxidative capacity (TOC) and total antioxidative capacity (TAC) were measured in serum at all timepoints. Antioxidative supplementation abolished the exercise-induced increase in the oxidative stress index (TOC/TAC), and reduced baseline concentrations of TOC and TOC/TAC. However, it did not have any effect on CACs, nCACs, and MPC numbers or the increase in apoptotic MNCs following exercise. Our results indicate that exercise-induced oxidative stress is neither a main driver of lymphocyte and monocyte apoptosis, nor one of the mechanisms involved in the immediate or delayed mobilization of precursor cells.

A Single 60.000 IU Dose of Erythropoietin Does Not Improve Short-Term Aerobic Exercise Performance in Healthy Subjects: A Randomized, Double-Blind, Placebo-Controlled Crossover Trial.

Erythropoietin (EPO) boosts exercise performance through increase in oxygen transport capacity following regular administration of EPO but preclinical study results suggest that single high dose of EPO also may improve exercise capacity. Twenty-nine healthy subjects (14 males/15 females; age: 25 ± 3 years) were included in a randomized, double-blind, placebo-controlled crossover study to assess peak work load and cardiopulmonary variables during submaximal and maximal cycling tests following a single dose of 60.000 IU of recombinant erythropoietin (EPO) or placebo (PLA). Submaximal exercise at 40%/60% of peak work load revealed no main effect of EPO on oxygen uptake (27.9 ± 8.7 ml min-1⋅kg-1/ 37.1 ± 13.2 ml min-1⋅kg-1) versus PLA (25.2 ± 3.7 ml min-1⋅kg-1/ 33.1 ± 5.3 ml min-1⋅kg-1) condition (p = 0.447/p = 0.756). During maximal exercise peak work load (PLA: 3.5 ± 0.6 W⋅kg-1 vs. EPO: 3.5 ± 0.6 W kg-1, p = 0.892) and peak oxygen uptake (PLA: 45.1 ± 10.4 ml⋅min-1 kg-1 vs. EPO: 46.1 ± 14.2 ml⋅min-1 kg-1, p = 0.344) reached comparable values in the two treatment conditions. Other cardiopulmonary variables (ventilation, cardiac output, heart rate) also reached similar levels in the two treatment conditions. An interaction effect was found between treatment condition and sex resulting in higher peak oxygen consumption (p = 0.048) and ventilation (p = 0.044) in EPO-treated males. In conclusion, in a carefully conducted study using placebo-controlled design the present data failed to support the hypothesis that a single high dose of EPO has a measurable impact on work capacity in healthy subjects.