Continuous exercise induces airway epithelium damage while a matched-intensity and volume intermittent exercise does not

Epithelial barrier theory in the context of nutrition and environmental exposure in athletes

Exposure to toxic substances, introduced into our daily lives during industrialization and modernization, can disrupt the epithelial barriers in the skin, respiratory, and gastrointestinal systems, leading to microbial dysbiosis and inflammation. Athletes and physically active individuals are at increased risk of exposure to agents that damage the epithelial barriers and microbiome, and their extreme physical exercise exerts stress on many organs, resulting in tissue damage and inflammation. Epithelial barrier-damaging substances include surfactants and enzymes in cleaning products, laundry and dishwasher detergents, chlorine in swimming pools, microplastics, air pollutants such as ozone, particulate matter, and diesel exhaust. Athletes' high-calorie diet often relies on processed foods that may contain food emulsifiers and other additives that may cause epithelial barrier dysfunction and microbial dysbiosis. The type of the material used in the sport equipment and clothing and their extensive exposure may increase the inflammatory effects. Excessive travel-related stress, sleep disturbances and different food and microbe exposure may represent additional factors. Here, we review the detrimental impact of toxic agents on epithelial barriers and microbiome; bring a new perspective on the factors affecting the health and performance of athletes and physically active individuals.

Effects of constant-load exercise and high-intensity interval training on reliever medication consumption and peak expiratory flow in individuals with asthma: a randomised controlled trial

Introduction

The effect of aerobic training on reliever medication consumption (short-acting β2-agonist (SABA)) and peak expiratory flow (PEF) in participants with asthma is poorly known. The comparison between constant-load exercise (CLE) and high-intensity interval training (HIIT) in these outcomes has never been tested. The purpose of the present study was to compare the effects of CLE or HIIT in SABA consumption and PEF improvement during an exercise programme in subjects with asthma.

Methods

Clinically stable participants were randomised into CLE (n=27; 70-85% of the maximal load (Wmax)) or HIIT (n=28; 80-140% Wmax). The programme lasted 12 weeks (two sessions per week, 40 min per session), and the intensity was based on cardiopulmonary exercise testing (CPET). PEF was assessed before and after each exercise session. SABA was used if PEF was <70%. Clinical control (Asthma Control Questionnaire (ACQ)-6), CPET and aerobic fitness were also assessed before and after the intervention.

Results

Both groups were similar at baseline. CLE and HIIT reduced SABA consumption throughout the intervention (p<0.05). Before training, 14 patients required SABA before exercising, but only one needed it after the intervention. Changes in post-exercise PEF were lower in the CLE group than in the HIIT group (1.6±25.3 versus 10.3±13.7%). Both groups improved aerobic fitness (10.1±12.8% versus 5.7±15.6%) and clinical asthma control; however, only the HIIT group achieved a minimal clinically important difference in the ACQ-6 post-intervention (-0.23±1.06 versus -0.52±0.73 Δ score).

Conclusion

CLE and HIIT reduced SABA consumption; however, only HIIT increased PEF and asthma clinical control after the intervention. These results reinforce the importance of exercise training in moderate-to-severe asthma.

The acute effects of endurance exercise on epithelial integrity of the airways in athletes and non-athletes: A systematic review and meta-analysis

INTRODUCTION

Acute endurance exercise may induce airway epithelium injury. However, the response of epithelial integrity markers of the airways including club cell secretory protein (CC16) and surfactant protein D (SP-D) to endurance exercise have not been systematically reviewed. Therefore, the aim of this systematic review and meta-analysis was to assess the acute effects of endurance exercise on markers of epithelial integrity of the airways (CC16, SP-D and the CC16/SP-D ratio) in athletes and non-athletes.

METHODS

A systematic search was performed utilizing PubMed/Medline, EMBASE, Web of Science, and hand searching bibliographies of retrieved articles through to September 2022. Based on the inclusion criteria, articles with available data about the acute effects of endurance exercise on serum or plasma concentrations of CC16, SP-D and CC16/SP-D ratio in athletes and non-athletes were included. Quality assessment of studies and statistical analysis were conducted via Review Manager 5.4 software.

RESULTS

The search resulted in 908 publications. Finally, thirteen articles were included in the review. Acute endurance exercise resulted in an increase in CC16 (P = 0.0006, n = 13) and CC16/SP-D ratio (P = 0.005, n = 2) whereas SP-D (P = 0.47, n = 3) did not change significantly. Subgroup analysis revealed that the type (P = 0.003), but not the duration of exercise (P = 0.77) or the environmental temperature (P = 0.06) affected the CC16 response to endurance exercise.

CONCLUSIONS

Acute endurance exercise increases CC16 and the CC16/SP-D ratio, as markers of epithelial integrity, but not SP-D in athletes and non-athletes.

Pax7+ Satellite Cells in Human Skeletal Muscle After Exercise: A Systematic Review and Meta-analysis

BACKGROUND

Skeletal muscle has extraordinary regenerative capabilities against challenge, mainly owing to its resident muscle stem cells, commonly identified by Pax7⁺, which expediently donate nuclei to the regenerating multinucleated myofibers. This local reserve of stem cells in damaged muscle tissues is replenished by undifferentiated bone marrow stem cells (CD34⁺) permeating into the surrounding vascular system.

OBJECTIVE

The purpose of the study was to provide a quantitative estimate for the changes in Pax7⁺ muscle stem cells (satellite cells) in humans following an acute bout of exercise until 96 h, in temporal relation to circulating CD34⁺ bone marrow stem cells. A subgroup analysis of age was also performed.

METHODS

Four databases (Web of Science, PubMed, Scopus, and BASE) were used for the literature search until February 2022. Pax7⁺ cells in human skeletal muscle were the primary outcome. Circulating CD34⁺ cells were the secondary outcome. The standardized mean difference (SMD) was calculated using a random-effects meta-analysis. Subgroup analyses were conducted to examine the influence of age, training status, type of exercise, and follow-up time after exercise.

RESULTS

The final search identified 20 studies for Pax7⁺ cells comprising a total of 370 participants between the average age of 21 and 74 years and 26 studies for circulating CD34⁺ bone marrow stem cells comprising 494 participants between the average age of 21 and 67 years. Only one study assessed Pax7⁺ cells immediately after aerobic exercise and showed a 32% reduction in exercising muscle followed by a fast repletion to pre-exercise level within 3 h. A large effect on increasing Pax7⁺ cell content in skeletal muscles was observed 24 h after resistance exercise (SMD = 0.89, p < 0.001). Pax7⁺ cells increased to ~ 50% above pre-exercise level 24-72 h after resistance exercise. For a subgroup analysis of age, a large effect (SMD = 0.81, p < 0.001) was observed on increasing Pax7⁺ cells in exercised muscle among adults aged > 50 years, whereas adults at younger age presented a medium effect (SMD = 0.64, p < 0.001). Both resistance exercise and aerobic exercise showed a medium overall effect in increasing circulating CD34⁺ cells (SMD = 0.53, p < 0.001), which declined quickly to the pre-exercise baseline level after exercise within 6 h.

CONCLUSIONS

An immediate depletion of Pax7⁺ cells in exercising skeletal muscle concurrent with a transient release of CD34⁺ cells suggest a replenishment of the local stem cell reserve from bone marrow. A protracted Pax7⁺ cell expansion in the muscle can be observed during 24-72 h after resistance exercise. This result provides a scientific basis for exercise recommendations on weekly cycles allowing for adequate recovery time. Exercise-induced Pax7⁺ cell expansion in muscle remains significant at higher age, despite a lower stem cell reserve after age 50 years. More studies are required to confirm whether Pax7⁺ cell increment can occur after aerobic exercise.

CLINICAL TRIAL REGISTRATION

Registered at the International Prospective Register of Systematic Reviews (PROSPERO) [identification code CRD42021265457].

Exercise sustains the hallmarks of health

Exercise has long been known for its active role in improving physical fitness and sustaining health. Regular moderate-intensity exercise improves all aspects of human health and is widely accepted as a preventative and therapeutic strategy for various diseases. It is well-documented that exercise maintains and restores homeostasis at the organismal, tissue, cellular, and molecular levels to stimulate positive physiological adaptations that consequently protect against various pathological conditions. Here we mainly summarize how moderate-intensity exercise affects the major hallmarks of health, including the integrity of barriers, containment of local perturbations, recycling and turnover, integration of circuitries, rhythmic oscillations, homeostatic resilience, hormetic regulation, as well as repair and regeneration. Furthermore, we summarize the current understanding of the mechanisms responsible for beneficial adaptations in response to exercise. This review aimed at providing a comprehensive summary of the vital biological mechanisms through which moderate-intensity exercise maintains health and opens a window for its application in other health interventions. We hope that continuing investigation in this field will further increase our understanding of the processes involved in the positive role of moderate-intensity exercise and thus get us closer to the identification of new therapeutics that improve quality of life.

Influence of exercise duration on respiratory function and systemic immunity among healthy, endurance-trained participants exercising in sub-zero conditions

Background

Strenuous endurance exercise in sub-zero temperatures can cause airway damage that may lead to EIB. Prolonged exercise can also elicit greater immune perturbations than short-duration exercise. However, the influence of exercise duration on lung function and systemic immunity in sub-zero temperatures has not been established. Additionally, it is currently unknown whether atopic disposition, which is risk factor for EIB, influences respiratory responses in a sub-zero climate. The aim of this study was to compare respiratory and systemic immune responses to two cold air running trials of short and long duration, as well as to examine whether the responses differed between atopic and non-atopic subjects.

Methods

Eighteen healthy, endurance-trained subjects (males/females: 14/4; age: 29.4 ± 5.9 years old; BMI: 23.1 ± 1.7; atopic/non-atopic: 10/8) completed two moderate-intensity climate chamber running trials at − 15 °C, lasting 30 and 90 min, in a randomized, cross-over design. Lung function (spirometry and impulse oscillometry), serum CC16, respiratory symptoms, and blood leukocyte counts were examined before and after the trials.

Results

Lung function was not significantly affected by exercise or exercise duration. CC16 concentration increased after both trials (p = 0.027), but the response did not differ between trials. Respiratory symptom intensity was similar after each trial. There was a greater increase in neutrophils (p < 0.001), and a decrease in eosinophils (p < 0.001) after the 90-min bout. The 90-min protocol increased X5 compared to the 30-min protocol only in atopic subjects (p = 0.015) while atopy increased lower airway symptoms immediately after the 90-min session (p = 0.004).

Conclusions

Our results suggest that a 90-min bout of moderate-intensity exercise at − 15 °C does not cause substantial lung function decrements, airway epithelial damage or respiratory symptoms compared to 30 min running in the same environment, despite a heightened redistribution of white blood cells. However, exercise at − 15 °C may cause airway injury and evoke respiratory symptoms, even at moderate intensity. Atopic status may lead to greater peripheral bronchodilation and higher frequency of respiratory symptoms after long-duration exercise in cold.

Trial registration: 01/02/2022 ISRCTN13977758. This trial was retrospectively registered upon submission to satisfy journal guidelines. The authors had not initially registered the study, as the intervention was considered to be a controlled simulation of exercise in a naturally occurring environment (i.e. sub-zero air) for healthy volunteers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02029-2.

SP-D and CC-16 Pneumoproteins' Kinetics and Their Predictive Role During SARS-CoV-2 Infection

Background

Surfactant protein D (SP-D) and pulmonary club cell protein 16 (CC-16) are called “pneumoproteins” and are involved in host defense against oxidative stress, inflammation, and viral outbreak. This study aimed to determine the predictive value of these pneumoproteins on the incidence of acute respiratory distress syndrome (ARDS) or death in patients with coronavirus disease-2019 (COVID-19).

Methods

This retrospective study included 87 patients admitted to an emergency department. Blood samples were collected on three time points (days 1, 5, and 14 from hospital admission). SP-D and CC-16 serum levels were determined, and univariate and multivariate analyses considering confounding variables (age, body mass index, tobacco use, dyspnea, hypertension, diabetes mellitus, neutrophil-to-lymphocyte ratio) were performed.

Results

Based on the multivariate analysis, SP-D level on D1 was positively and slightly correlated with subsequent development of ARDS, independent of body mass index, dyspnea, and diabetes mellitus. CC-16 level on D1 was modestly and positively correlated with fatal outcome. A rise in SP-D between D1 and D5 and D1 and D14 had a strong negative association with incidence of ARDS. These associations were independent of tobacco use and neutrophil-to-lymphocyte ratio.

Conclusions

Overall, our data reveal that increase in SP-D levels is a good prognostic factor for patients with COVID-19, and that initial CC-16 levels correlated with slightly higher risk of death. SP-D and CC-16 may prove useful to predict outcomes in patients with COVID-19.

Is airway damage during physical exercise related to airway dehydration? Inputs from a computational model

In healthy subjects, at low minute ventilation (V̇_E) during physical exercise, the water content and the temperature of the airways are well regulated. However, with the increase in V̇_E, the bronchial mucosa becomes dehydrated and epithelial damage occurs. Our goal was to demonstrate the correspondence between the ventilatory threshold inducing epithelial damage, measured experimentally, and the dehydration threshold, estimated numerically. In 16 healthy adults, we assessed epithelial damage before and following a 30-min continuous cycling exercise at 70% of maximal work rate, by measuring the variation pre- to post-exercise of serum club cell protein (cc16/cr). Blood samples were collected at rest, just at the end of the standardized 10-min warm-up, and immediately, 30 min and 60 min post-exercise. V̇_E was measured continuously during exercise. Airway water and heat losses were estimated using a computational model adapted to the experimental conditions and were compared to a literature-based threshold of dehydration. Eleven participants exceeded the threshold for bronchial dehydration during exercise (group A) and 5 did not (group B). Compared to post warm-up, the increase in cc16/cr post-exercise was significant (mean increase ± SEM: 0.48 ± 0.08 ng.l^-1, i.e. 101 ± 32%, p < 0.001) only in group A but not in group B (mean difference ± SEM: 0.10 ± 0.04 ng.l^-1, i.e. 13 ± 7 %, p = 0.79). Our findings suggest that the use of a computational model may be helpful to estimate an individual dehydration threshold of the airways that is associated with epithelial damage during physical exercise.

Comparison of heart rates at fixed percentages and the ventilatory thresholds in patients with interstitial lung disease

Heart rate (HR) responses to maximal exercise are commonly used for the prescription of training intensities in pulmonary rehabilitation. Those intensities are usually based on fixed percentages of peak HR (HRpeak), heart rate reserve (HRR), or peak work load (Wpeak), and rarely on HRs at the individual ventilatory thresholds (VT1 and VT2) derived from cardiopulmonary exercise testing (CPET). For patients suffering from interstitial lung disease (ILD), data on cardiorespiratory responses to CPET are scarce. Thus, the aim of this study was to record cardiorespiratory responses to CPET and to compare fixed HR percentages with HRs at VT1 and VT2 in ILD patients. A total of 120 subjects, 80 ILD patients and 40 healthy controls, underwent a symptom‐limited CPET. From the ILD patient, 32 suffered from idiopathic pulmonary fibrosis (IPF), 37 from connective tissue disease (CTD), and 11 from sarcoidosis. HRs at fixed percentages, that is, at 70%HRpeak, at 70%Wpeak, and at 60%HRR were significantly lower in the ILD patients compared with the control group (p‐values: 0.001, 0.044, and 0.011). Large percentages of HR values at 70%Wpeak and 60%HRR ranged between the HRs at VT1 and VT2 in ILD subgroups and controls as well. HRs at 70%HRpeak were lower than HRs at VT1 in 66% of the IPF patients, 54% of the CTD patients, and 55% of patients with sarcoidosis compared with 18% in the control group. Our findings demonstrate a considerable scattering of fixed HR percentages compared with HRs at the individual VTs derived from CPET in ILD patients. These findings may provide valuable information for the prescription of exercise intensity in pulmonary rehabilitation of ILD patients.

The active grandparent hypothesis: Physical activity and the evolution of extended human healthspans and lifespans

The proximate mechanisms by which physical activity (PA) slows senescence and decreases morbidity and mortality have been extensively documented. However, we lack an ultimate, evolutionary explanation for why lifelong PA, particularly during middle and older age, promotes health. As the growing worldwide epidemic of physical inactivity accelerates the prevalence of noncommunicable diseases among aging populations, integrating evolutionary and biomedical perspectives can foster new insights into how and why lifelong PA helps preserve health and extend lifespans. Building on previous life-history research, we assess the evidence that humans were selected not just to live several decades after they cease reproducing but also to be moderately physically active during those postreproductive years. We next review the longstanding hypothesis that PA promotes health by allocating energy away from potentially harmful overinvestments in fat storage and reproductive tissues and propose the novel hypothesis that PA also stimulates energy allocation toward repair and maintenance processes. We hypothesize that selection in humans for lifelong PA, including during postreproductive years to provision offspring, promoted selection for both energy allocation pathways which synergistically slow senescence and reduce vulnerability to many forms of chronic diseases. As a result, extended human healthspans and lifespans are both a cause and an effect of habitual PA, helping explain why lack of lifelong PA in humans can increase disease risk and reduce longevity.

Exercise duration modulates upper and lower respiratory fluid cellularity, antiviral activity, and lung gene expression

Exercise has substantial health benefits, but the effects of exercise on immune status and susceptibility to respiratory infections are less clear. Furthermore, there is limited research examining the effects of prolonged exercise on local respiratory immunity and antiviral activity. To assess the upper respiratory tract in response to exercise, we collected nasal lavage fluid (NALF) from human subjects (1) at rest, (2) after 45 min of moderate-intensity exercise, and (3) after 180 min of moderate-intensity exercise. To assess immune responses of the lower respiratory tract, we utilized a murine model to examine the effect of exercise duration on bronchoalveolar lavage (BAL) fluid immune cell content and lung gene expression. NALF cell counts did not change after 45 min of exercise, whereas 180 min significantly increased total cells and leukocytes in NALF. Importantly, fold change in NALF leukocytes correlated with the post-exercise fatigue rating in the 180-min exercise condition. The acellular portion of NALF contained strong antiviral activity against Influenza A in both resting and exercise paradigms. In mice undergoing moderate-intensity exercise, BAL total cells and neutrophils decreased in response to 45 or 90 min of exercise. In lung lobes, increased expression of heat shock proteins suggested that cellular stress occurred in response to exercise. However, a broad upregulation of inflammatory genes was not observed, even at 180 min of exercise. This work demonstrates that exercise duration differentially alters the cellularity of respiratory tract fluids, antiviral activity, and gene expression. These changes in local mucosal immunity may influence resistance to respiratory viruses, including influenza or possibly other pathogens in which nasal mucosa plays a protective role, such as rhinovirus or SARS-CoV-2.

The interaction effect of aerobic exercise and vitamin D supplementation on inflammatory factors, anti-inflammatory proteins, and lung function in male smokers: a randomized controlled trial

Background

This study aimed to investigate the interaction effect of aerobic exercise and vitamin D supplementation on inflammation (TNF-α, IL-6, CC16, SP-D, and CC16/SP-D ratio) and lung function (FEV₁, FVC, and FEV₁/FVC ratio) in male smokers.

Methods

After applying inclusion criteria, a total of 40 healthy male smokers were recruited in this study. The participants were randomly divided into four groups as follows: Aerobic Exercise + vitamin D Supplementation (AE + VitD, n = 10), Aerobic Exercise (AE, n = 10), vitamin D Supplementation (VitD, n = 10), and Control (C, n = 10). The participants in the AE + VitD and AE groups performed aerobic exercise training (running) up to 50% of the maximum heart rate, three times a week for four weeks. Participants in AE + VitD and VitD groups received 6000 IU/w vitamin D₃ for four weeks. The participants in control group did not receive any intervention. Serum tumor necrosis factor (TNF)-α, interleukin (IL)-6, Clara cell protein (CC16), surfactant protein (SP)-D, CC16/SP-D ratio, and lung function (FEV1, FVC, and FEV1/FVC ratio) were measured before and after four weeks of intervention.

Results

Serum levels of TNF-α, IL-6, and CC16 decreased significantly in AE + VitD, VitD, and AE groups after four weeks (P < 0.05). Serum SP-D level decreased significantly only in the AE + VitD group (P = 0.011). In addition, FEV1 and FVC increased significantly (P < 0.05) in AE + VitD and AE groups after four weeks of intervention. However, the interventions did not have a significant effect on CC16/SP-D ratio and FEV1/FVC ratio (P > 0.05). Furthermore, serum levels of 1,25-dihydroxyvitamin D increased significantly in AE + VitD and VitD groups (P < 0.05) after four weeks of intervention. However, except for TNF-α, between-group comparisons showed no significant differences in levels of IL-6, CC16, SP-D, CC16/SP-D ratio, FEV1, FVC, FEV1/FVC, and 1,25-dihydroxyvitamin D (P > 0.05).

Conclusions

The results of present study were that aerobic exercise combined with vitamin D supplementation can reduce serum inflammatory factors and anti-inflammatory proteins and improve lung function after four weeks of intervention. Further trials with larger sample size and longer duration are suggested to confirm these results.

Trial registration Retrospectively registered. IRCT20180513039637N4. Registration date: 2020/10/20. URL: https://www.irct.ir/search/result?query=IRCT20180513039637N4

Scientific Challenges on Theory of Fat Burning by Exercise

Exercise training decreases abdominal fat in an intensity-dependent manner. The fat loss effect of exercise has been intuitively thought to result from increased fat burning during and after exercise, defined by conversion of fatty acid into carbon dioxide in consumption of oxygen. Nevertheless, increasing exercise intensity decreases oxidation of fatty acids derived from adipose tissue despite elevated lipolysis. The unchanged 24-h fatty acid oxidation during and after exercise does not provide support to the causality between fat burning and fat loss. In this review, alternative perspectives to explain the fat loss outcome are discussed. In brief, carbon and nitrogen redistribution to challenged tissues (muscle and lungs) for fuel replenishment and cell regeneration against abdominal adipose tissue seems to be the fundamental mechanism underlying the intensity-dependent fat loss effect of exercise. The magnitude of lipolysis (fatty acid release from adipocytes) and the amount of post-meal carbon and nitrogen returning to abdominal adipose tissue determines the final fat tissue mass. Therefore, meal arrangement at the time when muscle has the greatest reconstruction demand for carbon and nitrogen could decrease abdominal fat accumulation while increasing muscle mass and tissue repair.

Comprehensive Analysis of Heat and Water Exchanges in the Human Lungs

This work presents a new mathematical model of the heat and water exchanges in the human lungs (newborn to adult). This model is based on a local description of the water and energy transports in both the lumen and the surrounding tissues, and is presented in a comprehensive, dimensionless framework with explicitly stated assumptions and a strong physiological background. The model is first used to analyze and quantify the key phenomena and dimensionless numbers governing these heat and water exchanges and then it is applied to an adult in various situations (varying atmospheric conditions, exercising…). The results highlight several interesting physiological elements. They show that the bronchial region of the lungs is able to condition the air in all the considered situations even if, sometimes, for instance when exercising, distal generations have to be involved. The model also shows that these distal generations are super-conditioners. Moreover, the results quantify the key role of the submucosal glands in mucus hydration. They also show that, during expiration, a significant cooling of the air and condensation of water occur along the respiratory tract as the vascularization of the tissues surrounding the airways is not able to maintain these tissues at body temperature during inspiration. Due to the interaction between several phenomena, it appears that the ratio of the amount of water returned to the mucosa during expiration to the amount extracted during inspiration is almost independent of the breathing conditions (around 33%). The results also show that, in acute situations, such as suffering from a pathology with airway dysfunction, when being intubated or when exercising above an intensity threshold, the heat and water exchanges in the lungs may be critical regarding mucus hydration. In proximal generations, the evaporation may overwhelm the ability of the submucosal glands to replenish the airway surface liquid with water. In some situations, the cooling of the mucosa may be very important; it can even become colder than the inspired air, due to evaporative cooling. Finally, the results show that breathing cold air can significantly increase the exchanges between the lungs and the environment, which can be critical regarding disease transmission.