Oxygen cost of exercise hyperpnoea is greater in women compared with men

The metabolic cost of breathing for exercise ventilations: effects of age and sex

Given that there are both sex-based structural differences in the respiratory system and age-associated declines in pulmonary function, the purpose of this study was to assess the effects of age and sex on the metabolic cost of breathing (V̇o2RM) for exercise ventilations in healthy younger and older males and females. Forty healthy participants (10 young males 24 ± 3 yr; 10 young females 24 ± 3 yr; 10 older males 63 ± 3 yr, 10 older females 63 ± 6 yr) mimicked their exercise breathing patterns (voluntary hyperpnea) in the absence of exercise across a range of exercise intensities. At peak exercise, V̇o2RM represented a significantly greater fraction of peak oxygen consumption (V̇o2peak) in young females, 12.7 ± 4.0%, compared with young males, 10.7 ± 3.0% (P = 0.027), whereas V̇o2RM represented 13.5 ± 2.3% of V̇o2peak in older females and 13.2 ± 3.3% in older males. At relative ventilations, there was a main effect of age, with older males consuming a significantly greater fraction of V̇o2RM (6.6 ± 1.9%) than the younger males (4.4 ± 1.3%; P = 0.012), and older females consuming a significantly greater fraction of V̇o2RM (6.9 ± 2.5%) than the younger females (5.1 ± 1.4%; P = 0.004) at 65% V̇emax. Furthermore, both younger and older males had significantly better respiratory muscle efficiency than their female counterparts at peak exercise (P = 0.011; P = 0.015). Similarly, younger participants were significantly more efficient than older participants (6.5 ± 1.5% vs. 5.5 ± 2.0%; P = 0.001). Normal age-related changes in respiratory function, in addition to sex-based differences in airway anatomy, appear to influence the ventilatory responses and the cost incurred to breathe during exercise.NEW & NOTEWORTHY Here we show that at moderate and high-intensity exercise, older individuals incur a higher cost to breathe than their younger counterparts. However, as individuals age, the sex difference in the cost of breathing narrows. Collectively, our findings suggest that the normative age-related changes in respiratory structure and function, and sex differences in airway anatomy, appear to influence the ventilatory responses to exercise and the oxygen cost to breathe.

Effect of Inspiratory Muscle-Loaded Exercise Training on Ventilatory Response and Intercostal Muscle Deoxygenation During Incremental Cycling Exercise

Purpose: This study evaluated the effects of exercise training (ET) and inspiratory muscle-loaded exercise training (IMLET) on ventilatory response and intercostal muscle deoxygenation levels during incremental cycling exercise. Methods: Twenty-one male participants were randomly divided into IMLET (n = 10) or ET (n = 11) groups. All participants underwent a 4-week cycling exercise training at 60% peak oxygen uptake. IMLET loaded 50% of maximal inspiratory pressure (PImax). Respiratory muscle strength test, respiratory muscle endurance test (RMET), resting hypoxic ventilatory responsiveness (HVR) test, and incremental cycling test were performed pre- and post-training. Results: The extent of improvement in the PImax was significantly greater in the IMLET group (24%) than in the ET group (8%) (p = .018), and an extended RMET time was observed in the IMLET group (p < .001). Minute ventilation (V ˙ E ) during exercise was unchanged in both groups before and after training, but tidal volume during exercise increased in the IMLET group. The increase in the exercise intensity threshold for muscle deoxygenation was similar in both groups (p < .001). HVR remained unchanged in both groups post-training. The exercise duration for the incremental exercise until reaching fatigue increased by 7.9% after ET and 6.9% after IMLET (p < .001). Conclusion: The 4-week IMLET improved respiratory muscle strength and endurance but did not alter HVR. Respiratory muscle deoxygenation was alleviated by exercise training, with a limited impact of inspiratory load training.

The pulmonary physiology of exercise

The pulmonary system is the first and last "line of defense" in terms of maintaining blood gas homeostasis during exercise. Our review provides the reader with an overview of how the pulmonary system responds to acute exercise. We undertook this endeavor to provide a companion article to "Cardiovascular Response to Exercise," which was published in Advances in Physiological Education. Together, these articles provide the readers with a solid foundation of the cardiopulmonary response to acute exercise in healthy individuals. The intended audience of this review is level undergraduate or graduate students and/or instructors for such classes. By intention, we intend this to be used as an educational resource and seek to provide illustrative examples to reinforce topics as well as highlight uncertainty to encourage the reader to think "beyond the textbook." Our treatment of the topic presents "classic" concepts along with new information on the pulmonary physiology of healthy aging.NEW & NOTEWORTHY Our narrative review is written with the student of the pulmonary physiology of exercise in mind, be it a senior undergraduate or graduate student or those simply refreshing their knowledge. We also aim to provide examples where the reader can incorporate real scenarios.

Dysanapsis is not associated with exertional dyspnoea in healthy male and female never-smokers aged 40 years and older

In healthy adults, airway-to-lung (i.e., dysanapsis) ratio is lower and dyspnoea during exercise at a given minute ventilation (V̇E) is higher in females than in males. We investigated the relationship between dysanapsis and sex on exertional dyspnoea in healthy adults. We hypothesized that females would have a smaller airway-to-lung ratio than males and that exertional dyspnoea would be associated with airway-to-lung ratio in males and females. We analyzed data from n = 100 healthy never-smokers aged ≥40 years enrolled in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study who underwent pulmonary function testing, a chest computed tomography scan, and cardiopulmonary exercise testing. The luminal area of the trachea, right main bronchus, left main bronchus, right upper lobe, bronchus intermedius, left upper lobe, and left lower lobe were 22%-37% smaller (all p < 0.001) and the airway-to-lung ratio (i.e., average large conducting airway diameter relative to total lung capacity) was lower in females than in males (0.609 ± 0.070 vs. 0.674 ± 0.082; p < 0.001). During exercise, there was a significant effect of V̇E, sex, and their interaction on dyspnoea (all p < 0.05), indicating that dyspnoea increased as a function of V̇E to a greater extent in females than in males. However, after adjusting for age and total lung capacity, there were no significant associations between airway-to-lung ratio and measures of exertional dyspnoea, regardless of sex (all r < 0.34; all p > 0.05). Our findings suggest that sex differences in airway size do not contribute to sex differences in exertional dyspnoea.

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

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

Impact of high-intensity interval hyperpnea on aerobic energy release and inspiratory muscle fatigue

Respiratory muscle endurance training reportedly has beneficial effects on whole-body endurance performance. We produced a novel high-intensity interval (HII) protocol and characterized the associated physiological responses and respiratory muscle fatigue. Peak oxygen uptake of respiratory muscle (V̇O2peakRM) was estimated during the respiratory incremental test. The HII session consisted of five 3-minute hyperpnea periods at 100%V̇O2peakRM interspersed with 2-minute periods at 40%V̇O2peakRM (25 min total). The high-intensity continuous (HIC) session involved a single time-to-end bout of hyperpnea at 100%V̇O2peakRM. The moderate-intensity continuous (MIC) session involved 25 min of hyperpnea at 60% of maximal voluntary ventilation. V̇O2RM was recorded continuously, and maximal inspiratory pressure (PImax) was assessed before and after the sessions. HII session: V̇O2RM gradually increased as the sets proceeded, whereas PImax decreased significantly. HIC session: V̇O2RM increased progressively, and the time to end was 6.5 ± 0.5 min. PImax decreased significantly. MIC session: V̇O2RM did not change for 25 min, and PImax remained unchanged. The duration of V̇O2RM at near- and supra-maximal levels in the HII session (10 ± 1 min) was longer than that in the HIC session (4 ± 1 min). The decrease in PImax was larger in the HII session (-12 ± 3 %) than MIC session (-4 ± 3 %). The HII protocol is characterized by a longer time to maximally stimulate the aerobic energy system of respiratory muscle than the HIC protocol and greater inspiratory muscle fatigue than the traditional MIC protocol. These results suggest that the HII protocol could enhance the efficacy of respiratory muscle training programs.

Is the Lung Built for Exercise? Advances and Unresolved Questions

ABSTRACT

Nearly 40 yr ago, Professor Dempsey delivered the 1985 ACSM Joseph B. Wolffe Memorial Lecture titled: "Is the lung built for exercise?" Since then, much experimental work has been directed at enhancing our understanding of the functional capacity of the respiratory system by applying complex methodologies to the study of exercise. This review summarizes a symposium entitled: "Revisiting 'Is the lung built for exercise?'" presented at the 2022 American College of Sports Medicine annual meeting, highlighting the progress made in the last three-plus decades and acknowledging new research questions that have arisen. We have chosen to subdivide our topic into four areas of active study: (i) the adaptability of lung structure to exercise training, (ii) the utilization of airway imaging to better understand how airway anatomy relates to exercising lung mechanics, (iii) measurement techniques of pulmonary gas exchange and their importance, and (iv) the interactions of the respiratory and cardiovascular system during exercise. Each of the four sections highlights gaps in our knowledge of the exercising lung. Addressing these areas that would benefit from further study will help us comprehend the intricacies of the lung that allow it to meet and adapt to the acute and chronic demands of exercise in health, aging, and disease.

Attenuating intrathoracic pressure swings decreases cardiac output at different intensities of exercise

Intrathoracic pressure (ITP) swings that permit spontaneous ventilation have physiological implications for the heart. We sought to determine the effect of respiration on cardiac output (Q ̇ $\dot Q$ ) during semi-supine cycle exercise using a proportional assist ventilator to minimize ITP changes and lower the work of breathing (Wb ). Twenty-four participants (12 females) completed three exercise trials at 30%, 60% and 80% peak power (Wmax ) with unloaded (using a proportional assist ventilator, PAV) and spontaneous breathing. Intrathoracic and intraabdominal pressures were measured with balloon catheters placed in the oesophagus and stomach. Left ventricular (LV) volumes andQ ̇ $\dot Q$ were determined via echocardiography. Heart rate (HR) was measured with electrocardiogram and a customized metabolic cart measured oxygen uptake (V ̇ O 2 ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}}}$ ). Oesophageal pressure swings decreased from spontaneous to PAV breathing by -2.8 ± 3.1, -4.9 ± 5.7 and -8.1 ± 7.7 cmH2 O at 30%, 60% and 80% Wmax , respectively (P = 0.01). However, the decreases in Wb were similar across exercise intensities (27 ± 42 vs. 35 ± 24 vs. 41 ± 22%, respectively, P = 0.156). During PAV breathing compared to spontaneous breathing,Q ̇ $\dot Q$ decreased by -1.0 ± 1.3 vs. -1.4 ± 1.4 vs. -1.5 ± 1.9 l min-1 (all P < 0.05) and stroke volume decreased during PAV breathing by -11 ± 12 vs. -9 ± 10 vs. -7 ± 11 ml from spontaneous breathing at 30%, 60% and 80% Wmax , respectively (all P < 0.05). HR was lower during PAV breathing by -5 ± 4 beats min-1 at 80% Wmax (P < 0.0001). Oxygen uptake decreased by 100 ml min-1 during PAV breathing compared to spontaneous breathing at 80% Wmax (P < 0.0001). Overall, attenuating ITPs mitigated LV preload and ejection, thereby suggesting that the ITPs associated with spontaneous respiration impact cardiac function during exercise. KEY POINTS: Pulmonary ventilation is accomplished by alterations in intrathoracic pressure (ITP), which have physiological implications on the heart and dynamically influence the loading parameters of the heart. Proportional assist ventilation was used to attenuate ITP changes and decrease the work of breathing during exercise to examine its effects on left ventricular (LV) function. Proportional assist ventilation with progressive exercise intensities (30%, 60% and 80% Wmax ) led to reductions in cardiac output at all intensities, primarily through reductions in stroke volume. Decreases in LV end-diastolic volume (30% and 60% Wmax ) and increases in LV end-systolic volume (80% Wmax ) were responsible for the reduction in stroke volume. The relationship between cardiac output and oxygen uptake is disrupted during respiratory muscle unloading.

A Systematic Review of Methods Used to Determine the Work of Breathing during Exercise

INTRODUCTION

Measurement of the work of breathing (Wb) during exercise provides useful insights into the energetics and mechanics of the respiratory muscles across a wide range of minute ventilations. The methods and analytical procedures used to calculate the Wb during exercise have yet to be critically appraised in the literature.

PURPOSE

The aim of this systematic review was to evaluate the quality of methods used to measure the Wb during exercise in the available literature.

METHODS

We conducted an extensive search of three databases for studies that measured the Wb during exercise in adult humans. Data were extracted on participant characteristics, flow/volume and pressure devices, esophageal pressure (P oes ) catheters, and methods of Wb analysis.

RESULTS

A total of 120 articles were included. Flow/volume sensors used were primarily pneumotachographs ( n = 85, 70.8%), whereas the most common pressure transducer was of the variable reluctance type ( n = 63, 52.5%). Esophageal pressure was frequently obtained via balloon-tipped catheters ( n = 114, 95.0%). Few studies mentioned calibration, frequency responses, and dynamic compensation of their measurement devices. The most popular method of measuring the Wb was pressure-volume integration ( n = 51, 42.5%), followed by the modified Campbell ( n = 28, 23.3%) and Dean & Visscher diagrams ( n = 26, 21.7%). Over one-third of studies did not report the methods used to process their pressure-volume data, and the majority (60.8%) of studies used the incorrect Wb units and/or failed to discuss the limitations of their Wb measurements.

CONCLUSIONS

The findings of this systematic review highlight the need for the development of a standardized approach for measuring Wb, which is informative, practical, and accessible for future researchers.

The oxygen transport cascade and exercise: Lessons from comparative physiology

Studies of animal physiology not only provide valuable knowledge for the species in question, but also offer insights into human physiology. This thought is best highlighted by the 'Krogh Principle', which states "for many problems there is an animal on which it can be most conveniently studied". This graphical review focuses on three distinct stages of the oxygen transport cascade in which human exercise physiology knowledge has been enhanced by studies carried out in animal models. We begin by exploring ventilation, and the detrimental effects of cold, dry air on the airways in two sets of elite athletes, the cross-country skier and the racing sled dog. We then discuss the transport of oxygen via hemoglobin in humans and deer mice with relatively shifted oxygen dissociation curves. Finally, we consider the technical difficulties of measuring respiratory muscle blood flow in exercising humans and how an equine model can provide an understanding of the distribution of blood flow during exercise. These cases illustrate the complementary nature of physiological studies across species.

Sex matters: the frequently overlooked importance of considering sex in computational models

Personalised medicine and the development of a virtual human or a digital twin comprises visions of the future of medicine. To realise these innovations, an understanding of the biology and physiology of all people are required if we wish to apply these technologies at a population level. Sex differences in health and biology is one aspect that has frequently been overlooked, with young white males being seen as the "average" human being. This has not been helped by the lack of inclusion of female cells and animals in biomedical research and preclinical studies or the historic exclusion, and still low in proportion, of women in clinical trials. However, there are many known differences in health between the sexes across all scales of biology which can manifest in differences in susceptibility to diseases, symptoms in a given disease, and outcomes to a given treatment. Neglecting these important differences in the development of any health technologies could lead to adverse outcomes for both males and females. Here we highlight just some of the sex differences in the cardio-respiratory systems with the goal of raising awareness that these differences exist. We discuss modelling studies that have considered sex differences and touch on how and when to create sex-specific models. Scientific studies should ensure sex differences are included right from the study planning phase and results reported using sex as a biological variable. Computational models must have sex-specific versions to ensure a movement towards personalised medicine is realised.

EXERCISE-INDUCED ARTERIAL HYPOXEMIA IN FEMALE MASTERS ATHTLETES

The purpose of the study was to characterize exercise induced arterial hypoxemia (EIAH) in female masters athletes (FMA). We hypothesized that FMA would experience EIAH during treadmill running. Eight FMA (48-57 years) completed pulmonary function testing and an incremental exercise test until exhaustion (V̇O₂max=45.7±6.5, range:35-54ml/kg/min). On a separate day, the participants were instrumented with a radial arterial catheter and an esophageal temperature probe. Participants performed three to four constant load exercise tests at 60-70, 75, 90, 95, and 100% of maximal oxygen uptake while sampling arterial blood and recording esophageal temperature. We found that FMA decrease their partial pressure of oxygen (86.0±7.6, range:73-108mmHg), arterial saturation (96.2±1.2, range:93-98%), and widen their alveolar to arterial oxygen difference (23.2±8.8, range:5-42mmHg) during all exercise intensities however, with variability in terms of severity and pattern. Our findings suggest that FMA experience EIAH however aerobic fitness appears unrelated to occurrence or severity (r=0.13, p=0.756).

Inspiratory Muscle Training Improves Maximal Inspiratory Pressure Without Increasing Performance in Elite Swimmers

PURPOSE

To analyze the effect of inspiratory muscle training (IMT) on the maximal inspiratory mouth pressure (MIP) and performance of elite swimmers.

METHODS

Eight participants performed a 3000-m swimming test (T-3000), followed by blood lactate measurements at 1 and 5 minutes postexercise.. The testing protocol was carried out before and after 6 weeks of IMT, in which a high-volume IMT group (HV-IMT) (n = 4) performed IMT twice a day-in the morning in a seated position and in the afternoon in a concurrent session of IMT and core muscle training. Also, a low-volume IMT group (LV-IMT) (n = 4) performed IMT in the morning session only.

RESULTS

After the intervention, both groups improved their MIP, HV-IMT (132.75 [27.42] to 156.75 [21.88] cmH2O; P = .010; d = 0.967) and LV-IMT (149.25 [22.82] to 171.50 [23.74] cmH2O; P = .013; d = 0.955), without a significant difference between groups (P = .855). Regarding swimming performance, there were no changes between groups in the T-3000 (P = .472) or lactate removal rate (P = .104).

CONCLUSION

IMT increased inspiratory muscle strength in elite swimmers, but there was no association or meaningful impact on swimming performance.

The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise

NEW FINDINGS

What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

ABSTRACT

We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P < 0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P = 0.151) but was significantly lower during medium (25%, P = 0.02) and high (36%, P < 0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P < 0.05). The EMGdi was significantly lower in medium and high PAV conditions (P = 0.035 and P < 0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r = 0.61, P = 0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

Sex differences in blood pressure and inactive limb blood flow responses during dynamic leg exercise with increased inspiratory muscle work

We hypothesized that, compared with young males, young females have a smaller decrease in blood flow to the inactive limb, accompanied by a smaller increase in arterial blood pressure, during dynamic exercise with increased inspiratory muscle work. Young males and females performed dynamic knee-extension and -flexion exercises for 10 min (spontaneous breathing for 5 min and voluntary hyperpnoea with or without inspiratory resistance for 5 min). Mean arterial blood pressure (MAP) and mean blood flow (MBF) in the brachial artery were continuously measured by means of finger photoplethysmography and Doppler ultrasound, respectively. No sex differences were found in the ΔMAP and ΔMBF (Δ: from baseline) during exercise without inspiratory resistance. In contrast, the ΔMAP during exercise with inspiratory resistive breathing was greater (P < 0.05) in males (+31.3 ± 2.1 mmHg, mean ± SE) than females (+18.9 ± 3.2 mmHg). The MBF during exercise with inspiratory resistance did not change in males (-4.4 ± 10.6 mL/min), whereas it significantly increased in females (+25.2 ± 15.4 mL/min). These results suggest that an attenuated inspiratory muscle-induced metaboreflex in young females affects blood flow distribution during submaximal dynamic leg exercise.

Influence of graded hypercapnia on endurance exercise performance in healthy humans

Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO2). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO2 on 2-mile run performance, as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49 ± 5 mL·kg-1·min-1; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO2. During each trial, participants completed 10 min of walking at ∼40% peak oxygen uptake followed by a self-paced 2-mile treadmill time trial. One participant was unable to complete the 4% CO2 trial due to lightheadedness during the run. Compared with the 0% CO2 trial, run performance was 5 ± 3% and 7 ± 3% slower in the 2% and 4% CO2 trials, respectively (both P < 0.001). Run performance was significantly slower with 4% versus 2% CO2 (P = 0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO2 trial compared with both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO2 impair endurance performance in a stepwise manner in healthy humans.

Physiological impact of load carriage exercise: Current understanding and future research directions

Load carriage (LC) refers to the use of personal protective equipment (PPE) and/or load-bearing apparatus that is mostly worn over the thoracic cavity. A commonplace task across various physically demanding occupational groups, the mass being carried during LC duties can approach the wearer's body mass. When compared to unloaded exercise, LC imposes additional physiological stress that negatively impacts the respiratory system by restricting chest wall movement and altering ventilatory mechanics as well as circulatory responses. Consequently, LC activities accelerate the development of fatigue in the respiratory muscles and reduce exercise performance in occupational tasks. Therefore, understanding the implications of LC and the effects specific factors have on physiological capacities during LC activity are important to the implementation of effective mitigation strategies to ameliorate the detrimental effects of thoracic LC. Accordingly, this review highlights the current physiological understanding of LC activities and outlines the knowledge and efficacy of current interventions and research that have attempted to improve LC performance, whilst also highlighting pertinent knowledge gaps that must be explored via future research activities.

Effects of breathing control using visual feedback of thoracoabdominal movement on aerobic exercise

PURPOSE

To clarify whether voluntary respiratory movement control strategy is sustainable during exercise and to determine its effect on aerobic exercise.

MATERIAL AND METHODS

Ten healthy men were enrolled in this study. We developed a device that can convert information on thoracoabdominal changes from an inductance plethysmograph and display the Konno-Mead diagram on the monitor in real time for each breath. On the first day, an incremental load test (ILT) was performed under two conditions. On the second day, a constant load test (CLT) was performed under two conditions using the load 1 min before the anaerobic threshold (AT).

RESULTS

In the ILT, a significant prolongation of AT time was observed with voluntary respiratory movement control. In the CLT, carbon dioxide excretion showed no significant interaction, but the gas exchange ratio did.

CONCLUSION

Voluntary respiratory movement control using a combination of chest band and visual feedback of thoracoabdominal movements may be a respiratory strategy to enhance aerobic exercise.

Sex differences in the ventilatory responses to exercise in mild-moderate obesity

NEW FINDINGS

What is the central question of the study? What are the sex differences in ventilatory responses during exercise in adults with obesity. What is the main finding and its importance? Tidal volume and expiratory flows are lower in females when compared with males at higher levels of ventilation despite small increases in end-expiratory lung volumes. Since dyspnea on exertion is a frequent complaint, particularly in females with obesity, careful attention should be paid to unpleasant respiratory symptoms and mechanical ventilatory constraints before prescribing exercise.

ABSTRACT

Obesity is associated with altered ventilatory responses, which may be exacerbated in females due to the functional consequences of sex-related morphological differences in the respiratory system. This study examined sex differences in ventilatory responses during exercise in adults with obesity. Healthy adults with obesity (n = 73; 48 females) underwent pulmonary function testing, underwater weighing, magnetic resonance imaging, a graded exercise test to exhaustion, and two constant work rate exercise tests; one at a fixed work rate (60W for females and 105W for males) and one at a relative intensity (50% of peak oxygen uptake, V̇O_2peak ). Metabolic, respiratory, and perceptual responses were assessed during exercise. Compared with males, females used a smaller proportion of their ventilatory capacity at peak exercise (69.13 ± 14.49 vs. 77.41 ± 17.06 % maximum voluntary ventilation, P = 0.0374). Females also utilized a smaller proportion of their forced vital capacity (FVC) at peak exercise (tidal volume: 48.51±9.29 vs. 54.12±10.43 %FVC, P = 0.0218). End-expiratory lung volumes were 2-4% higher in females compared with males during exercise (P<0.05), while end-inspiratory lung volumes were similar. Since the males were initiating inspiration from a lower lung volume, they experienced greater expiratory flow limitation during exercise. Ratings of perceived breathlessness during exercise were similar between females and males at comparable levels of ventilation. In summary, sex differences in the manifestations of obestity-related mechanical ventilatory constraints were observed. Since dyspnea on exertion is a common complaint in patients with obesity, particularly in females, exercise prescriptions should be tailored with the goal of minimizing unpleasant respiratory sensations. This article is protected by copyright. All rights reserved.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

CO2-Enriched Air Inhalation Modulates the Ventilatory and Metabolic Responses of Endurance Runners During Incremental Running in Hypobaric Hypoxia

Cao, Yinhang, Naoto Fujii, Tomomi Fujimoto, Yin-Feng Lai, Takeshi Ogawa, Tsutomu Hiroyama, Yasushi Enomoto, and Takeshi Nishiyasu. CO₂-enriched air inhalation modulates the ventilatory and metabolic responses of endurance runners during incremental running in hypobaric hypoxia. High Alt Med Biol. 23:125-134, 2022. Aim: We measured the effects of breathing CO₂-enriched air on ventilatory and metabolic responses during incremental running exercise under moderately hypobairc hypoxic (HH) conditions. Materials and Methods: Ten young male endurance runners [61.4 ± 6.0 ml/(min·kg)] performed incremental running tests under three conditions: (1) normobaric normoxia (NN), (2) HH (2,500 m), and (3) HH with 5% CO₂ inhalation (HH+CO₂). The test under NN was always performed first, and then, the two remaining tests were completed in random and counterbalanced order. Results: End-tidal CO₂ partial pressure (55 ± 3 vs. 35 ± 1 mmHg), peak ventilation (163 ± 14 vs. 152 ± 12 l/min), and peak oxygen uptake [52.3 ± 5.5 vs. 50.5 ± 4.9 ml/(min·kg)] were all higher in the HH+CO₂ than HH trial (all p < 0.01), respectively. However, the duration of the incremental test did not differ between HH+CO₂ and HH trials. Conclusion: These data suggest that chemoreflex activation by breathing CO₂-enriched air stimulates breathing and aerobic metabolism during maximal intensity exercise without affecting exercise performance in male endurance runners under a moderately hypobaric hypoxic environment.

Sex, gender and the pulmonary physiology of exercise

In this review, we detail how the pulmonary system's response to exercise is impacted by both sex and gender in healthy humans across the lifespan. First, the rationale for why sex and gender differences should be considered is explored, and then anatomical differences are highlighted, namely that females typically have smaller lungs and airways than males. Thereafter, we describe how these anatomical differences can impact functional aspects such as respiratory muscle energetics and activation, mechanical ventilatory constraints, diaphragm fatigue, and pulmonary gas exchange in healthy adults and children. Finally, we detail how gender can impact the pulmonary response to exercise.

Biological sex can influence the pulmonary response to exercise in healthy individuals across the lifespanhttps://bit.ly/3ejMDrv

Determination of the Respiratory Compensation Point by Detecting Changes in Intercostal Muscles Oxygenation by Using Near-Infrared Spectroscopy

This study aimed to evaluate if the changes in oxygen saturation levels at intercostal muscles (SmO2-m.intercostales) assessed by near-infrared spectroscopy (NIRS) using a wearable device could determine the respiratory compensation point (RCP) during exercise. Fifteen healthy competitive triathletes (eight males; 29 ± 6 years; height 167.6 ± 25.6 cm; weight 69.2 ± 9.4 kg; V˙O2-máx 58.4 ± 8.1 mL·kg−1·min−1) were evaluated in a cycle ergometer during the maximal oxygen-uptake test (V˙O2-máx), while lung ventilation (V˙E), power output (watts, W) and SmO2-m.intercostales were measured. RCP was determined by visual method (RCPvisual: changes at ventilatory equivalents (V˙E·V˙CO2−1, V˙E·V˙O2−1) and end-tidal respiratory pressure (PetO2, PetCO2) and NIRS method (RCPNIRS: breakpoint of fall in SmO2-m.intercostales). During exercise, SmO2-m.intercostales decreased continuously showing a higher decrease when V˙E increased abruptly. A good agreement between methods used to determine RCP was found (visual vs NIRS) at %V˙O2-máx, V˙O2, V˙E, and W (Bland-Altman test). Correlations were found to each parameters analyzed (r = 0.854; r = 0.865; r = 0.981; and r = 0,968; respectively. p < 0.001 in all variables, Pearson test), with no differences (p < 0.001 in all variables, Student’s t-test) between methods used (RCPvisual and RCPNIRS). We concluded that changes at SmO2-m.intercostales measured by NIRS could adequately determine RCP in triathletes.

Time to Move Beyond a "One-Size Fits All" Approach to Inspiratory Muscle Training

Inspiratory muscle training (IMT) has been studied as a rehabilitation tool and ergogenic aid in clinical, athletic, and healthy populations. This technique aims to improve respiratory muscle strength and endurance, which has been seen to enhance respiratory pressure generation, respiratory muscle weakness, exercise capacity, and quality of life. However, the effects of IMT have been discrepant between populations, with some studies showing improvements with IMT and others not. This may be due to the use of standardized IMT protocols which are uniformly applied to all study participants without considering individual characteristics and training needs. As such, we suggest that research on IMT veer away from a standardized, one-size-fits-all intervention, and instead utilize specific IMT training protocols. In particular, a more personalized approach to an individual's training prescription based upon goals, needs, and desired outcomes of the patient or athlete. In order for the coach or practitioner to adjust and personalize a given IMT prescription for an individual, factors, such as frequency, duration, and modality will be influenced, thus inevitably affecting overall training load and adaptations for a projected outcome. Therefore, by integrating specific methods based on optimization, periodization, and personalization, further studies may overcome previous discrepancies within IMT research.

Physiological Function during Exercise and Environmental Stress in Humans-An Integrative View of Body Systems and Homeostasis

Claude Bernard's milieu intérieur (internal environment) and the associated concept of homeostasis are fundamental to the understanding of the physiological responses to exercise and environmental stress. Maintenance of cellular homeostasis is thought to happen during exercise through the precise matching of cellular energetic demand and supply, and the production and clearance of metabolic by-products. The mind-boggling number of molecular and cellular pathways and the host of tissues and organ systems involved in the processes sustaining locomotion, however, necessitate an integrative examination of the body's physiological systems. This integrative approach can be used to identify whether function and cellular homeostasis are maintained or compromised during exercise. In this review, we discuss the responses of the human brain, the lungs, the heart, and the skeletal muscles to the varying physiological demands of exercise and environmental stress. Multiple alterations in physiological function and differential homeostatic adjustments occur when people undertake strenuous exercise with and without thermal stress. These adjustments can include: hyperthermia; hyperventilation; cardiovascular strain with restrictions in brain, muscle, skin and visceral organs blood flow; greater reliance on muscle glycogen and cellular metabolism; alterations in neural activity; and, in some conditions, compromised muscle metabolism and aerobic capacity. Oxygen supply to the human brain is also blunted during intense exercise, but global cerebral metabolism and central neural drive are preserved or enhanced. In contrast to the strain seen during severe exercise and environmental stress, a steady state is maintained when humans exercise at intensities and in environmental conditions that require a small fraction of the functional capacity. The impact of exercise and environmental stress upon whole-body functions and homeostasis therefore depends on the functional needs and differs across organ systems.

Influence of High Hemoglobin-Oxygen Affinity on Humans During Hypoxia

Humans elicit a robust series of physiological responses to maintain adequate oxygen delivery during hypoxia, including a transient reduction in hemoglobin-oxygen (Hb-O₂) affinity. However, high Hb-O₂ affinity has been identified as a beneficial adaptation in several species that have been exposed to high altitude for generations. The observed differences in Hb-O₂ affinity between humans and species adapted to high altitude pose a central question: is higher or lower Hb-O₂ affinity in humans more advantageous when O₂ availability is limited? Humans with genetic mutations in hemoglobin structure resulting in high Hb-O₂ affinity have shown attenuated cardiorespiratory adjustments during hypoxia both at rest and during exercise, providing unique insight into this central question. Therefore, the purpose of this review is to examine the influence of high Hb-O₂ affinity during hypoxia through comparison of cardiovascular and respiratory adjustments elicited by humans with high Hb-O₂ affinity compared to those with normal Hb-O₂ affinity.

OUP accepted manuscript

Background

In the general population with coronavirus disease 2019 (COVID-19), obesity is associated with an increased risk of mortality. Given the typically observed obesity paradox among patients on kidney function replacement therapy (KFRT), especially dialysis patients, we examined the association of obesity with mortality among dialysis patients or living with a kidney transplant with COVID-19.

Methods

Data from the European Renal Association COVID-19 Database (ERACODA) were used. KFRT patients diagnosed with COVID-19 between 1 February 2020 and 31 January 2021 were included. The association of Quetelet's body mass index (BMI) (kg/m²), divided into: <18.5 (lean), 18.5–24.9 (normal weight), 25–29.9 (overweight), 30–34.9 (obese I) and ≥35 (obese II/III), with 3-month mortality was investigated using Cox proportional-hazards regression analyses.

Results

In 3160 patients on KFRT (mean age: 65 years, male: 61%), 99 patients were lean, 1151 normal weight (reference), 1160 overweight, 525 obese I and 225 obese II/III. During follow-up of 3 months, 28, 20, 21, 23 and 27% of patients died in these categories, respectively. In the fully adjusted model, the hazard ratios (HRs) for 3-month mortality were 1.65 [95% confidence interval (CI): 1.10, 2.47], 1 (ref.), 1.07 (95% CI: 0.89, 1.28), 1.17 (95% CI: 0.93, 1.46) and 1.71 (95% CI: 1.27, 2.30), respectively. Results were similar among dialysis patients (N = 2343) and among those living with a kidney transplant (N = 817) (P_interaction = 0.99), but differed by sex (P_interaction = 0.019). In males, the HRs for the association of aforementioned BMI categories with 3-month mortality were 2.07 (95% CI: 1.22, 3.52), 1 (ref.), 0.97 (95% CI: 0.78. 1.21), 0.99 (95% CI: 0.74, 1.33) and 1.22 (95% CI: 0.78, 1.91), respectively, and in females corresponding HRs were 1.34 (95% CI: 0.70, 2.57), 1 (ref.), 1.31 (95% CI: 0.94, 1.85), 1.54 (95% CI: 1.05, 2.26) and 2.49 (95% CI: 1.62, 3.84), respectively.

Conclusion

In KFRT patients with COVID-19, on dialysis or a kidney transplant, obesity is associated with an increased risk of mortality at 3 months. This is in contrast to the obesity paradox generally observed in dialysis patients. Additional studies are required to corroborate the sex difference in the association of obesity with mortality.

Airway luminal area and the resistive work of breathing during exercise in healthy young females and males

We examined the relationship between the work of breathing (W_b) during exercise and in vivo measures of airway size in healthy females and males. We hypothesized that sex differences in airway luminal area would explain the larger resistive W_b during exercise in females. Healthy participants (n = 11 females and n = 11 males; 19-30 yr) completed a cycle exercise test to exhaustion where W_b was assessed using an esophageal balloon catheter. On a separate day, each participant underwent a bronchoscopy procedure for optical coherence tomography measures of seven airways. In vivo measures of luminal area were made for the fourth to eighth airway generations. A composite index of airway size was calculated as the sum of the luminal area for each generation, and the total area was calculated based on Weibel's model. We found that index of airway size (males: 37.4 ± 6.3 mm² vs. females: 27.5 ± 7.4 mm²) and airway area calculated based on Weibel's model (males: 2,274 ± 557 mm² vs. females: 1,594 ± 389 mm²) were significantly larger in males (both P = 0.003). When minute ventilation was greater than ∼60 L·min^-1, the resistive W_b was higher in females. At the highest equivalent flow achieved by all subjects, resistance to inspired flow was larger in females and significantly associated with two measures of airway size in all subjects: index of airway size (r = 0.524, P = 0.012) and Weibel area (r = 0.525, P = 0.012). Our findings suggest that innate sex differences in luminal area result in a greater resistive W_b during exercise in females compared with males.NEW & NOTEWORTHY We hypothesized that the higher resistive work of breathing in females compared with males during high-intensity exercise is due to smaller airways. In vivo measures of the fourth to eighth airway generations made using optical coherence tomography show that females tend to have smaller airway luminal areas of the fourth to sixth airway generations. Sex differences in airway luminal area result in a greater resistive work of breathing during exercise in females compared with males.

Pulmonary and Inspiratory Muscle Function Response to a Mountain Ultramarathon

The study aimed to provide within-race data on the time course of pulmonary function during a mountain ultramarathon (MUM). Additionally, we wanted to assess possible sex differences regarding pre- to post-race change in pulmonary and inspiratory muscle function. Lastly, we were interested in evaluating whether changes in respiratory function were associated with relative running speed and due to general or specific fatigue. 47 athletes (29 males and 18 females; 41 ± 5 years) were submitted to a cardiopulmonary exercise test (CPET) before a 107-km MUM. Spirometric variables: forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), FEV₁/FVC and peak expiratory flow (PEF); maximal inspiratory pressure (MIP); squat jump (SJ) and handgrip strength (HG) were assessed before and after the race. Additionally PEF was measured at three aid stations (33^rd, 66^th and 84^th km) during the race. PEF declined from the 33^rd to the 66^th km (p = 0.004; d = 0.72) and from the 84^th km to the finish line (p = 0.003; d = 0.90), while relative running speed dropped from the first (0-33 km) to the second (33-66 km) race section (p < 0.001; d = 1.81) and from the third (66-84 km) to the last race section (p < 0.001; d = 1.61). Post-race, a moderate reduction was noted in FVC (-13%; p < 0.001; d = 0.52), FEV₁ (-19.5%; p < 0.001; d = 0.65), FEV₁/FVC (-8.4%; p = 0.030; d = 0.59), PEF (-20.3%; p < 0.001; d = 0.58), MIP (-25.3%; p < 0.001; d = 0.79) and SJ (-31.6%; p < 0.001; d = 1.42). Conversely, HG did not change from pre- to post-race (-1.4%; p = 0.56; d = 0.05). PEF declined during the race in parallel with running speed drop. No sex differences were noted regarding post-race respiratory function, except that FEV₁/FVC decay was significantly greater among women. The magnitude of pre- to post-race respiratory function decline was uncorrelated with relative running speed.

Predictors of outcome in patients with myasthenic crisis undergoing non-invasive mechanical ventilation: A retrospective 20 year longitudinal cohort study from a single Italian center

About 20% of patients with myasthenia gravis (MG) may develop myasthenic crisis (MC) requiring ventilation, either invasive (MV) or non-invasive (NIV) and intensive unit care (ICU). NIV failure in patients with MC can occur up to 60% of cases admitted to ICU. Moreover it is not known the outcome of MC receiving NIV. Purpose of this study was to identify predictors of outcome in MC who underwent non-invasive ventilator support outside ICU setting. We enrolled 90 patients, 53 females and 37 males admitted to University Hospital of Modena (Italy) between January 2000 and September 2020. Median age at MC was 65 years. Thirty-four patients (37.8%) required MV. Thymectomy was performed in 45 cases, associated with thymoma in 55%, with hyperplastic thymus in 33%. First-line treatment was plasmaexchange (38.8%) or intravenous immunoglobulins (45.6%). Males exhibited higher risk of MV than females .Patients in MV were treated with plasmaexchange as first-line therapy . Our in-hospital mortality rate was low. Nine patients underwent tracheostomy which was significantly related to male gender. Comorbidities had significant effect on length of ICU .Our study confirms as predictors of prognosis in our patients male gender, older age at onset, infections as trigger, pneumonia.

Effects of visual feedback of thoracoabdominal motion on oxygen consumption during hyperventilation - Pilot study

INTRODUCTION

Respiratory muscle oxygen consumption increases with the work of breathing. We hypothesized that reducing excessive respiratory muscle activity during exercise may improve exercise tolerance.

METHOD

We developed a device to provide real-time visual feedback of thoracoabdominal movement and used it to examine the influence of visual feedback of thoracoabdominal movement during diaphragmatic breathing on oxygen consumption in eight healthy men. While sitting on a wheelchair with the backrest reclined at 60°, oxygen consumption per body weight (VO₂/BW), minute ventilation (VE), tidal volume (VT), and breathing frequency (fR) were measured, breath-by-breath, using an expired-gas analyzer. The breathing pattern was analyzed by inductance plethysmography, with transducer bands over the chest and abdomen recording thoracoabdominal movements.

RESULTS

There was no significant difference in RatioTH-ABD and the ventilatory parameters between diaphragmatic breathing and diaphragmatic breathing with visual feedback. The average VO₂/BW during diaphragmatic breathing with visual feedback was 0.6 ml/kg lower than that during diaphragmatic breathing without visual feedback (p<0.05).

CONCLUSION

When visual feedback was used during diaphragmatic breathing, the RatioTH-ABD remained essentially unchanged, but VO₂/BW decreased significantly. This suggests that visual feedback of thoracoabdominal movement during diaphragmatic breathing may reduce respiratory muscle oxygen consumption.

Sex-Differences in the Oxygenation Levels of Intercostal and Vastus Lateralis Muscles During Incremental Exercise

This study aimed to examine sex differences in oxygen saturation in respiratory (SmO₂-m.intercostales) and locomotor muscles (SmO₂-m.vastus lateralis) while performing physical exercise. Twenty-five (12 women) healthy and physically active participants were evaluated during an incremental test with a cycle ergometer, while ventilatory variables [lung ventilation ( V . E), tidal volume (Vt), and respiratory rate (RR)] were acquired through the breath-by-breath method. SmO₂ was acquired using the MOXY^® devices on the m.intercostales and m.vastus lateralis. A two-way ANOVA (sex × time) indicated that women showed a greater significant decrease of SmO₂-m.intercostales, and men showed a greater significant decrease of SmO₂-m.vastus lateralis. Additionally, women reached a higher level of ΔSmO₂-m.intercostales normalized to V . E (L⋅min^-1) (p < 0.001), whereas men had a higher level of ΔSmO₂-m.vastus lateralis normalized to peak workload-to-weight (watts⋅kg^-1, PtW) (p = 0.049), as confirmed by Student's t-test. During an incremental physical exercise, women experienced a greater cost of breathing, reflected by greater deoxygenation of the respiratory muscles, whereas men had a higher peripheral load, indicated by greater deoxygenation of the locomotor muscles.

Evaluation of sex-based differences in airway size and the physiological implications

Recent evidence suggests healthy females have significantly smaller central conducting airways than males when matched for either height or lung volume during analysis. This anatomical sex-based difference could impact the integrative response to exercise. Our review critically evaluates the literature on direct and indirect techniques to measure central conducting airway size and their limitations. We present multiple sources highlighting the difference between male and female central conducting airway size in both pediatric and adult populations. Following the discussion of measurement techniques and results, we discuss the functional implications of these differences in central conducting airway size, including work of breathing, oxygen cost of breathing, and how these impacts will continue into elderly populations. We then discuss a range of topics for the future direction of airway differences and the benefits they could provide to both healthy and diseased populations. Specially, these sex-differences in central conducting airway size could result in different aerosol deposition or how lung disease manifests. Finally, we detail emerging techniques that uniquely allow for high-resolution imaging to be paired with detailed physiological measures.

Effects of Prior Voluntary Hyperventilation on the 3-min All-Out Cycling Test in Men

INTRODUCTION

The ergogenic effects of respiratory alkalosis induced by prior voluntary hyperventilation (VH) are controversial. This study examined the effects of prior VH on derived parameters from the 3-min all-out cycling test (3MT).

METHODS

Eleven men ( = 46 ± 8 mL·kg-1·min-1) performed a 3MT preceded by 15 min of rest (CONT) or VH ( = 38 ± 5 L·min-1) with PETCO2 reduced to 21 ± 1 mm Hg (HYP). End-test power (EP; synonymous with critical power) was calculated as the mean power output over the last 30 s of the 3MT, and the work done above EP (WEP; synonymous with W') was calculated as the power-time integral above EP.

RESULTS

At the start of the 3MT, capillary blood PCO2 and [H+] were lower in HYP (25.2 ± 3.0 mm Hg, 27.1 ± 2.6 nmol·L-1) than CONT (43.2 ± 2.0 mm Hg, 40.0 ± 1.5 nmol·L-1) (P < 0.001). At the end of the 3MT, blood PCO2 was still lower in HYP (35.7 ± 5.4 mm Hg) than CONT (40.6 ± 5.0 mm Hg) (P < 0.001). WEP was 10% higher in HYP (19.4 ± 7.0 kJ) than CONT (17.6 ± 6.4 kJ) (P = 0.006), whereas EP was 5% lower in HYP (246 ± 69 W) than CONT (260 ± 74 W) (P = 0.007). The ΔWEP (J·kg-1) between CONT and HYP correlated positively with the PCO2 immediately before the 3MT in HYP (r = 0.77, P = 0.006).

CONCLUSION

These findings suggest that acid-base changes elicited by prior VH increase WEP but decrease EP during the all-out 3MT.

An integrative approach to the pulmonary physiology of exercise: when does biological sex matter?

Historically, many studies investigating the pulmonary physiology of exercise (and biomedical research in general) were performed exclusively or predominantly with male research participants. This has led to an incomplete understanding of the pulmonary response to exercise. More recently, important sex-based differences with respect to the human respiratory system have been identified. The purpose of this review is to summarize current findings related to sex-based differences in the pulmonary physiology of exercise. To that end, we will discuss how morphological sex-based differences of the respiratory system affect the respiratory response to exercise. Moreover, we will discuss sex-based differences of the physiological integrative responses to exercise, and how all these differences can influence the regulation of breathing. We end with a brief discussion of pregnancy and menopause and the accompanying ventilatory changes observed during exercise.

COVID-19 and physical activity in sedentary individuals: differences in metabolic, cardiovascular, and respiratory responses during aerobic exercise performed with and without a surgical face masks

BACKGROUND

The Coronavirus-19 (COVID-19) impairs metabolic, cardiovascular, and pulmonary functions in human metabolism, and wearing face masks is recommended for the prevention of contracting or exposing others to cardio-respiratory infections. Since the effect of wearing a surgical face mask (SFM) on cardiopulmonary exercise capacity has not been systematically reported we aimed to determine the effects of wearing SFM during an incremental walking test on metabolic, cardiovascular, and pulmonary gas exchange responses in sedentary individuals.

METHODS

The evaluations were performed using a repeated measures study design. Seven sedentary males (age:40years, height:178cm, weight:88kg, BMI:28kg/m2, VO2max:32.7±3.9ml/kg/min) and 7 sedentary female participants (age:34years, height:169cm, weight:62kg, BMI:22kg/m2, VO2max:32.1±6.8 ml/kg/min) volunteered to participate in the current study. Anthropometric parameters were measured using a Bioelectrical impedance analysis prior to each testing session. The measures of lung function assessed by spirometry, breathing pattern, maximal exercise capacity with-and-without mask were measured with a breath-by-breath automated exercise metabolic system during incremental Bruce protocol on a treadmill with two consecutive sessions with 48-h intervals. Blood pressure values (systolic and diastolic pressure) of the individuals were taken and recorded within 1 minute at the end of every ten minutes, without speed changes.

RESULTS

VO2, VCO2, and VE were significantly lower during exercise performed with SFM (p<0.001). Heart rate, systolic and diastolic blood pressure were also found significantly higher during exercise performed with SFM (p<0.01).

CONCLUSIONS

Wearing a SFM during incremental walking predispose a decrease in oxygen delivery while increasing pulmonary ventilation in sedentary individuals. Thus, it could be speculated that surgical face masks have a negative impact on oxygen delivery during exercise which results in decreased exercise performance due to the restricted ventilatory conditions.

The Oxygen Cascade During Exercise in Health and Disease

The oxygen transport cascade describes the physiological steps that bring atmospheric oxygen into the body where it is delivered and consumed by metabolically active tissue. As such, the oxygen cascade is fundamental to our understanding of exercise in health and disease. Our narrative review will highlight each step of the oxygen transport cascade from inspiration of atmospheric oxygen down to mitochondrial consumption in both healthy active males and females along with clinical conditions. We will focus on how different steps interact along with principles of homeostasis, physiological redundancies, and adaptation. In particular, we highlight some of the parallels between elite athletes and clinical conditions in terms of the oxygen cascade.

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.

The effect of estimating chest wall compliance on the work of breathing during exercise as determined via the modified Campbell diagram

The modified Campbell diagram provides one of the most comprehensive assessments of the work of breathing (Wb) during exercise, wherein the resistive and elastic work of inspiration and expiration are quantified. Importantly, a necessary step in constructing the modified Campbell diagram is to obtain a value for chest wall compliance (C_CW). To date, it remains unknown whether estimating or directly measuring C_CW impacts the Wb, as determined by the modified Campbell diagram. Therefore, the purpose of this study was to evaluate whether the components of the Wb differ when the modified Campbell diagram is constructed using an estimated versus measured value of C_CW. Forty-two participants (n = 26 men, 16 women) performed graded exercise to volitional exhaustion on a cycle ergometer. C_CW was measured directly at rest via quasistatic relaxation. Estimated values of C_CW were taken from prior literature. The measured value of C_CW was greater than that obtained via estimation (214 ± 52 mL/cmH₂O vs. 189 ± 18 mL/cmH₂O; P < 0.05). At modest-to-high minute ventilations (i.e., 50-200 L/min), the inspiratory elastic Wb was greater and expiratory resistive Wb was lower, when modified Campbell diagrams were constructed using estimated compared with measured values of C_CW (P = 0.001). These differences were however small and never exceeded ±5%. Thus, although our findings demonstrate that estimating C_CW has a measurable impact on the determination of the Wb, its effect appears relatively small within a cohort of healthy adults during graded exercise.

Face Masks and the Cardiorespiratory Response to Physical Activity in Health and Disease

To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control and Prevention and the World Health Organization recommend wearing face masks in public. Some have expressed concern that these may affect the cardiopulmonary system by increasing the work of breathing, altering pulmonary gas exchange and increasing dyspnea, especially during physical activity. These concerns have been derived largely from studies evaluating devices intentionally designed to severely affect respiratory mechanics and gas exchange. We review the literature on the effects of various face masks and respirators on the respiratory system during physical activity using data from several models: cloth face coverings and surgical masks, N95 respirators, industrial respirators, and applied highly resistive or high-dead space respiratory loads. Overall, the available data suggest that although dyspnea may be increased and alter perceived effort with activity, the effects on work of breathing, blood gases, and other physiological parameters imposed by face masks during physical activity are small, often too small to be detected, even during very heavy exercise. There is no current evidence to support sex-based or age-based differences in the physiological responses to exercise while wearing a face mask. Although the available data suggest that negative effects of using cloth or surgical face masks during physical activity in healthy individuals are negligible and unlikely to impact exercise tolerance significantly, for some individuals with severe cardiopulmonary disease, any added resistance and/or minor changes in blood gases may evoke considerably more dyspnea and, thus, affect exercise capacity.

The cardiovascular consequences of fatiguing expiratory muscle work in otherwise resting healthy humans

In 11 healthy adults (25 ± 4 yr; 2 female, 9 male subjects), we investigated the effect of expiratory resistive loaded breathing [65% maximal expiratory mouth pressure (MEP), 15 breaths·min^-1, duty cycle 0.5; ERL_Pm] on mean arterial pressure (MAP), leg vascular resistance (LVR), and leg blood flow ([Formula: see text]). On a separate day, a subset of five male subjects performed ERL targeting 65% of maximal expiratory gastric pressure (ERL_Pga). ERL-induced expiratory muscle fatigue was confirmed by a 17 ± 5% reduction in MEP (P < 0.05) and a 16 ± 12% reduction in the gastric twitch pressure response to magnetic nerve stimulation (P = 0.09) from before to after ERL_Pm and ERL_Pga, respectively. From rest to task failure in ERL_Pm and ERL_Pga, MAP increased (ERL_Pm = 31 ± 10 mmHg, ERL_Pga = 18 ± 9 mmHg, both P < 0.05), but group mean LVR and [Formula: see text] were unchanged (ERL_Pm: LVR = 0.78 ± 0.21 vs. 0.97 ± 0.36 mmHg·mL^-1·min, [Formula: see text] = 133 ± 34 vs. 152 ± 74 mL·min^-1; ERL_Pga: LVR = 0.70 ± 0.21 vs. 0.84 ± 0.33 mmHg·mL^-1·min, [Formula: see text] = 160 ± 48 vs. 179 ± 110 mL·min^-1) (all P ≥ 0.05). Interestingly, [Formula: see text] during ERL_Pga oscillated within each breath, increasing (∼66%) and decreasing (∼50%) relative to resting values during resisted expirations and unresisted inspirations, respectively. In conclusion, fatiguing expiratory muscle work did not affect group mean LVR or [Formula: see text] in otherwise resting humans. We speculate that any sympathetically mediated peripheral vasoconstriction was counteracted by transient mechanical effects of high intra-abdominal pressures during ERL.NEW & NOTEWORTHY Fatiguing expiratory muscle work in otherwise resting humans elicits an increase in sympathetic motor outflow; whether limb blood flow ([Formula: see text]) and leg vascular resistance (LVR) are affected remains unknown. We found that fatiguing expiratory resistive loaded breathing (ERL) did not affect group mean [Formula: see text] or LVR. However, within-breath oscillations in [Formula: see text] may reflect a sympathetically mediated vasoconstriction that was counteracted by transient increases in [Formula: see text] due to the mechanical effects of high intra-abdominal pressure during ERL.

Do Sex Differences in Physiology Confer a Female Advantage in Ultra-Endurance Sport?

Ultra-endurance has been defined as any exercise bout that exceeds 6 h. A number of exceptional, record-breaking performances by female athletes in ultra-endurance sport have roused speculation that they might be predisposed to success in such events. Indeed, while the male-to-female performance gap in traditional endurance sport (e.g., marathon) remains at ~ 10%, the disparity in ultra-endurance competition has been reported as low as 4% despite the markedly lower number of female participants. Moreover, females generally outperform males in extreme-distance swimming. The issue is complex, however, with many sports-specific considerations and caveats. This review summarizes the sex-based differences in physiological functions and draws attention to those which likely determine success in extreme exercise endeavors. The aim is to provide a balanced discussion of the female versus male predisposition to ultra-endurance sport. Herein, we discuss sex-based differences in muscle morphology and fatigability, respiratory-neuromechanical function, substrate utilization, oxygen utilization, gastrointestinal structure and function, and hormonal control. The literature indicates that while females exhibit numerous phenotypes that would be expected to confer an advantage in ultra-endurance competition (e.g., greater fatigue resistance, greater substrate efficiency, and lower energetic demands), they also exhibit several characteristics that unequivocally impinge on performance (e.g., lower O₂-carrying capacity, increased prevalence of GI distress, and sex-hormone effects on cellular function/injury risk). Crucially, the advantageous traits may only manifest as ergogenic in the extreme endurance events which, paradoxically, are those that females less often contest. The title question should be revisited in the coming years, when/if the number of female participants increases.

Age and sex differences in blood pressure responses during hyperpnoea

NEW FINDINGS

What is the central question of this study? Increased respiratory muscle activation is associated with neural and cardiovascular consequences via the respiratory muscle-induced metaboreflex. Does ageing and/or sex influence the arterial blood pressure response during voluntary normocapnic incremental hyperpnoea? What is the main finding and its importance? The increase in blood pressure during hyperpnoea was smaller in younger females than in older females, whereas no difference was found between older males and older females. The blunted respiratory muscle-induced metaboreflex in younger females is normalized with advancing age, whereas ageing has no such effect in males.

ABSTRACT

We hypothesized that older females (OF) have a greater arterial blood pressure response to increased respiratory muscle work compared with younger females (YF) and that no such difference exists between older males (OM) and younger males (YM). To test these hypotheses, cardiovascular responses during voluntary normocapnic incremental hyperpnoea were evaluated and compared between older and younger subjects. An incremental respiratory endurance test (IRET) was performed as follows: target minute ventilation was initially set at 30% of the maximal voluntary ventilation (MVV12) and was increased by 10% of MVV12 every 3 min. The test was terminated when the subject could not maintain the target percentage of MVV12. Heart rate and mean arterial blood pressure (MAP) were recorded continuously. The increase in MAP from baseline (ΔMAP) during the IRET in OM (+24.0 ± 14.7 mmHg, mean ± SD) did not differ (P = 0.144) from that in YM (+24.3 ± 13.4 mmHg), but it was greater (P = 0.004) in OF (+31.2 ± 11.6 mmHg) than in YF (+10.3 ± 5.5 mmHg). No significant difference in ΔMAP during the IRET was observed between OM and OF (P = 0.975). These results suggest that the respiratory muscle-induced metaboreflex is blunted in YF, but it could be normalized with advancing age. In males, ageing has little effect on the respiratory muscle-induced metaboreflex. These results show no sex difference in the respiratory muscle-induced metaboreflex in older adults.

Near-infrared spectroscopy measures of sternocleidomastoid blood flow during exercise and hyperpnoea

NEW FINDINGS

What is the central question of this study? How does sternocleidomastoid blood flow change in response to increasing ventilation and whole-body exercise intensity? What is the main finding and its importance? Sternocleidomastoid blood flow increased with increasing ventilation. For a given ventilation, sternocleidomastoid blood flow was lower during whole-body exercise compared to resting hyperpnoea. These findings suggest that locomotor muscle work exerts an effect on respiratory muscle blood flow that can be observed in the sternocleidomastoid.

ABSTRACT

Respiratory muscle work influences the distribution of blood flow during exercise. Most studies have focused on blood flow to the locomotor musculature rather than the respiratory muscles, owing to the complex anatomical arrangement of respiratory muscles. The purpose of this study was to examine how accessory respiratory (i.e. sternocleidomastoid, and muscles in the intercostal space) muscle blood flow changes in response to locomotor muscle work. Seven men performed 5 min bouts of constant load cycling exercise trials at 30%, 60% and 90% of peak work rate in a randomized order, followed by 5 min bouts of voluntary hyperpnoea (VH) matching the ventilation achieved during each exercise (EX) trial. Blood-flow index (BFI) of the vastus lateralis, sternocleidomastoid (SCM) and seventh intercostal space (IC) were estimated using near-infrared spectroscopy and indocyanine green and expressed relative to resting levels. BFI_SCM was greater during VH compared to EX (P = 0.002) and increased with increasing exercise intensity (P = 0.036). BFI_SCM reached 493 ± 219% and 301 ± 215% rest during VH and EX at 90% peak work rate, respectively. BFI_IC increased to 242 ± 178% and 210 ± 117% rest at 30% peak work rate during VH and EX, respectively. No statistically significant differences in BFI_IC were observed with increased work rate during VH or EX (both P > 0.05). Moreover, there was no observed difference in BFI_IC between conditions (P > 0.05). BFI_SCM was lower for a given minute ventilation during EX compared to VH, suggesting that accessory respiratory muscle blood flow is influenced by whole-body exercise.

Physiological sex differences affect the integrative response to exercise: acute and chronic implications

NEW FINDINGS

What is the topic of this review? We review sex differences within physiological systems implicated in exercise performance; specifically, how they integrate to determine metabolic thresholds and fatigability. Thereafter, we discuss the implications that these sex differences might have for long-term adaptation to exercise. What advances does it highlight? The review collates evidence from recent physiological studies that have investigated sex as a biological variable, demonstrating that the physiological response to equivalent 'dosages' of exercise is not the same in males and females; thus, highlighting the need to research diversity in physiological responses to interventions.

ABSTRACT

The anatomical and physiological differences between males and females are thought to determine differences in the limits of human performance. The notion of studying sex as a biological variable has recently been emphasized in the biosciences as a vital step in enhancing human health. In this review, we contend that the effects of biological sex on acute and chronic responses must be studied and accounted for when prescribing aerobic exercise, much like any intervention targeting the optimization of physiological function. Emerging evidence suggests that the response of physiological systems to exercise differs between males and females, potentially mediating the beneficial effects in healthy and clinical populations. We highlight evidence that integrative metabolic thresholds during exercise are influenced by phenotypical sex differences throughout many physiological systems. Furthermore, we discuss evidence that female skeletal muscle is more resistant to fatigue elicited by equivalent dosages of high-intensity exercise. How the different acute responses affect the long-term trainability of males and females is considered, with discussion about tailoring exercise to the characteristics of the individual presented within the context of biological sex. Finally, we highlight the influence of endogenous and exogenous sex hormones on physiological responses to exercise in females. Sex is one of many mediating influences on the outcomes of exercise, and with careful experimental designs, physiologists can advance the collective understanding of diversity in physiology and optimize outcomes for both sexes.