Effects of hypoxia on exercise-induced diaphragm fatigue in healthy males and females.

Following high-intensity, normoxic exercise there is evidence to show that healthy females, on average, exhibit less fatigue of the diaphragm relative to males. In the present study, we combined hypoxia with exercise to test the hypothesis that males and females would develop a similar degree of diaphragm fatigue following cycle exercise at the same relative exercise intensity. Healthy young participants (n = 10 male; n = 10 female) with a high aerobic capacity (120% predicted) performed two time-to-exhaustion (TTE; ~85% maximum) cycle tests on separate days breathing either a normoxic or hypoxic (FiO2  = 0.15) gas mixture. Fatigue of the diaphragm was assessed in response to cervical magnetic stimulation prior to, immediately post-exercise, 10-, 30-, and 60-min post-exercise. Males and females had similar TTE durations in normoxia (males: 690 ± 181 s; females: 852 ± 401 s) and hypoxia (males: 381 ± 160 s; females: 400 ± 176 s) (p > 0.05). Cycling time was significantly shorter in hypoxia versus normoxia in both males and females (p < 0.05) and did not differ on the basis of sex (p > 0.05). Following the hypoxic TTE tests, males and females experienced a similar degree of diaphragm fatigue compared to normoxia as shown by 20%-25% reductions in transdiaphragmatic twitch pressure. This occurred despite the fact that exercise time in hypoxia was substantially shorter relative to normoxia and the cumulative diaphragm work was lower. We also observed that females did not fully recover from diaphragm fatigue in hypoxia, whereas males did (p < 0.05). Sex differences in the rate of diaphragm contractility recovery following exercise in hypoxia might relate to sex-based differences in substrate utilization or diaphragm blood flow.

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.

Effects of Aging on Hemodynamic Kinetics in Different Intensities of Dynamic Exercise.

Healthy aging hemodynamics is known to exhibit a time-dependent loss of function. We aimed at verifying whether older men would have a slowed cardiac output and stroke volume dynamics in response to the onset ("on") and on recovery ("off") of exercise in comparison to young men. Twenty healthy active men (10 young and 10 older) were recruited. Participants performed an incremental cardiopulmonary exercise testing on a cycle ergometer, and on another day, 3 constant workload tests in different intensities. Compared to younger, older men exhibited a slower cardiac output and stroke volume dynamics in both on and off transients for all exercise intensities (all P < 0.05). During higher intensities, both younger and older men had slower hemodynamic kinetics compared to lower intensities (all P < 0.05). There was strong negative relationship between the time constant of cardiac output on-kinetics during high-intensity with maximal exercise performance in both groups (r = -0.88, P < 0.01). We interpret these findings to mean that healthy older men have slowed hemodynamic kinetics compared to younger, but this difference becomes less evident in higher intensities of exercise.

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.

Exercise-Based Pulmonary Rehabilitation for Interstitial Lung Diseases: A Review of Components, Prescription, Efficacy, and Safety.

Interstitial lung diseases (ILDs) comprise a heterogeneous group of disorders (such as idiopathic pulmonary fibrosis, sarcoidosis, asbestosis, and pneumonitis) characterized by lung parenchymal impairment, inflammation, and fibrosis. The shortness of breath (i.e., dyspnea) is a hallmark and disabling symptom of ILDs. Patients with ILDs may also exhibit skeletal muscle dysfunction, oxygen desaturation, abnormal respiratory patterns, pulmonary hypertension, and decreased cardiac function, contributing to exercise intolerance and limitation of day-to-day activities. Pulmonary rehabilitation (PR) including physical exercise is an evidence-based approach to benefit functional capacity, dyspnea, and quality of life in ILD patients. However, despite recent advances and similarities with other lung diseases, the field of PR for patients with ILD requires further evidence. This mini-review aims to explore the exercise-based PR delivered around the world and evidence supporting prescription modes, considering type, intensity, and frequency components, as well as efficacy and safety of exercise training in ILDs. This review will be able to strengthen the rationale for exercise training recommendations as a core component of the PR for ILD patients.

Sex differences in diaphragmatic fatigue: Effects of hypoxia during inspiratory loading.

KEY POINTS: Under normoxic conditions, both healthy female and male diaphragms fatigue at a similar degree when matched for absolute diaphragmatic work during inspiratory loading. We investigated whether similarities in diaphragm fatigability persist under acute hypoxic conditions. We found that, in acute hypoxia, fatigue of the diaphragm is greater in women compared to men, whereas the magnitude of fatigue in normoxia did not differ between sexes. When matched for maximal diaphragm strength, women and men had a similar pressor response to work-matched inspiratory loading, independent of oxygen availability. ABSTRACT: In normoxia, women and men display a comparable magnitude of diaphragmatic fatigue (DF) after work-matched inspiratory loading. Whether these sex similarities are maintained under acute hypoxic conditions is unknown. We investigated the influence of acute hypoxia during work-matched inspiratory pressure-threshold loading (PTL) on DF in healthy women (n = 8) and men (n = 8). Two 5 min isocapnic PTL tasks targeting a transdiaphragmatic pressure (Pdi ) of 92 cmH2 O in normoxia and hypoxia (8% O2 ) were performed on separate days (≥48 h). DF was quantified by twitch Pdi (Pdi,tw ) via cervical magnetic stimulation post-PTL. Women and men had similar maximal Pdi (Pdi,max ; women: 171 ± 16, men: 178 ± 20 cmH2 O) and relative target workload (women: 54 ± 5%, men: 53 ± 6% Pdi,max ). The absolute cumulative diaphragmatic work did not differ between sexes in normoxia (women: 12,653 ± 1796 cmH2 O s-1 , men: 13,717 ± 1231 cmH2 O s-1 ; P = 0.202) or hypoxia (women: 11,624 ± 1860 cmH2 O s-1 , men: 12 722 ± 1502 cmH2 O s-1 ; P = 0.189). In normoxia, the magnitude of reduction in Pdi,tw post-PTL was similar between sexes (women: -21.1 ± 8.4%, men: -22.5 ± 4.9 %; P = 0.193); however, a higher degree of DF was observed in women compared to men following PTL in acute hypoxia (women: -27.6 ± 7.7%, men: -23.4 ± 9.6%, P = 0.019). We conclude that the female diaphragm is more susceptible to fatigue after inspiratory loading under acute hypoxic conditions. This finding may be related to sex differences in diaphragm muscle metabolism, such as fibre type composition, contractile properties, substrate utilisation and blood perfusion.

The Relationship Between Repeated-Sprint Ability, Aerobic Capacity, and Oxygen Uptake Recovery Kinetics in Female Soccer Athletes.

This study investigated the relationship between repeated-sprint ability, aerobic capacity, and oxygen uptake kinetics during the transition between exercise and recovery (off-transient) in female athletes of an intermittent sport modality. Eighteen professional soccer players completed three tests: 1) a maximal incremental exercise test; 2) a constant speed time-to-exhaustion test; and 3) a repeated-sprint ability test consisting of six 40-m sprints with 20 s of passive recovery in-between. Correlations between time-to-exhaustion, repeated-sprint ability, and oxygen uptake kinetics were calculated afterwards. The level of significance was set at p < 0.05. A performance decrement during repeated-sprint ability was found to be related to: 1) time-to-exhaustion (e.g., exercise tolerance; r = -0.773, p < 0.001); 2) oxygen uptake recovery time (r = 0.601, p = 0.008); and 3) oxygen uptake mean response time of recovery (r = 0.722, p < 0.001). Moreover, the best sprint time (r = -0.601, p = 0.008) and the mean sprint time (r = -0.608, p = 0.007) were found to be related to maximal oxygen uptake. Collectively, these results reinforce the relation between oxygen uptake kinetics and the ability to maintain sprint performance in female athletes. These results may contribute to coaches and training staff of female soccer teams to focus on training and improve their athletes' aerobic capacity and recovery capacity to improve intermittent exercise performance.

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. BFISCM was greater during VH compared to EX (P = 0.002) and increased with increasing exercise intensity (P = 0.036). BFISCM reached 493 ± 219% and 301 ± 215% rest during VH and EX at 90% peak work rate, respectively. BFIIC increased to 242 ± 178% and 210 ± 117% rest at 30% peak work rate during VH and EX, respectively. No statistically significant differences in BFIIC were observed with increased work rate during VH or EX (both P > 0.05). Moreover, there was no observed difference in BFIIC between conditions (P > 0.05). BFISCM 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.

Short-term effects of maximal dynamic exercise on flow-mediated dilation in professional female soccer players.

BACKGROUND: Endothelial function assessment may provide important insights into the cardiovascular function and long-term effects of exercise training. Many studies have investigated the possible negative effects on cardiovascular function due to extreme athletic performance, leading to undesirable effects. The purposes of this study were to investigate the acute effects of maximal intensity exercise on endothelium-dependent vasodilation, and to understand the patterns of flow-mediated dilation (FMD) change following maximal exercise in elite female athletes with a high-volume training history. METHODS: Twenty-six elite female soccer players (mean age, 22±4 years; BMI, 21±2 kg/m2; VO2max, 41±4 mL/kg/min) were evaluated. Brachial artery FMD was determined using high-resolution ultrasound at rest, and after 15 and 60 min of maximal cardiopulmonary exercise (CPX) testing on a treadmill. Flow velocity was measured at baseline and during reactive hyperemia at the same periods. RESULTS: Rest FMD was 12.4±5.5%. Peak diameter in response to reactive hyperemia was augmented after 15 min of CPX (3.5±0.4 vs. 3.6±0.4 mm, P<0.05), returning to resting values after 60 min. However, %FMD did not change among time periods. There were two characteristic patterns of FMD response following CPX. Compared to FMD at rest, half of the subjects responded with an increased FMD following maximum exercise (10.5±6.1 vs. 17.8±7.5%, P<0.05). The other subjects demonstrated a reduced FMD response following maximum exercise (14.2±4.3 vs. 10.9±3.2%, P<0.01). CONCLUSIONS: These results indicate that elite female soccer players presented robust brachial artery FMD at rest, with a heterogeneous FMD response to acute exercise with a 50% FMD improvement rate.

Effects of acute inspiratory loading during treadmill running on cerebral, locomotor and respiratory muscle oxygenation in women soccer players.

Respiratory limitation can be a primary mechanism for exercise cessation in female athletes. This study aimed to assess the effects of inspiratory loading (IL) on intercostal muscles (IM), vastus lateralis (VL) and cerebral (Cox) muscles oxygenation in women soccer players during high-intensity dynamic exercise. Ten female soccer players were randomized to perform in order two constant-load tests on a treadmill until the exhaustion time (Tlim) (100 % of maximal oxygen uptake- V˙O2). They breathed freely or against a fixed inspiratory loading (IL) of 41 cm H2O (∼30 % of maximal inspiratory pressure). Oxygenated (Δ[OxyHb]), deoxygenated (Δ[DeoxyHb]), total hemoglobin (Δ[tHb]) and tissue saturation index (ΔTSI) were obtained by NIRs. Also, blood lactate [La-] was obtained. IL significantly reduced Tlim (224 ± 54 vs 78 ± 20; P < 0.05) and increased [La-], V˙O2, respiratory cycles and dyspnea when corrected to Tlim (P < 0.05). IL also resulted in decrease of Δ[OxyHb] of Cox and IM during exercise compared with rest condition. In addition, decrease of Δ[OxyHb] was observed on IM during exercise when contrasted with Sham (P < 0.05). Furthermore, significant higher Δ[DeoxyHb] of IM and significant lower Δ[DeoxyHb] of Cox were observed when IL was applied during exercise in contrast with Sham (P < 0.05). These results were accompanied with significant reduction of Δ[tHb] and ΔTSI of IM and VL when IL was applied (P < 0.05). High-intensity exercise with IL decreased respiratory and peripheral muscle oxygenation with negative impact on exercise performance. However, the increase in ventilatory work did not impact cerebral oxygenation in soccer players.

Quantifying the mechanical work of breathing in men and women during rowing.

PURPOSE: To quantify the mechanical work of breathing (Wb) during an indoor rowing test in men and women. Additionally, to compare sex-based differences in the Wb and its components through a rowing test. METHODS: Fifteen collegiate rowers were recruited (8 women/7 men) and performed a 2000 m rowing test on a rowing ergometer. Esophageal pressure was measured during exercise via balloon catheterization, after which pressure-volume curves were used to calculate total, inspiratory resistive and elastic, and total expiratory Wb. RESULTS: Men had significantly higher values of instantaneous and cumulative total Wb at and beyond 37.5% (430.4 ± 42.5 vs. 282.1 ± 45.1 J min-1, P < 0.05) and 62.5% (1946.8 ± 150.9 vs. 1360.1 ± 197.2 J, P < 0.05) total exercise time, respectively. However, when compared at the same minute ventilation, women had higher values of total (at and above ~ 140 L min-1), inspiratory resistive (at and above ~ 120 L min-1), and inspiratory elastic (at and above ~ 135 L min-1) Wb, whereas men presented higher total expiratory Wb compared to women at any ventilation. CONCLUSION: Although female rowers present higher relative values of inspiratory resistive and elastic Wb, their male counterparts develop greater ventilatory efforts during a 2000 m rowing test, resulting in a larger total mechanical Wb. We interpret these findings to mean that the Wb reflects both anatomical (i.e., airways and lung sizes) and respiratory (i.e., minute ventilation) sex differences during rowing.

Effect of diaphragm fatigue on subsequent exercise tolerance in healthy men and women.

Women are more resistant to diaphragmatic fatigue (DF) and experience an attenuated inspiratory muscle metaboreflex relative to men. The effects of such sex-based differences on whole body exercise tolerance are yet to be examined. It was hypothesized that DF induced prior to exercise would cause less of a reduction in subsequent exercise time in women compared to men. Healthy men ( n = 9, age = 24 ± 3 yr) and women ( n = 9, age = 24 ± 3 yr) completed a maximal incremental cycle test on day 1. On day 2, subjects performed isocapnic inspiratory pressure-threshold loading (PTL) to task failure followed by a constant load submaximal time-to-exhaustion (TTE) exercise test at 85% of the predetermined peak work rate. On day 3, subjects performed the same exercise test without prior induced DF. Days 2 and 3 were randomized and counterbalanced. Magnetic stimulation of the phrenic nerve roots was used to nonvolitionally assess DF by measurement of transdiaphragmatic twitch pressure ( Pdi,tw). A similar degree of DF was produced in both sexes following PTL [ Pdi,tw (% change from baseline): M = -24.6 ± 7.8%, W = -23.1 ± 5.4%; P = 0.54)]. There was a significant reduction in TTE with prior induced DF compared with the control condition in both men (10.9 ± 3.5 min vs. 13.0 ± 3.2 min, P = 0.05) and women (10.1 ± 2.4 min vs. 12.2 ± 3.3 min, P = 0.03) that did not differ in magnitude between the sexes (M = -15.8 ± 19.5%, W = -14.5 ± 19.2%, P = 0.89). In conclusion, DF negatively and equally impairs exercise tolerance independent of sex. NEW & NOTEWORTHY Women are more resistant to diaphragmatic fatigue (DF) relative to men. The effect of DF on exercise tolerance is currently being debated. Our findings show that DF negatively and equally affects exercise tolerance in healthy men and women. Mechanisms beyond the inspiratory muscle metaboreflex (e.g., dyspnea, central fatigue, breathing pattern) may explain the absence of a sex-based difference.

Sex differences in diaphragmatic fatigue: the cardiovascular response to inspiratory resistance.

KEY POINTS: Diaphragmatic fatigue (DF) elicits a sympathetically mediated metaboreflex resulting in increased heart rate, blood pressure and limb vascular resistance. Women may be more resistant to DF compared to men, and therefore it was hypothesised that women would experience an attenuated inspiratory muscle metaboreflex during inspiratory pressure-threshold loading (PTL) performed to task failure. At the time of PTL task failure, the severity of DF was not different between sexes; however, inspiratory muscle endurance time was significantly longer in women than in men. For a given cumulative diaphragmatic force output, the severity of DF was less in women than in men. Women exhibited a blunted cardiovascular response to inspiratory resistance (i.e. metaboreflex) that may have implications for exercise tolerance. ABSTRACT: Diaphragmatic fatigue (DF) elicits reflexive increases in sympathetic vasomotor outflow (i.e. metaboreflex). There is some evidence suggesting women may be more resistant to DF compared to men, and therefore may experience an attenuated inspiratory muscle metaboreflex. To this end, we sought to examine the cardiovascular response to inspiratory resistance in healthy young men (n = 9, age = 24 ± 3 years) and women (n = 9, age = 24 ± 3 years). Subjects performed isocapnic inspiratory pressure-threshold loading (PTL, 60% maximal inspiratory mouth pressure) to task failure. Diaphragmatic fatigue was assessed by measuring transdiaphragmatic twitch pressure (Pdi,tw ) using cervical magnetic stimulation. Heart rate (HR) and mean arterial pressure (MAP) were measured beat-by-beat throughout PTL via photoplethysmography, and low-frequency systolic pressure (LFSBP ; a surrogate for sympathetic vasomotor tone) calculated from arterial waveforms using power spectrum analysis. At PTL task failure, the degree of DF was similar between sexes (∼23% reduction in Pdi,tw ; P = 0.33). However, time to task failure was significantly longer in women than in men (27 ± 11 vs. 16 ± 11 min, respectively; P = 0.02). Women exhibited less of an increase in HR (13 ± 8 vs. 19 ± 12 bpm; P = 0.02) and MAP (10 ± 8 vs. 14 ± 9 mmHg; P = 0.01), and significantly lower LFSBP (23 ± 11 vs. 34 ± 8 mmHg2 ; P = 0.04) during PTL compared to men. An attenuation of the inspiratory muscle metaboreflex may influence limb and respiratory muscle haemodynamics with implications for exercise performance.

Temporal characteristics of exercise-induced diaphragmatic fatigue.

There is evidence suggesting diaphragmatic fatigue (DF) occurs relatively early during high-intensity exercise; however, studies investigating the temporal characteristics of exercise-induced DF are limited by incongruent methodology. Eight healthy adult males (25 ± 5 yr) performed a maximal incremental exercise test on a cycle ergometer on day 1. A constant-load time-to-exhaustion (TTE) exercise test was conducted on day 2 at 60% delta between the calculated gas exchange threshold and peak work rate. Two additional constant-load exercise tests were performed at the same intensity on days 3 and 4 in a random order to either 50 or 75% TTE. DF was assessed on days 2, 3, and 4 by measuring transdiaphragmatic twitch pressure (Pdi,tw) in response to cervical magnetic stimulation. DF was present after 75 and 100% TTE (≥20% decrease in Pdi,tw). The magnitude of fatigue was 15.5 ± 5.7%, 23.6 ± 6.4%, and 35.0 ± 12.1% at 50, 75, and 100% TTE, respectively. Significant differences were found between 100 to 75 and 50% TTE (both P < 0.01), and 75 to 50% TTE ( P < 0.01). There was a significant relationship between the magnitude of fatigue and cumulative diaphragm force output ( r = 0.785; P < 0.001). Ventilation, the mechanical work of breathing (WOB), and pressure-time products were not different between trials ( P > 0.05). Our data indicate that exercise-induced DF presents a relatively late onset and is proportional to the cumulative WOB; thus the ability of the diaphragm to generate pressure progressively declines throughout exercise. NEW & NOTEWORTHY The notion that diaphragmatic fatigue (DF) occurs relatively early during exercise is equivocal. Our results indicate that DF occurs during high-intensity endurance exercise in healthy men and its magnitude is strongly related to the amount of pressure and work generated by respiratory muscles. Thus we conclude that the work of breathing is the major determinant of exercise-induced DF.

Effects of inspiratory muscle training in professional women football players: a randomized sham-controlled trial.

This study was conducted to determine the effects of inspiratory muscle training (IMT) on respiratory and peripheral muscles oxygenation during a maximal exercise tolerance test and on repeated-sprint ability (RSA) performance in professional women football players. Eighteen athletes were randomly assigned to one of the following groups: SHAM (n = 8) or IMT (n = 10). After a maximal incremental exercise test, all participants performed (on a different day) a time-to-exhaustion (Tlim) test. Peripheral and respiratory muscles oxygenation by near-infrared spectroscopy, breath-by-breath ventilatory and metabolic variables, and blood lactate concentration were measured. The RSA test was performed on a grass field. After a 6 week intervention, all athletes were reevaluated. Both groups showed increases in inspiratory muscles strength, exercise tolerance and RSA performance, however only the IMT group presented lower deoxyhemoglobin and total hemoglobin blood concentrations on intercostal muscles concomitantly to an increased oxyhemoglobin and total hemoglobin blood concentrations on vastus lateralis muscle during Tlim. In conclusion, these results may indicate the potential role of IMT to attenuate inspiratory muscles metaboreflex and consequently improve oxygen and blood supply to limb muscles during high-intensity exercise, with a potential impact on inspiratory muscle strength, exercise tolerance and sprints performance in professional women football players.

Effects of respiratory muscle work on respiratory and locomotor blood flow during exercise.

NEW FINDINGS: What is the central question of this study? Does manipulation of the work of breathing during high-intensity exercise alter respiratory and locomotor muscle blood flow? What is the main finding and its importance? We found that when the work of breathing was reduced during exercise, respiratory muscle blood flow decreased, while locomotor muscle blood flow increased. Conversely, when the work of breathing was increased, respiratory muscle blood flow increased, while locomotor muscle blood flow decreased. Our findings support the theory of a competitive relationship between locomotor and respiratory muscles during intense exercise. Manipulation of the work of breathing (WOB) during near-maximal exercise influences leg blood flow, but the effects on respiratory muscle blood flow are equivocal. We sought to assess leg and respiratory muscle blood flow simultaneously during intense exercise while manipulating WOB. Our hypotheses were as follows: (i) increasing the WOB would increase respiratory muscle blood flow and decrease leg blood flow; and (ii) decreasing the WOB would decrease respiratory muscle blood flow and increase leg blood flow. Eight healthy subjects (n = 5 men, n = 3 women) performed a maximal cycle test (day 1) and a series of constant-load exercise trials at 90% of peak work rate (day 2). On day 2, WOB was assessed with oesophageal balloon catheters and was increased (via resistors), decreased (via proportional assist ventilation) or unchanged (control) during the trials. Blood flow was assessed using near-infrared spectroscopy optodes placed over quadriceps and the sternocleidomastoid muscles, coupled with a venous Indocyanine Green dye injection. Changes in WOB were significantly and positively related to changes in respiratory muscle blood flow (r = 0.73), whereby increasing the WOB increased blood flow. Conversely, changes in WOB were significantly and inversely related to changes in locomotor blood flow (r = 0.57), whereby decreasing the WOB increased locomotor blood flow. Oxygen uptake was not different during the control and resistor trials (3.8 ± 0.9 versus 3.7 ± 0.8 l min-1 , P > 0.05), but was lower on the proportional assist ventilator trial (3.4 ± 0.7 l min-1 , P < 0.05) compared with control. Our findings support the concept that respiratory muscle work significantly influences the distribution of blood flow to both respiratory and locomotor muscles.

Classical experiments in whole-body metabolism: closed-circuit respirometry.

As part of a series of reviews aimed at providing historical context to the study of whole-body metabolism, this article focuses on the technique of closed-circuit respirometry. Developed by nineteenth century physiologists Henri-Victor Regnault and Jules de Reiset, a constant-pressure closed-circuit calorimeter capable of measuring oxygen consumption and carbon dioxide production in small animals became the framework for future experiments on whole-body metabolism in humans. The volume-loss and volume-replenishment techniques can be used to indirectly assess energy expenditure using an oxygen reservoir; spirometers are simplistic in design but difficult to operate. Leaks, calibration errors, equilibration of gases and dead space are some of the major limitations of the methodology. Despite operational difficulties, closed-circuit respirometry is highly accurate and reproducible. Due to the bespoke nature of many closed-circuit systems, maintenance and repair is often troublesome. Compounded by technological advancement, closed-circuit techniques have become progressively outdated. Nevertheless, the classical experiments in whole-body metabolism played a pivotal role in furthering our understanding of basic human physiology and paved the way for current methodologies used in the field.

Reliability of the diaphragmatic compound muscle action potential evoked by cervical magnetic stimulation and recorded via chest wall surface EMG.

INTRODUCTION: Stimulation of the phrenic nerve via cervical magnetic stimulation (CMS) elicits a compound muscle action potential (CMAP) that allows for assessment of diaphragm activation. The reliability of CMS to evoke the CMAP recorded by chest wall surface EMG has yet to be comprehensively examined. METHODS: CMS was performed on healthy young males (n=10) and females (n=10). Surface EMG electrodes were placed on the right and left hemi-diaphragm between the 6-8th intercostal spaces. CMAPs were analysed for: latency, duration, peak-to-peak amplitude, and area. Reliability within and between experimental sessions was assessed using intraclass correlation coefficients (ICC). Bilateral (right-left) and sex-based (male-female) comparisons were also made (independent samples t-test). RESULTS: All CMAP characteristics demonstrated high reproducibility within (ICCs>0.96) and between (ICCs>0.89) experimental sessions. No statistically significant bilateral or sex-based differences were found (p>0.05). DISCUSSION: CMS is a reliable and non-invasive method to evaluate phrenic nerve conduction.

Deep breathing heart rate variability is associated with inspiratory muscle weakness in chronic heart failure.

BACKGROUND AND PURPOSE: There is a synchronism between the respiratory and cardiac cycles. However, the relationship of inspiratory muscle weakness in chronic heart failure (CHF) on cardiac autonomic modulation is unknown. The purpose of the present investigation was to evaluate the impact of inspiratory muscle strength on the magnitude of respiratory sinus arrhythmia. METHODS: Ten CHF (62 ± 7 years--left ventricle eject fraction of 40 ± 5% and New York Heart Association class I-III) and nine matched-age healthy volunteers (64 ± 5 years) participated in this study. Heart rate variability (HRV) was obtained at rest and during deep breathing manoeuvre (DB-M) by electrocardiograph. RESULTS: CHF patients demonstrated impaired cardiac autonomic modulation at rest and during DB-M when compared with healthy subjects (p < 0.05). Moreover, significant and positive correlations between maximal inspiratory pressure and inspiratory-expiratory differences (r = 0.79), expiratory/inspiratory ratio (r = 0.83), root mean square of the successive differences (r = 0.77), standard deviation of NN intervals (r = 0.77), low frequency (r = 0.77), and high frequency (r = 0.70) were found during DB-M. At rest, significant correlations were found also. CONCLUSION: Patients with CHF presented impaired cardiac autonomic modulation at rest. In addition, cardiac autonomic control of heart rate was associated with inspiratory muscle weakness in CHF. Based on this evidence, recommendations for future research applications of respiratory muscle training can bring to light a potentially valuable target for rehabilitation.