Influence of diaphragm and rib cage muscle fatigue on breathing during endurance exercise

Inspiratory muscle fatigue (IMF) can develop during exhaustive exercise and cause tachypnea or rapid shallow breathing. We assessed the effects of rib cage muscle (RCM-F) and diaphragm fatigue (DIA-F) on breathing pattern and respiratory mechanics during high-intensity endurance exercise. Twelve healthy subjects performed a constant-load (85% maximal power) cycling test to exhaustion with prior IMF and a cycling test of similar intensity and duration without prior IMF (control). IMF was induced by resistive breathing and assessed by oesophageal and gastric twitch pressure measurements during cervical magnetic stimulation. Both RCM-F and DIA-F increased RCM and abdominal muscle force production during exercise compared to control. With RCM-F, tidal volume decreased while it increased with DIA-F. RCM-F was associated with a smaller increase in end-expiratory oesophageal pressure (i.e. decrease in lung volume) than DIA-F. These results suggest that RCM-F and not DIA-F is associated with rapid shallow breathing and that lowering the operating lung volume with DIA-F may help to preserve diaphragmatic function.     

Impaired exercise ventilatory mechanics with the self-contained breathing apparatus are improved with heliox

The effect of the self-contained breathing apparatus (SCBA) with compressed air (BA-A) on ventilatory mechanics, work of breathing (WOB), pulmonary function, and respiratory muscle fatigue, was compared with that of a low resistance breathing valve (LRV). Further, the effect of unloading the respiratory muscles with heliox with the SCBA (BA-H) was compared with BA-A and LRV. Twelve men completed three randomized exercise trials on separate days, each consisting of three 10 min bouts of stepping exercise (Bouts 1, 2, and 3) separated by a 5 min recovery. Subjects wore firefighter protective equipment including the SCBA. At rest, FEV₁ and peak expiratory flow rates were lower with BA-A than with LRV, but were higher with BA-H than either with BA-A or LRV. After Bout 3, expiratory reserve volume, expiratory resistive WOB, and inspiratory elastic WOB were increased in BA-A compared to LRV but these were lower with BA-H compared to BA-A. After Bout 3, maximal inspiratory and expiratory pressures were reduced with BA-A, but not with LRV or BA-H. In summary, we found that the SCBA reduced resting pulmonary function, and increased expiratory reserve volume, work of breathing, and respiratory muscle fatigue during stepping exercise, and these changes can be reduced with the use of heliox.     

Task failure from inspiratory resistive loaded breathing: a role for inspiratory muscle fatigue?

The use of non-invasive resistive breathing to task failure to assess inspiratory muscle performance remains a matter of debate. CO₂ retention rather than diaphragmatic fatigue was suggested to limit endurance during inspiratory resistive breathing. Cervical magnetic stimulation (CMS) allows discrimination between diaphragmatic and rib cage muscle fatigue. We tested a new protocol with respect to the extent and the partitioning of inspiratory muscle fatigue at task failure. Nine healthy subjects performed two runs of inspiratory resistive breathing at 67 (12)% of their maximal inspiratory mouth pressure, respiratory rate ( f_R), paced at 18 min^–1, with a 15-min pause between runs. Diaphragm and rib cage muscle contractility were assessed from CMS-induced esophageal (P_es,tw), gastric (P_ga,tw), and transdiaphragmatic (P_di,tw) twitch pressures. Average endurance times of the first and second runs were similar [9.1 (6.7) and 8.4 (3.5) min]. P_di,tw significantly decreased from 33.1 to 25.9 cmH₂O in the first run, partially recovered (27.6 cmH₂O), and decreased further in the second run (23.4 cmH₂O). P_es,tw also decreased significantly (–5.1 and –2.4 cmH₂O), while P_ga,tw did not change significantly (–2.0 and –1.9 cmH₂O), indicating more pronounced rib cage rather than diaphragmatic fatigue. End-tidal partial pressure of CO₂ (P_ETCO₂) rose from 37.2 to 44.0 and 45.3 mmHg, and arterial oxygen saturation (S_aO₂) decreased in both runs from 98% to 94%. Thus, task failure in mouth-pressure-targeted, inspiratory resistive breathing is associated with both diaphragmatic and rib cage muscle fatigue. Similar endurance times despite different degrees of muscle fatigue at the start of the runs indicate that other factors, e.g. increases in P_ETCO₂, and/or decreases in S_aO₂, probably contributed to task-failure.     

Influence of anthropometric characteristics on changes in maximal exercise ventilation and breathing pattern during growth in boys

Summary The aim of this study was to investigate the effect of growth on ventilation and breathing pattern during maximal exercise oxygen consumption (VO_2max and their relationships with anthropometric characteristics. Seventy six untrained schoolboys, aged 10.5–15.5 years, participated in this study. Anthropometric measurements made included body mass, height, armspan, lean body mass, and body surface area. During an incremental exercise test, maximal ventilation (V_Emax), tidal volume (V _Tmax), breathing frequency (f _max), inspiratory and expiratory times (t _Imax and t _Emax), total duration of respiratory cycle (t _TOTmax), mean inspiratory flow (V _T/t _Imax), and inspiration fraction (t _I/t _TOTmax) were measured at VO_2max. A power function was calculated between anthropometric characteristics and ventilatory variables to determine the allometric constants. The results showed firstly, that V_Emax, V _Tmax, t _Imax, t _Emax, t _TOTmax, and V _T/t _Imax increased with age and anthropometric characteristics (P<0.001), f _max decreased (P<0.001), and t _I/t _TOTmax remained constant during growth; secondly that lean body mass explained the greatest percentage of variance of V_Emax (62.1%), V _Tmax (76.8%), and V _T/t _Imax (70.6%), while anthropometric characteristics explained a slight percentage of variance of f _max and timing; and thirdly that V_Emax, V _Tmax, and V _T/t _Imax normalized by lean body mass did not change significantly with age. We concluded that at VO_2max there were marked changes in ventilation and breathing pattern with growth. The changes in V_Emax, V _Tmax, and V _T/t _Imax were strongly related to the changes in lean body mass.     

Hypocapnia during hypoxic exercise and its impact on cerebral oxygenation,ventilation and maximal whole body O2 uptake

With hypoxic exposure ventilation is elevated through the hypoxic ventilatory response. We tested the hypothesis that the resulting hypocapnia reduces maximal exercise capacity by decreasing (i) cerebral blood flow and oxygenation and (ii) the ventilatory drive.     

Contribution of central and reflex nervous activity to the rapid increase in pulmonary ventilation at the start of muscular exercise in man

Summary To investigate the relative contributions of the central and peripheral neural drive to hyperventilation at the onset of muscular exercise, five volunteers were tested during the first ten breaths while performing both voluntary (VM) and passive (PM) ankle rotations with a frequency of 1 Hz and through an angle of 10°. Resulting breathing patterns for the two movements were compared. Hypocapnic hyperventilation, found in both PM and VM, indicated its neural origin. Respiratory changes were higher in VM than in PM. In both experimental conditions, increases in ventilation ( ) depended more on respiratory frequency (f) than on tidal volume (V _T). Moreover, increases inV _T adapted, breath-by-breath, to values lower than the initial ones, while increases inf rose progressively. Expiratory time was reduced more than inspiratory time (T _I); increases in inspiratory flow (V _T/T _I) depended to the same extent on changes in bothT _I andV _T. Increases in expiratory tidal volume were initially higher than in inspiratory tidal volume, thereby producing a reduction in functional residual capacity. Because PM respiratory changes could be considered to be of nervous reflex origin only, the identical breathing patterns in PM and VM indicated that the hyperventilation found also in VM was mainly of reflex origin. The increase in was considered to be dependent on a greater stimulus from muscle proprioreceptors.     

Influence of heat stress and acclimation on maximal aerobic power

Summary Thirteen male volunteers performed cycle ergometer maximal oxygen uptake ( tests) in moderate (21 C, 30% rh) and hot (49 C, 20% rh) environments, before and after a 9-day heat acclimation program. This program resulted in significantly decreased (P<0.01) final heart rate (24 bt·min^–1) and rectal temperature (0.4 C) from the first to last day of acclimation. The was lower (P<0.01) in the hot environment relative to the moderate environment both before (8%) and after (7%) acclimation with no significant difference (P>0.05) shown for maximal power output (PO max, watts) between environments either before or after acclimation. The was higher (P<0.01) by 4% after acclimation in both environments. Also, PO max was higher (P<0.05) after acclimation in both the moderate (4%) and hot (2%) environments. The reduction in in the hot compared to moderate environment was not related to the difference in core temperature at between moderate and hot trials, nor was it strongly related with aerobic fitness level. These findings indicate that heat stress, per se, reduced the . Further, the reduction in due to heat was not affect be state of heat acclimation, the degree of elevation in core temperature, or level of aerobic fitness.     

Effect of arm cranking exercise on skin blood flow of lower limb in people with injuries to the spinal cord

The purpose of this study was to examine whether arm cranking exercise induces changes in skin blood flow in the paralyzed lower limbs of people with injuries to the spinal cord (PISC). Ten PISC with lesions located between Th5 and L5 and six control subjects performed arm cranking exercise for 6 min at three intensities, 10, 30 and 50 W, at a room temperature of 25°C. Oxygen uptake (Vo₂) and heart rate (HR) were measured for the last 2 min of each exercise period. The skin blood flow at the anterior thigh (BF_sk,t) was continuously monitored using laser Doppler flowmetry for the whole 6-min period and for the first 10 min of recovery following exercise. During exercise, the PISC showed lower Vo₂ and greater HR than the control subjects. No increase in BF_sk,t was found in six of the PISC with lesions at or above Th12, irrespective of the exercise intensity. On the other hand, in PISC with lesions at L1 or below, BF_sk,t increased significantly (P < 0.05) with an increase in Vo₂ and HR, although the BF_sk,t at a given Vo₂ and HR was lower than that in the control subjects. These results would suggest that arm exercise can promote the blood circulation in the skin of the lower limbs if the injury level is below L1.     

Effect of exercise on metabolism of glycogen and triglycerides in the respiratory muscles

It was shown that during muscular exertion the diaphragm muscle and the intercostal muscles utilize endogenous glycogen whereas only the diaphragm muscle utilizes endogenous triglycerides. The post-excercise glycogen repletion in the diaphragm muscle was much faster than in the intercostal muscles. In the diaphragm muscle, marked overshoot of the glycogen level occurred early after the exercise.The work was supported by Polish Academy of Sciences within the project 10.4.2.01.3.2.     

Effect of hyperoxia on performance capacity of firemen

Summary We examined the effect of O₂-enriched air upon performance capacity and some physiological and psychological variables. Eight firemen were studied during seven bouts of 2 min treadmill-running while breathing air with 21 or 40% oxygen. The duration of the resting periods between the working bouts was chosed by the subjects themselves, with the instructions to rest as short as possible. Total resting time decreased by 29% and total amount of air used by 6%, under the 40% oxygen condition. There were no differences in 1) minute ventilation during working periods (when the subjects breathed 40% oxygen respiratory rate decreased whereas tidalvolume increased), 2) heart rate reached during working periods, 3) subjective feelings of fatigue as indicated by the subjects at the end of every working period.Advantages of the use of O₂-enriched air by firemen are discussed and it is concluded that breathing air with 40% oxygen does not mean an extra physiological or psychological load for the organism. Finally, possible factors that made a subject decide to start again are discussed and the importance of the respiratory rate in this decision is indicated.Students of the department of Physical Education, Free University, Amsterdam, The NetherlandsFire-brigade officer of the Amsterdam' fire-brigade, in charge of breathing protection/diving     

The effect of O2 breathing on maximal aerobic power

Summary Time of performance, blood lactic acid concentration (L.A.), heart rate (H.R.) and maximal oxygen consumption ( ) were measured during air and oxygen breathin in 11 subjects performing a supramaximal exercise with an O₂ requirement of 70 to 80 ml/kg·min to exhaustion. In addition the subjects were tested for maximal aerobic power with an indirect method. In one subject the rate of lactic acid increase in blood was also measured.The measured with both the direct and the indirect method appears to be about 8% higher when breathing pure oxygen; lactic acid production rate decreases correspondingly. Maximal H.R. and maximal L.A. concentration were found to be the same.In submaximal exercise steady state H.R. is lower by about 8–9 beats/min when breathing oxygen. Also when breathing oxygen H.R. is a linear function of the work load.From experimental data obtained in subjects of different , breathing both air or O₂, the energy equivalent of L.A. could be calculated as amounting to about 47 ml of O₂ or 235 cal per g of L.A. produced.This work was supported by a grant from the National Research Council of Italy (C.N.R.)     

Effects of spontaneously chosen crank rate variations on electromyographic responses in sub-maximal arm exercise in inexperienced subjects

The aim of the present study was to compare electromyographic responses during arm exercises with a crank rate chosen spontaneously (T_S) or set at 20% below or above (T_–20, T₊₂₀) the spontaneously chosen crank rate (SCCR). Ten male physical education students performed arm exercises with intensities ranging from 20% to 80% of maximal power. Muscular activity levels were analysed for the biceps brachii and the triceps brachii muscles using integrated rectified surface electromyography (iEMG). All values were presented as the mean and standard deviation. During T_S, the sum of iEMG for the two muscles studied was significantly (P<0.05) lower than during T₊₂₀ for each power output. No significant differences were observed in iEMG values between T_S and T_–20. The hypothesis that SCCR relates to a minimisation of muscle activation during an upper body exercise was not confirmed. Variations superior or inferior to a 20% increase of the iEMG responses do not influence it. Moreover, the selection of crank rates depends on the power output and the SCCR increased significantly (P<0.05) with increasing power output.     

Effects of loading on upper airway and respiratory pump muscle motoneurons

The functional outcomes of respiratory muscle loading by chemical (e.g. hypercapnia), mechanical (i.e. external mechanical loading) or ventilatory (e.g. exercise) factors can be either positive, such as through an increase in pressure-generating capacity of the inspiratory muscles or detrimental, such as by fatigue. Neurophysiological responses to respiratory muscle loading can occur at one or more points along the pathway from motor cortex to muscle. This paper describes the respiratory pump and upper airway motoneuron responses to the imposition of acute loads including processes of pre-activation, respiratory reflexes, potentiation and fatigue. It also considers changes suggestive of adaptation to chronic loading either from specific respiratory muscle training programs or as part of disease processes such as chronic obstructive pulmonary disease or obstructive sleep apnoea.     

Effects of unsupported arm training on arm exercise-related perception in COPD patients

We hypothesized that arm training might affect unsupported arm exercise-related perception by decreasing motor output to arm/torso muscles in patients with chronic obstructive pulmonary disease (COPD). Eleven patients were studied at 80% of peak incremental arm exercise, before and after unsupported arm training. Training increased endurance time, decreased respiratory effort and much more arm effort (by Borg scale) without affecting chest wall dynamic hyperinflation or configuration. Ventilatory response to carbon dioxide output was the same before and after training so that at isotime the reduction in ventilation correlated strongly with a simultaneous reduction in metabolic output. These changes reflect a reduced ventilatory drive. We conclude that: (i) a reduced level of ventilation, relative to a decrease in central motor output, is the contribution of arm training to symptom alleviation during unsupported arm exercise in COPD patients, and (ii) arm training improved patients’ exercise-related perception without affecting chest wall operational volumes or configuration.     

Effects of a multi-nutrient supplement on exercise performance and hormonal responses to resistance exercise

The purpose of this study was to determine the influence of a comprehensive multi-component nutritional supplement on performance, hormonal, and metabolic responses to an acute bout of resistance exercise. Nine healthy subjects ingested either Muscle Fuel™ (MF) or a matched placebo (PL) for 7 days. Subjects then reported to the laboratory, ingested the corresponding supplement, and performed two consecutive days of heavy resistance exercise testing with associated blood draws. MF supplementation improved vertical jump (VJ) power output and the number of repetitions performed at 80% of one repetition maximum (1RM). Additionally, MF supplementation potentiated growth hormone (GH), testosterone, and insulin-like growth factor-1 responses to exercise. Concentrations of circulating myoglobin and creatine kinase (CK) were attenuated immediately following resistance exercise during the MF trial, indicating that MF partially mediated some form of exercise-induced muscle tissue damage. In summary MF enhanced performance and hormonal responses associated with an acute bout of resistance exercise. These responses indicate that MF supplementation augments the quality of an acute bout of resistance exercise thereby increasing the endocrine signaling and recovery following heavy resistance exercise.     

Influence of L-carnitine administration on maximal physical exercise

Summary The effects of L-carnitine administration on maximal exercise capacity were studied in a double-blind, cross-over trial on ten moderately trained young men. A quantity of 2 g of L-carnitine or a placebo were administered orally in random order to these subjects 1 h before they began exercise on a cycle ergometer. Exercise intensity was increased by 50-W increments every 3 min until they became exhausted. After 72-h recovery, the same exercise regime was repeated but this time the subjects, who had previously received L-carnitine, were now given the placebo and vice versa. The results showed that at the maximal exercise intensity, treatment with L-carnitine significantly increased both maximal oxygen uptake, and power output. Moreover, at similar exercise intensities in the L-carnitine trial oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. It is concluded that under these experimental conditions pretreatment with L-carnitine favoured aerobic processes resulting in a more efficient performance. Possible mechanisms producing this effect are discussed.     

The effect of acute magnesium loading on the maximal exercise performance of stable chronic obstructive pulmonary disease patients

OBJECTIVE:

The potential influence of magnesium on exercise performance is a subject of increasing interest. Magnesium has been shown to have bronchodilatatory properties in asthma and chronic obstructive pulmonary disease patients. The aim of this study was to investigate the effects of acute magnesium IV loading on the aerobic exercise performance of stable chronic obstructive pulmonary disease patients.

METHODS:

Twenty male chronic obstructive pulmonary disease patients (66.2±8.3 years old, FEV₁: 49.3±19.8%) received an IV infusion of 2 g of either magnesium sulfate or saline on two randomly assigned occasions approximately two days apart. Spirometry was performed both before and 45 minutes after the infusions. A symptom-limited incremental maximal cardiopulmonary test was performed on a cycle ergometer at approximately 100 minutes after the end of the infusion. ClinicalTrials.gov: {"type":"clinical-trial","attrs":{"text":"NCT00500864","term_id":"NCT00500864"}}NCT00500864

RESULTS:

Magnesium infusion was associated with significant reductions in the functional residual capacity (-0.41 l) and residual volume (-0.47 l), the mean arterial blood pressure (-5.6 mmHg) and the cardiac double product (-734.8 mmHg.bpm) at rest. Magnesium treatment led to significant increases in the maximal load reached (+8 w) and the respiratory exchange ratio (0.06) at peak exercise. The subgroup of patients who showed increases in the work load equal to or greater than 5 w also exhibited significantly greater improvements in inspiratory capacity (0.29 l).

CONCLUSIONS:

The acute IV loading of magnesium promotes a reduction in static lung hyperinflation and improves the exercise performance in stable chronic obstructive pulmonary disease patients. Improvements in respiratory mechanics appear to be responsible for the latter finding.     

Skeletal muscle fiber type composition and performance during repeated bouts of maximal,concentric contractions

Summary Force output and fatigue and recovery patterns were studied during intermittent short-term exercise. 27 men performed three bouts of 30 maximal unilateral knee extensions on 2 different occasions. Blood flow was maintained or occluded during recovery periods (60 s). Blood flow was restricted by inflating a pneumatic cuff placed around the proximal thigh. Muscle biopsies from vastus lateralis were analyzed for identification of fast twitch (FT) and slow twitch (ST) fibers and relative FT area. Peak torque decreased during each bout of exercise and more when blood flow was restricted during recovery. Initial peak torque (IPT) and average peak torque (APT) decreased over the three exercise bouts. This response was 3fold greater without than with blood flow during recovery. IPT and APT decreased more in individuals with mainly FT fibers than in those with mainly ST fibers. It is suggested that performance during repeated bouts of maximal concentric contractions differs between individuals with different fiber type composition. Specifically, in high intensity, intermittent exercise with emphasis on anaerobic energy release a high FT composition may not necessarily be advantageous for performance.     

Influence of acute maximal exercise on lecithin: cholesterol acyltransferase activity in healthy adults of differing aerobic performance

Summary To document the possible influence of a single episode of maximal aerobic stress on the serum lecithin: cholesterol acyltransferase (LCAT) activity in subjects with differing histories of training, two groups of healthy male adults [controls (C),n = 18, 28.6 years, SD 5.2, 50.1 ml · kg^–1 · min^–1 maximal O₂ uptake (VO_2max), SD 5.3; endurance trained athletes (T),n = 18, 31.4 years, SD 8.8, 65.0 ml · kg^–1 · min^–1 VO_2max, SD 2.8] were examined in a maximal aerobic stress test. In addition to the routine assessment of lipid status, LCAT activity was measured immediately before and after exercise. At rest nearly identical LCAT activity values were found in both groups: C 64.4 nmol · ml^–1 · h^–1, SD 16.7 vs T 65.0 nmol · ml^–1 · h^–1, SD 20.9. The post-exercise LCAT values induced by the maximal stress test increased significantly to (C) 95.7 nmol · ml^–1 · h^–1, SD 23.5, +48.6%,P<0.001; (T) 83.5 nmol · ml^–1 · h^–1, SD 24.3, +29.1%,P<0.01. Neither the pre nor the post-exercise individual LCAT activity values showed any significant correlation to the corresponding data on physical performance.