Respiratory muscle endurance training reduces chronic neck pain: A pilot study.

BACKGROUND: Patients with chronic neck pain show also respiratory dysfunctions. OBJECTIVE: To investigate the effects of respiratory muscle endurance training (RMET) on chronic neck pain. METHODS: In this pilot study (single-subject design: 3 baseline measurements, 4 measurements during RMET), 15 neck patients (49.3 ± 13.7 years; 13 females) conducted 20 sessions of home-based RMET using a SpiroTiger® (normocapnic hyperpnoea). Maximal voluntary ventilation (MVV), maximal inspiratory (Pimax) and expiratory (Pemax) pressure were measured before and after RMET. Neck flexor endurance, cervical and thoracic mobility, forward head posture, chest wall expansion and self-assessed neck disability [Neck Disability Index (NDI), Bournemouth questionnaire] were weekly assessed. Repeated measure ANOVA (Bonferroni correction) compared the first and last baseline and the last measurement after RMET. RESULTS: RMET significantly increased MVV (p= 0.025), Pimax (p= 0.001) and Pemax (p< 0.001). During RMET, neck disability significantly decreased (NDI: p= 0.001; Bournemouth questionnaire: p= 0.002), while neck flexor endurance (p< 0.001) and chest wall expansion (p< 0.001) increased. The changes in respiratory and musculoskeletal parameters did not correlate. CONCLUSIONS: RMET emerged from this pilot study as a feasible and effective therapy for reducing disability in patients with chronic neck pain. The underlying mechanisms, including blood gas analyses, need further investigation in a randomized controlled study.

Respiratory dysfunction in patients with chronic neck pain - influence of thoracic spine and chest mobility.

Patients with chronic neck pain exhibit various musculoskeletal deficits and respiratory dysfunction. As there is a link between thoracic and cervical spine motion, the aim of this study was to investigate the relationship between thoracic spine and chest mobility with respiratory function and neck disability. Nineteen patients with chronic neck pain (7 male, 46.6 ± 10.5 years) and 19 healthy subjects (7 male, 46.5 ± 9.9 years) participated. Spirometry was conducted to determine maximal voluntary ventilation (MVV), maximal inspiratory (Pimax) and maximal expiratory pressure (Pemax). Thoracic spine mobility was measured using the Spinal Mouse(®). Chest expansion was assessed by subtracting chest circumference during maximal inspiration and expiration. Neck function was investigated by examining range of motion, forward head posture, neck flexor muscle synergy endurance and self-assessment (Neck disability index (NDI)). Correlation analyses and multiple linear regression analyses were conducted using MVV, Pimax and Pemax as independent variables. Thoracic spine mobility during flexion and chest expansion correlated significantly to MVV (r = 0.45 and 0.42), all neck motions (r between 0.39 and 0.59) and neck muscle endurance (rS = 0.36). Pemax and Pimax were related to NDI (r = -0.58 and -0.46). In the regression models, chest expansion was the only significant predictor for MVV, and Pemax was determined by neck muscle endurance. These results suggest that chronic neck pain patients should improve the endurance of the neck flexor muscles and thoracic spine and chest mobility. Additionally, these patients might benefit from respiratory muscle endurance training, possibly by increasing chest mobility and Pemax.

Combined effects of whole-body vibration, resistance exercise, and vascular occlusion on skeletal muscle and performance.

The purpose of this study was to evaluate the effects of a new high-intensity training modality comprised of vibration exercise with superimposed resistance exercise and vascular occlusion (vibroX) on skeletal muscle and performance. Young untrained women were randomized to either train in a progressive mode on 3 days per week for 5 weeks ( N=12) or to maintain a sedentary lifestyle ( N=9). VibroX increased peak cycling power (+9%, P=0.001), endurance capacity (+57%, P=0.002), ventilatory threshold (+12%, P<0.001), and end-test torque (+15%, P=0.002) relative to the sedentary group. Training load increased by 84.5% ( P<0.001) after vibroX. The increases were paralleled by increases in myosin heavy chain type 1 vastus lateralis muscle fiber cross-sectional area (+14%, P=0.031) and proportion (+17%, P=0.015), thigh lean mass (+4%, P=0.001), capillary-to-fiber ratio (+14%, P=0.003), and cytochrome c oxidase activity. Conversely, maximal values for oxygen consumption, cardiac output, isokinetic leg extension power and jumping power remained unaffected. Notably, vastus lateralis muscle adaptations were achieved with a very low weekly training volume. We conclude that vibroX quickly increases muscle (fiber) size, capillarization, and oxidative potential, and markedly augments endurance capacity in young women.

Effects of a 12-week intervention period with football and running for habitually active men with mild hypertension.

The present study examined the effect of football (F, n=15) training on the health profile of habitually active 25-45-year-old men with mild hypertension and compared it with running (R, n=15) training and no additional activity (controls, C, n=17). The participants in F and R completed a 1-h training session 2.4 times/week for 12 weeks. Systolic and diastolic blood pressure decreased in all groups but the decrease in diastolic blood pressure in F (-9 +/- 5 (+/- SD) mmHg) was higher than that in C (-4 +/- 6 mmHg). F was as effective as R in decreasing body mass (-1.6 +/- 1.8 vs-1.5 +/- 2.1 kg) and total fat mass (-2.0 +/- 1.5 vs -1.6 +/- 1.5 kg) and in increasing supine heart rate variability, whereas no changes were detected for C. Maximal stroke volume improved in F (+13.1%) as well as in R (+10.1%) compared with C (-4.9%). Total cholesterol decreased in F (5.8 +/- 1.2 to 5.5 +/- 0.9 mmol/L) but was not altered in R and C. We conclude that football training, consisting of high-intensity intermittent exercise, results in positive effects on blood pressure, body composition, stroke volume and supine heart rate variability, and elicits at least the same cardiovascular health benefits as continuous running exercise in habitually active men with mild hypertension.

Reliability of measurements with Innocor during exercise.

Cardiac output represents the primary determinant of cardiovascular function. Therefore, understanding how cardiac output is regulated during exercise is crucial. A recently developed tool for determining cardiac output is the Innocor rebreathing system, which also incorporates an ergospirometry unit. So far, Innocor's test-retest reliability under exercise conditions has not been determined in healthy participants. Therefore, 15 male and 15 female healthy participants [30.6 y (SD 4.5); 68.0 kg (SD 10.5)] performed 2 test sessions, each consisting of 2 graded exercise tests to volitional exhaustion. We determined intra- and inter-session reliability of cardiac output, oxygen consumption, carbon dioxide output, and ventilation at 130 W and at peak exercise. For cardiac output, we found averaged coefficients of variation ranging from 4.3 (intra-session, 130 W) to 10.0% (inter-session, rest). For oxygen consumption, coefficients of variation ranged from 3.4 (intra-session, peak) to 5.7% (inter-session, peak). Coefficients of variation for carbon dioxide output were between 4.4 (intra-session, peak) and 6.6% (inter-session, peak), and for ventilation between 5.1 (intra-session, 130 W) and 7.0% (intra-session, peak). Innocor delivers safe and reliable measurements of cardiac output, gas exchange, and ventilation. Therefore, Innocor can be used to assess these parameters in exercise physiology studies as well as in performance diagnostics.

Creatine feeding does not enhance intramyocellular glycogen concentration during carbohydrate loading: an in vivo study by 31P- and 13C-MRS

The main aim of this study was to examine the hypothesis that creatine (Cr) feedingenhances myocellular glycogen storage in humans undergoing carbohydrateloading. Twenty trained male subjects were randomly assigned to have their dietssupplemented daily with 252 g of glucose polymer (GP) and either 21 g of Cr (CRGP,n=10) or placebo (PL-GP, n=10) for 5 days. Changes in resting myocellularglycogen and phosphocreatine (PCr) were determined with Magnetic ResonanceSpectroscopy (13C- and 31P-MRS, respectively). After CR-GP, the levels of intramyocellularglycogen increased from 147 ± 13 (standard error) mmol·(kg wet weight-1)to 172 ± 13 mmol·(kg wet weight)-1, while it increased from 134 ± 17 mmol·(kg wetweight)- to 182 ± 17 mmol·(kg wet weight)-1 after PL-GP; the increments in intramyocellularglycogen concentrations were not statistically different. The increment inthe PCr/ATP ratio after CR-GP (+ 0.20 ± 0.12) was significantly different comparedto PL-GP (- 0.34 ± 0.16) (p<0.05). The present results do not support the hypothesisthat Cr loading increases muscle glycogen storage (AU)

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Creatine feeding does not enhance intramyocellular glycogen concentration during carbohydrate loading: an in vivo study by 31P- and 13C-MRS.

The main aim of this study was to examine the hypothesis that creatine (Cr) feeding enhances myocellular glycogen storage in humans undergoing carbohydrate loading. Twenty trained male subjects were randomly assigned to have their diets supplemented daily with 252 g of glucose polymer (GP) and either 21 g of Cr (CR-GP, n = 10) or placebo (PL-GP, n = 10) for 5 days. Changes in resting myocellular glycogen and phosphocreatine (PCr) were determined with Magnetic Resonance Spectroscopy (13C- and 31P-MRS, respectively). After CR-GP, the levels of intramyocellular glycogen increased from 147 +/- 13 (standard error) mmol x (kg wet weight(-1)) to 172 +/- 13 m mol x (kg wet weight)(-1), while it increased from 134 +/- 17 mmol x (kg wet weight)(-) to 182 +/- 17 mmol x (kg wet weight)(-1) after PL-GP; the increments in intramyocellular glycogen concentrations were not statistically different. The increment in the PCr/ATP ratio after CR-GP (+ 0.20 +/- 0.12) was significantly different compared to PL-GP (- 0.34 +/- 0.16) (p < 0.05). The present results do not support the hypothesis that Cr loading increases muscle glycogen storage.

Respiratory muscle training increases cycling endurance without affecting cardiovascular responses to exercise.

We tested whether the increased cycling endurance observed after respiratory muscle training (RMT) in healthy sedentary humans was associated with a training-induced increase in cardiac stroke volume (SV) during exercise, similar to the known effect of endurance training. Thirteen subjects underwent RMT by normocapnic hyperpnea, nine underwent aerobic endurance training (cycling and/or running) and fifteen served as non-training controls. Training comprised 40 sessions performed within 15 weeks, where each session lasted 30 min. RMT increased cycling endurance at 70% maximal aerobic power (Wmax) by 24% [mean (SD) 35.6 (11.9) min vs 44.2 (17.6) min, P < 0.05], but SV at 60% Wmax was unchanged [94 (21) ml vs 93 (20) ml]. Aerobic endurance training increased both SV [89 (24) ml vs 104 (32) ml, P < 0.01] and cycling endurance [37.4 (12.8) min vs 52.6 (16.9) min, P < 0.01]. In the control group, no changes were observed in any of these variables. It is concluded that the increased cycling endurance that is observed after RMT is not due to cardiovascular adaptations, and that the results provide evidence for the role of the respiratory system as an exercise-limiting factor.

Respiratory muscle endurance training in humans increases cycling endurance without affecting blood gas concentrations.

Isolated respiratory muscle endurance training (RMT) can prolong constant-intensity cycling performance. We tested whether RMT affects O2 supply during exercise, i.e. whether the partial pressure of oxygen in arterial blood (Pa,O2) and/or its oxygen saturation (SaO2) are higher during exercise after RMT than before. A group of 28 sedentary subjects were randomly assigned to either an RMT (n = 13) or a control group (n = 15). The RMT consisted of 40x30 min sessions of normocapnic hyperpnoea. The control group did not perform any training. Breathing and cycling endurance time as well as PaO2 and SaO2 during cycling at a constant intensity of 70% maximum power output were measured before and after the RMT or the control period. Mean breathing endurance increased significantly after RMT compared to control [RMT 5.2 (SD 2.9) vs 38.1 (SD 6.8) min, control 6.5 (SD 5.7) vs 6.4 (SD 7.6) min; P < 0.01], as did mean cycling endurance [RMT 35.6 (SD 11.9) vs 44.0 (SD 17.2) min, control 32.8 (SD 11.6) vs 31.4 (SD 14.4) min; P<0.05]. The RMT did not affect PaO2 which ranged from 11.6 to 12.3 kPa (87-92 mmHg), and SaO2 which ranged from 96% to 98% throughout all tests. In conclusion, RMT substantially increased breathing and cycling endurance in sedentary subjects. These changes, however, cannot be attributed to increased O2 supply, as neither PaO2 nor SaO2 were increased during exercise after RMT.

Influence of continuous and discontinuous training protocols on subcutaneous adipose tissue and plasma substrates.

It has been shown that bouts of high-intensity exercise may reduce subcutaneous adipose tissue more than low-intensity exercise. The aim of the present study was to examine if a discontinuous training protocol is more successful in reducing adipose tissue than a continuous endurance training protocol. Fourteen untrained male volunteers were divided into two groups and trained for 10 weeks performing 3 discontinuous or 3 continuous workouts weekly (discontinuous exercise: 25 times 80 s 35% VO2max and 40 s 80% VO2max; continuous exercise: 50 min 50% VO2max). The discontinuous and the continuous training resulted in a similar subcutaneous adipose tissue loss, determined by skinfold measurement, in the leg above the patella (-2.4+/-2.4 and -2.4+/-1.4mm, respectively). The normalised plasma concentrations of free fatty acid, glycerol, beta-hydroxybutyrate, and lactate were similar throughout the final exercise test at the end of the training period. Our data suggested that the discontinuous protocol, selected so that the average intensity was similar to that of the continuous protocol, was not better than the latter in reducing subcutaneous adipose tissue.

Resynthesis of muscle glycogen after soccer specific performance examined by 13C-magnetic resonance spectroscopy in elite players.

The purpose of this study was to examine using 13C-magnetic resonance spectroscopy whether muscle glycogen (Gly) utilized during a simulation of a fatiguing soccer match followed by repeated sprints would be resynthesized during the next 24 h while players consumed their habitual diet. A group of 12 elite young players [mean age 17.5 (SD 0.8) years, mean body mass 68.9 (SD 6.6) kg, mean height 177.0 (SD 5.4) cm] participated in the study. Average muscle Gly content before the simulation was 134 (SD 16) mmol.(kg wet mass)-1 and decreased during the test (P < 0.001) to 80 (SD 29) mmol.(kg wet mass)-1. The value had increased (P < 0.01) to 122 (SD 33) mmol.(kg wet mass)-1 24 h later but it was not significantly different from the value obtained before the soccer test. Dietary analysis of the food intake during the 24 h after the running test revealed that players consumed an average of 2,681 (SD 970) kcal.day-1. Mean daily protein, fat, and carbohydrate (CHO) intakes were 85 (SD 29), 99 (SD 44), and 327 (SD 116) g, respectively. The mean amounts of CHO intake normalised to body mass were 4.8 (SD 1.8) g.(kg body mass)-1. In conclusion, the results of this study showed that despite a CHO intake of less than 5 g.(kg body mass)-1 the habitual diet of soccer players might be sufficient to replenish in 24 h the muscle Gly utilized during soccer specific performance. However, cumulative deficits of about 10% in Gly replenishment as found in the present study might provoke decrements in performance. Thus, players should pay attention to their habitual diets and add more carbohydrates to replenish their daily deficits and perhaps increase their basal levels of intake.

Influence of endurance exercise on respiratory muscle performance.

PURPOSE: During high-intensity, exhaustive, constant-load exercise above 85% of maximal oxygen consumption, the diaphragm of healthy subjects can fatigue. Although a decrease in trans-diaphragmatic pressure is the most objective measure of diaphragmatic fatigue, possible extra-diaphragmatic muscle fatigue would not be detected by this method. The aim of the present study was to investigate the impact of exhaustive, constant-load cycling exercise at different intensities on global respiratory performance determined by the time to exhaustion while breathing against a constant resistance. METHODS: Ten healthy, male subjects performed an exhaustive cycling endurance test at 65, 75, 85, and 95% of peak oxygen consumption (VO2peak). Before cycling (to) as well as at 10 min (t10) and 45 min (t45) after cycling, respiratory performance was determined. RESULTS: Breathing endurance was equivalently reduced after exhaustive cycling at either 65% (8.4 +/- 4.1 min [t0] vs 3.9 +/- 2.8 min [t10]), 75% (9.9 +/- 6.1 vs 4.4 +/- 2.8 min), 85% (9.3 +/- 6.0 vs 3.8 +/- 2.9 min), or 95% VO2peak (8.5 +/- 5.1 vs 4.0 +/- 2.5 min) and, therefore, was independent of exercise intensity. CONCLUSION: This result contradicts previous findings, possibly due to the fact that extra-diaphragmatic muscles are tested in addition to the diaphragm during resistive breathing.

Respiratory muscle endurance training in chronic obstructive pulmonary disease: impact on exercise capacity, dyspnea, and quality of life.

Inspiratory muscle training may have beneficial effects in certain patients with chronic obstructive pulmonary disease (COPD). Because of the lack of a home training device, normocapnic hyperpnea has rarely been used as a training mode for patients with COPD, and is generally considered unsuitable to large-scale application. To study the effects of hyperpnea training, we randomized 30 patients with COPD and ventilatory limitation to respiratory muscle training (RMT; n = 15) with a new portable device or to breathing exercises with an incentive spirometer (controls; n = 15). Both groups trained twice daily for 15 min for 5 d per week for 8 wk. Training-induced changes were significantly greater in the RMT than in the control group for the following variables: respiratory muscle endurance measured through sustained ventilation (+825 +/- 170 s [mean +/- SEM] versus -27 +/- 61 s, p < 0.001), inspiratory muscle endurance measured through incremental inspiratory threshold loading (+58 +/- 10 g versus +21.7 +/- 9.5 g, p = 0.016), maximal expiratory pressure (+20 +/- 7 cm H(2)O versus -6 +/- 6 cm H(2)O, p = 0.009), 6-min walking distance (+58 +/- 11 m versus +11 +/- 11 m, p = 0.002), V O(2peak) (+2.5 +/- 0.6 ml/kg/min versus -0.3 +/- 0.9 ml/kg/min, p = 0.015), and the SF-12 physical component score (+9.9 +/- 2.7 versus +1.8 +/- 2.4, p = 0.03). Changes in dyspnea, maximal inspiratory pressure, treadmill endurance, and the SF-12 mental component score did not differ significantly between the RMT and control groups. In conclusion, home-based respiratory muscle endurance training with the new device used in this study is feasible and has beneficial effects in subjects with COPD and ventilatory limitation.

Breathing pattern and exercise endurance time after exhausting cycling or breathing.

The aim of the present study was to investigate whether the changes in breathing pattern that frequently occur towards the end of exhaustive exercise (i.e., increased breathing frequency, fb, with or without decreased tidal volume) may be caused by the respiratory work itself rather than by leg muscle work. Eight healthy, trained subjects performed the following three sessions in random order: (A) two sequential cycling endurance tests at 78% peak O2 consumption (VO2peak) to exhaustion (A1, A2); (B) isolated, isocapnic hyperpnea (B1) at a minute ventilation (VE) and an exercise duration similar to that attained during a preliminary cycling endurance test at 78% VO2peak, followed by a cycling endurance test at 78% VO2peak (B2); (C) isolated, isocapnic hyperpnea (C1) at a VE at least 20% higher than that of the preliminary cycling test and the same exercise duration as the preliminary cycling test, followed by a cycling endurance test at 78% VO2peak (C2). Neither of the two isocapnic hyperventilation tasks (B1 or C1) affected either the breathing pattern or the endurance times of the subsequent cycling tests. Only cycling test A2 was significantly shorter [mean (SD) 26.5 (8.3) min] than tests A1 [41.0(9.0) min], B2 [41.9 (6.0) min], and C2 [42.0 (7.5) min]. In addition, compared to test A1, only the breathing pattern of test A2 was significantly different [i.e., VE: + 10.5 (7.6) 1 min(-1), and fb: + 12.1 (8.5) breaths min(-1)], in contrast to the breathing patterns of cycling tests B2 [VE: -2.5 (6.2) 1 min(-1), f(b): +0.2 (3.6) breaths min(-1)] and C2 [VE: -3.0 (7.0) 1 min(-1), fb: +0.6 (6.1) breaths min(-1)]. In summary, these results suggest that the changes in breathing pattern that occur towards the end of an exhaustive exercise test are a result of changes in the leg muscles rather than in the respiratory muscles themselves.

[Nutrition in long physical endurance events]. / Ernährung bei Langzeitausdauerleistungen.

In recent years, there was a trend towards longlasting endurance events. The longer the competitions last, the more important nutrition and fluid replacement will be before, during, and after a race, because an inadequate supply reduces performance. Therefore, we summarize in this review the importance of carbohydrate and fat as well as the substitution of water and electrolytes concerning races of more than 4 hours duration.

Noninvasive measurement of muscle high-energy phosphates and glycogen concentrations in elite soccer players by 31P- and 13C-MRS.

PURPOSE: The purpose of this study was to measure noninvasively the absolute concentrations of muscle adenosine triphosphate [ATP], phosphocreatine [PCr], inorganic phosphate (Pi), and glycogen [Gly] of elite soccer players. METHODS: Magnetic resonance spectroscopy (31P- and 13C-MRS) was used to measure the concentrations of metabolites in the calf muscles of 18 young male players [age = 17.5 +/- 1.0 (SD) yr]. RESULTS: Average muscle [PCr] and [ATP] were 17.8 +/- 3.3 and 6.0 +/- 1.2 mmol x (kg wet weight)(-1), respectively. The ratios of Pi/PCr and PCr/ATP were 0.15 +/- 0.05 and 3.00 +/- 0.26, respectively. The muscle [Gly] was 144 +/- 54 mmol x (kg wet weight)(-1). There was a high correlation (r = 0.93, P < 0.0001) between muscle ATP and PCr concentrations, but there was no correlation between [Gly] and [PCr] or [ATP]. The concentrations of the different metabolites determined in the present study with noninvasive MRS methods were within the ranges of values reported in human muscle from biochemical analysis of muscle biopsies. CONCLUSION: MRS methods can be utilized to assess noninvasively the muscle energetic status of elite soccer players during a soccer season. The high correlation between ATP and PCr might be indicative of fiber type differences in the content of these two metabolites.

Muscle glycogen degradation during simulation of a fatiguing soccer match in elite soccer players examined noninvasively by 13C-MRS.

PURPOSE: The purpose of this research project was to noninvasively determine individual muscle glycogen [Gly] degradation during a test intended to predict individual fatigue in intense soccer matches. METHODS: The [Gly] of the calf muscles of 17 elite soccer players [age = 17.4 +/- 0.8 (SD)] were measured with 13C-MRS before and after an alternating velocity test to exhaustion. Blood samples were taken before and 3 min after the test for determination of blood metabolites. RESULTS: Average muscle [Gly] was 135 +/- 53 mmol x (kg wet weight)(-1) before and 87 +/- 27 mmol x (kg wet weight)(-1) (P < 0.001) after exhaustion (42 +/- 25 min). There was a high correlation (r = 0.87, P < 0.0001) between muscle [Gly] at rest and net muscle [Gly] utilized. There was also a more moderate correlation (r = 0.62, P < 0.01) between net muscle [Gly] used and time to exhaustion during the soccer-specific test. There was some evidence of correlation (r = 0.42, P = 0.09) between resting [Gly] and time to exhaustion. Plasma lactate increased (P < 0.001) from 0.8 +/- 0.4 before the test to 2.5 +/- 1.0 mmol x L(-1) at exhaustion, whereas ammonia was raised (P < 0.0001) from 44.1 +/- 10.3 to 89.7 +/- 14.9 micromol x L(-1). Similarly, plasma free fatty acids were elevated (P < 0.0001) from 148 +/- 106 to 797 +/- 401 micromol x L(-1), and glycerol was increased (P < 0.0001) from 48.3 +/- 17.7 to 182.2 +/- 61.8 micromol x L(-1). Insulin levels (11.9 +/- 3.7 vs 11.7 +/- 4.8 microU x mL(-1)) remained the same. Creatine kinase levels increased (P < 0.0001) from 486 +/- 501 to 640 +/- 548 micromol x L(-1) after the test. CONCLUSIONS: We conclude that exhaustion during soccer-specific performance is related to the capacity to utilize muscle [Gly]. The results underline the importance of dietary counseling (glycogen loading and resynthesis strategies) and proper training to enhance the glycogen levels and glycogenolytic capacity of the players.

Noninvasive measurement of respiratory muscle performance after exhaustive endurance exercise.

The use of noninvasive techniques to measure respiratory muscle performance after different types of endurance exercise has not been entirely successful, as the results have not consistently indicated diminished performance for similar types of exercise. The aim of the present study was 1) to compare different, noninvasive methods to assess respiratory muscle performance before and after an exhaustive cycling endurance test (which has previously been shown to induce diaphragmatic fatigue) and 2) to determine which of the tests best reflect published results of measurements of diaphragmatic fatigue. Twelve healthy subjects participated in the study and performed three different test series in a random order on three different days. These tests were performed before, and 5, 40 and 75 min after an exhausting task (a cycling endurance run at 85% of maximal oxygen uptake (V'O2,max)). The tests of the three test series were 1) breathing against a constant inspiratory resistance to task failure, 2) determination of 12-min sustained ventilatory capacity, and 3) spirometric and maximal inspiratory and expiratory mouth pressure measurements. The only measurement that was affected by exhaustive cycling was the time to task failure breathing against inspiratory resistance. It was significantly reduced from (mean+/-sD) 364+/-88 s before exercise to 219+/-122 s at 5 min after cessation of exercise. It is concluded that the constant-load resistive breathing test to task failure is the only noninvasive respiratory muscle performance test evaluated in this study which shows a decrease in respiratory muscle performance after exhaustive endurance exercise.

Decreased exercise blood lactate concentrations after respiratory endurance training in humans.

For many years, it was believed that ventilation does not limit performance in healthy humans. Recently, however, it has been shown that inspiratory muscles can become fatigued during intense endurance exercise and decrease their exercise performance. Therefore, it is not surprising that respiratory endurance training can prolong intense constant-intensity cycling exercise. To investigate the effects of respiratory endurance training on blood lactate concentration and oxygen consumption (VO2) during exercise and their relationship to performance, 20 healthy, active subjects underwent 30 min of voluntary, isocapnic hyperpnoea 5 days a week, for 4 weeks. Respiratory endurance tests, as well as incremental and constant-intensity exercise tests on a cycle ergometer, were performed before and after the 4-week period. Respiratory endurance increased from 4.6 (SD 2.5) to 29.1 (SD 4.0) min (P < 0.001) and cycling endurance time was prolonged from 20.9 (SD 5.5) to 26.6 (SD 11.8) min (P < 0.01) after respiratory training. The VO2 did not change at any exercise intensity whereas blood lactate concentration was lower at the end of the incremental [10.4 (SD 2.1) vs 8.8 (SD 1.9) mmol x l(-1), P < 0.001] as well as at the end of the endurance exercise [10.4 (SD 3.6) vs 9.6 (SD 2.7) mmol x l(-1), P < 0.01] test after respiratory training. We speculate that the reduction in blood lactate concentration was most likely caused by an improved lactate uptake by the trained respiratory muscles. However, reduced exercise blood lactate concentrations per se are unlikely to explain the improved cycling performance after respiratory endurance training.

Respiratory muscle fitness and exercise endurance in healthy humans.

New evidence exists that the respiratory muscles may limit exercise performance in healthy humans. Four weeks of isolated respiratory training (30 min normocapnic hyperpnea, 5 d.wk-1 significantly increased the endurance time of respiratory muscles and the endurance time of constant-load bicycle tests in sedentary as well as physically active subjects once respiratory muscles had recovered from the training. Minute ventilation and blood lactate concentration were reduced during post-training exercise. Furthermore, respiratory trained subjects had lost the sensation of breathlessness. Maximal oxygen consumption was not affected by respiratory training. The mechanism by which respiratory training improves overall physical performance is as yet unknown.