Constant Work Rate Exercise Research Articles

Heart rate variability during constant work rate exercise at and above the critical power in patients with severe chronic obstructive pulmonary disease

Objective Heart rate variability is useful in evaluating cardiac autonomic balance. We investigated cardiac autonomic modulation in patients with severe chronic obstructive pulmonary disease (COPD) during heavy and very heavy exercise at and above the critical power (CP). Materials and Methods Nine nonhypoxemic patients with COPD (mean forced expiratory volume in 1 second: 1.2 ± 0.5 L; forced expiratory volume in 1 second/forced vital capacity: 37.6 ± 12%) completed an initial incremental exercise test on a cycle ergometer followed by four constant work rate tests to define their CP. In addition, patients underwent a test at their calculated CP for a target of 20 minutes. The CP test plus a test above CP of sufficient duration to allow heart rate variability analysis were studied further. In these tests, R-R interval data were analyzed for variability in the frequency domain before and during exercise. Results Compared with rest, the power of the normalized low-frequency component (nuLF) decreased (73.0 ± 20.9 vs. 54.2 ± 20.1; p = 0.01) and the power of normalized high-frequency component (nuHF) increased (27.0 ± 20.9 vs. 45.8 ± 20.1; p = 0.01) during exercise, resulting in a decrease in LF/HF (4.1 ± 2.3 vs. 1.6 ± 1.2; p = 0.01) suggesting a relative increase in parasympathetic tone during exercise. When compared with exercise at CP, exercise above CP featured significantly higher values for the square root of the mean squared differences of the successive R-R intervals, the baseline width of the minimum square difference triangular interpolation of the highest peak of the histogram of all N-N intervals and the nuHF, as well as significantly lower values for the nuLF and LF/HF. During exercise above and at the CP, both LF and HF negatively correlated with the respiratory rate ( r = −0.76 and r = −0.70, p < 0.005) and the V max/PEF (ratio of end-exercise peak expiratory flow and peak expiratory flow during a forced maneuver at rest) ( r = −0.52 and r = −0.49, p < 0.05). Conclusion The decrease in nuLF and LF/HF with increasing nuHF in very heavy exercise domains suggests that the autonomic balance is shifted toward parasympathetic tone dominance in patients with severe COPD. This correlates with increasing respiratory rate and ventilatory effort (V max/PEF) during heavy and very heavy exercise in COPD patients.

The power–duration relationship of high‐intensity exercise: from mathematical parameters to physiological mechanisms

The power–duration relationship of high‐intensity exercise: from mathematical parameters to physiological mechanisms

Exercise Protocols to Estimate Fatmax and Maximal Fat Oxidation in Children

Consensus on the exercise protocol used to measure Fatmax (exercise intensity corresponding to maximum fat oxidation (MFO)) in children has not been reached. The present study compared Fatmax estimated using the 3 min incremental cycling protocol (3-INC) and a protocol consisting of several 10 min constant work rate exercise bouts (10-CWR) in 26 prepubertal children. Group Fatmax values were the same for 3-INC and 10-CWR (55% VO2peak) and 95% limits of agreement (LoA) were ± 7% VO2peak. Group MFO values were similar between protocols, although 95% LoA were -94 to 113 mg·min-1. While 3-INC provides a valid estimation of Fatmax compared with 10-CWR, caution should be exercised when estimating MFO in prepubertal children.

Muscle fiber recruitment and the slow component of O2uptake: constant work rate vs. all-out sprint exercise

The slow component of pulmonary O(2) uptake (Vo(2)) during constant work rate (CWR) high-intensity exercise has been attributed to the progressive recruitment of (type II) muscle fibers. We tested the following hypotheses: 1) the Vo(2) slow component gain would be greater in a 3-min all-out cycle test than in a work-matched CWR test, and 2) the all-out test would be associated with a progressive decline, and the CWR test with a progressive increase, in muscle activation, as estimated from the electromyogram (EMG) of the vastus lateralis muscle. Eight men (aged 21-39 yr) completed a ramp incremental test, a 3-min all-out test, and a work- and time-matched CWR test to exhaustion. The maximum Vo(2) attained in an initial ramp incremental test (3.97 ± 0.83 l/min) was reached in both experimental tests (3.99 ± 0.84 and 4.03 ± 0.76 l/min for all-out and CWR, respectively). The Vo(2) slow component was greater (P < 0.05) in the all-out test (1.21 ± 0.31 l/min, 4.2 ± 2.2 ml·min(-1)·W(-1)) than in the CWR test (0.59 ± 0.22 l/min, 1.70 ± 0.5 ml·min(-1)·W(-1)). The integrated EMG declined by 26% (P < 0.001) during the all-out test and increased by 60% (P < 0.05) during the CWR test from the first 30 s to the last 30 s of exercise. The considerable reduction in muscle efficiency in the all-out test in the face of a progressively falling integrated EMG indicates that progressive fiber recruitment is not requisite for development of the Vo(2) slow component during voluntary exercise in humans.

The impact of obesity on walking and cycling performance and response to pulmonary rehabilitation in COPD

BackgroundWe examined the influence of overweight and obesity on pulmonary function, exercise tolerance, quality of life and response to pulmonary rehabilitation in COPD.Methods261 patients with COPD were divided into three groups: normal body mass index (BMI), overweight and obese. Baseline and post rehabilitation pulmonary function, 6-min walking test (6MWT), endurance time during a constant workrate exercise test (CET) and St. George's Respiratory Questionnaire (SGRQ) scores were compared between all three classes of BMI.ResultsAt baseline, obese and overweight patients had less severe airflow obstruction compared to normal BMI patients. There was no baseline difference in CET performance or SGRQ scores across BMI classes and 6MWT was reduced in the presence of obesity (p < 0.01). Compared to baseline, post-rehabilitation 6MWT, CET performance and SGRQ scores improved significantly in each group (p < 0.01), but 6MWT was still significantly lower in the presence of obesity.ConclusionsWalking, but not cycling performance was worse in obese patients. This difference was maintained post rehabilitation despite significant improvements. Weight excess may counterbalance the effect of a better preserved respiratory function in the performance of daily activities such as walking. However, obesity and overweight did not influence the magnitude of improvement after pulmonary rehabilitation.

Does a Low-Density Gas Mixture or Oxygen Supplementation Improve Exercise Training in COPD?

Low-density gas mixtures and oxygen (O₂) supplementation are known to improve physical performance and ventilatory adaptation during incremental maximal exercise in COPD. We investigated whether their combined use during intense physical training is also effective in ameliorating exercise tolerance in patients affected by moderate to severe COPD. Thirty patients (FEV₁ < 60% of predicted) underwent a 2-month rehabilitation program. Leg-cycle training was conducted thrice weekly at 80% of the initial peak work rate for at least 20 min breathing room air, a 60% helium and 40% O₂ mixture, or supplemental O₂ (40%) inhaled from a Douglas bag. The study was randomized with a double-blind design. Before and at the end of the training period the subjects were tested for spirometry, arterial gas tension, diffusing lung capacity for CO, and incremental and constant work rate exercise test on a cycle ergometer. Physical training resulted in a significant improvement in peak oxygen consumption and power output (P < .01 for both) and in exercise endurance time (P < .05) independently of the kind of inhaled gas during the rehabilitation program (P ≥ .42). No changes were observed in lung function tests or gas exchange. We concluded that the use of a low-density gas mixture or O₂ supplementation does not contribute to improved exercise performance in patients with moderate to severe COPD without a significantly decreased diffusion lung capacity for CO who are able to tolerate intense physical training.

Age‐ and sex‐related differences in muscle phosphocreatine and oxygenation kinetics during high‐intensity exercise in adolescents and adults

The aim of this investigation was to examine the adaptation of the muscle phosphates (e.g. phosphocreatine (PCr) and ADP) implicated in regulating oxidative phosphorylation, and oxygenation at the onset of high intensity exercise in children and adults. The hypotheses were threefold: primary PCr kinetics would be faster in children than adults; the amplitude of the PCr slow component would be attenuated in children; and the amplitude of the deoxyhaemoglobin/myoglobin (HHb) slow component would be reduced in children. Eleven children (5 girls, 6 boys, 13 +/- 1 years) and 11 adults (5 women, 6 men, 24 +/- 4 years) completed two to four constant work rate exercise tests within a 1.5 T MR scanner. Quadriceps muscle energetics during high intensity exercise were monitored using (31)P-MRS. Muscle oxygenation was monitored using near-infrared spectroscopy. The time constant for the PCr response was not significantly different in boys (31 +/- 10 s), girls (31 +/- 10 s), men (44 +/- 20 s) or women (29 +/- 14 s, main effects: age, p = 0.37, sex, p = 0.25). The amplitude of the PCr slow component relative to end-exercise PCr was not significantly different between children (23 +/- 23%) and adults (17 +/- 13%, p = 0.47). End-exercise [PCr] was significantly lower, and [ADP] higher, in females (18 +/- 4 mM and 53 +/- 16 microM) than males (23 +/- 4 mM, p = 0.02 and 37 +/- 11 microM, p = 0.02), but did not differ with age ([PCr]: p = 0.96, [ADP]: p = 0.72). The mean response time for muscle tissue deoxygenation was significantly faster in children (22 +/- 4 s) than adults (27 +/- 7 s, p = 0.01). The results of this study show that the control of oxidative metabolism at the onset of high intensity exercise is adult-like in 13-year-old children, but that matching of oxygen delivery to extraction is more precise in adults.

Neural Respiratory Drive in Patients with COPD during Exercise Tests

Background: It is unknown whether neural drive is comparable in constant rate and incremental exercise tests. Few data have previously been available to address this question because of the lack of reliable methods to assess neural respiratory drive in patients with chronic obstructive pulmonary disease (COPD). Objectives: The aims of this study are to determine whether neural respiratory drive during constant rate exercise differs from that during incremental exercise and to determine whether neural respiratory drive was maximal at the end of exhaustive exercise tests. Methods: We studied sixteen patients with moderate-severe COPD (mean ± SD FEV₁ 29 ± 10%). Both diaphragmatic electro-myogram (EMG) and transdiaphragmatic pressure were recorded with a combined multipair electrode balloon catheter during incremental and constant (80% of maximal oxygen consumption derived from a prior incremental exercise test) treadmill exercise. Minute ventilation and oxygen uptake were also measured. Results: Root mean square (RMS) of the diaphragmatic EMG increased gradually without a plateau during incremental exercise, whereas the RMS increased initially and reached a plateau during constant work rate exercise. The RMS of the diaphragmatic EMG at the end of exercise was similar for both incremental and constant work rate exercise (176 ± 42 µV vs. 184 ± 39 µV); these values were 70 and 73% of maximal values recorded over the study. Conclusions: The pattern of increase in neural respiratory drive during incremental exercise is different to that observed during constant work rate exercise, but both exercise protocols are terminated when the patients achieve a similar but submaximal drive.

Effect of obesity on constant workrate exercise in hyperinflated men with COPD.

BackgroundChronic obstructive pulmonary disease (COPD) and a high body mass index (BMI) can both affect pulmonary volumes as well as exercise tolerance, but their combined effect on these outcomes is not well known. The aim of this study was to investigate the effects of increased BMI during constant workrate cycle ergometry in patients with COPD.MethodsMen with COPD and hyperinflation were divided according to World Health Organization BMI classification: 84 normal BMI (NBMI), 130 overweight (OW) and 64 obese (OB). Patients underwent spirometric and lung volumes assessment and an incremental cycling exercise test. This was followed by a constant workrate exercise test (CET) at 75% of peak capacity. Inspiratory capacity and Borg dyspnea scores were measured at baseline, during and at the end of CET.Results and discussionFEV1 % predicted was not different across BMI classes. Total lung capacity and functional residual capacity were significantly lower in OB and OW compared to NBMI patients. Peak VO2 in L·min-1 was significantly higher in OB and OW patients than in NBMI patients. CET time was not different across BMI classes (p = 0.11). Changes in lung volumes and dyspnea during CET were not different between BMI categories.ConclusionsOB and OW patients with COPD had a higher peak VO2 than their lean counterparts. Endurance time, dyspnea and changes in lung volumes during CET were similar between BMI categories.

Influence of respiratory pressure support on hemodynamics and exercise tolerance in patients with COPD

Inspiratory pressure support (IPS) plus positive end-expiratory pressure (PEEP) ventilation might potentially interfere with the "central" hemodynamic adjustments to exercise in patients with chronic obstructive pulmonary disease (COPD). Twenty-one non- or mildly-hypoxemic males (FEV(1) = 40.1 +/- 10.7% predicted) were randomly assigned to IPS (16 cmH(2)O) + PEEP (5 cmH(2)O) or spontaneous ventilation during constant-work rate (70-80% peak) exercise tests to the limit of tolerance (T (lim)). Heart rate (HR), stroke volume (SV), and cardiac output (CO) were monitored by transthoracic cardioimpedance (Physioflow, Manatec, France). Oxyhemoglobin saturation was assessed by pulse oximetry (SpO(2)). At similar SpO(2), IPS(16) + PEEP(5) was associated with heterogeneous cardiovascular effects compared with the control trial. Therefore, 11 patients (Group A) showed stable or increased Delta "isotime" - rest SV [5 (0-29) mL], lower DeltaHR but similar DeltaCO. On the other hand, DeltaSV [-10 (-15 to -3) mL] and DeltaHR were both lower with IPS(16) + PEEP(5) in Group B (N = 10), thereby reducing DeltaCO (p < 0.05). Group B showed higher resting lung volumes, and T (lim) improved with IPS(16) + PEEP(5) only in Group A [51 (-60 to 486) vs. 115 (-210 to 909) s, respectively; p < 0.05]. We conclude that IPS(16) + PEEP(5) may improve SV and exercise tolerance in selected patients with advanced COPD. Impaired SV and CO responses, associated with a lack of enhancement in exercise capacity, were found in a sub-group of patients who were particularly hyperinflated at rest.

Hemodynamic and Gas Exchange Effects of Sildenafil in Patients with Chronic Obstructive Pulmonary Disease and Pulmonary Hypertension

Sildenafil, a phosphodiesterase-5 inhibitor, could be useful for treating pulmonary hypertension (PH) in chronic obstructive pulmonary disease (COPD). However, vasodilators may inhibit hypoxic pulmonary vasoconstriction and impair gas exchange in this condition. To assess the acute hemodynamic and gas exchange effects of sildenafil in patients with COPD-associated PH. We conducted a randomized, dose comparison trial in 20 patients with COPD-associated PH. Eleven patients were assigned to 20 mg, and 9 patients to 40 mg, of sildenafil. Pulmonary hemodynamics and gas exchange, including ventilation-perfusion (V(A)/Q) relationships, were assessed at rest and during constant-work rate exercise, before and 1 hour after sildenafil administration. Both sildenafil doses reduced the mean pulmonary arterial pressure (PAP) at rest and during exercise, without differences between them. Overall, PAP decreased -6 mm Hg (95% confidence interval [95% CI], -7 to -4) at rest and -11 mm Hg (95% CI, -14 to -8) during exercise. After sildenafil, Pa(O(2)) decreased -6 mm Hg (95% CI, -8 to -4) at rest because of increased perfusion in units with low V(A)/Q ratio, without differences between doses. No change in Pa(O(2)) (95% CI, -3 to 0.2 mm Hg) or V(A)/Q relationships occurred during exercise after sildenafil. Changes induced by sildenafil in Pa(O(2)) and V(A)/Q distributions at rest correlated with their respective values at baseline. In patients with COPD-associated PH, sildenafil improves pulmonary hemodynamics at rest and during exercise. This effect is accompanied by the inhibition of hypoxic vasoconstriction, which impairs arterial oxygenation at rest. The use of sildenafil in COPD should be done cautiously and under close monitoring of blood gases. Clinical trial registered with www.clinicaltrials.gov (NCT00491803).

Brief Bout of Exercise Alters Gene Expression in Peripheral Blood Mononuclear Cells of Early- and Late-Pubertal Males

Peripheral blood mononuclear cells (PBMCs) are stimulated by exercise and contribute not only to host defense, but also to growth, repair, and disease pathogenesis. Whether PBMC gene expression is altered by exercise in children is not known. Ten early pubertal boys (8-12 y) and 10 late pubertal boys (15-18 y) performed ten 2-min bouts of strenuous, constant work rate exercise with 1-min rest intervals. PBMCs were isolated before and after exercise and microarray (Affymetrix U133 + 2 chips) analyzed. Statistical criterion to identify gene expression changes was less than 5% false discovery rate (FDR) with 95% confidence interval. One thousand two hundred forty-six genes were altered in older boys (517 up, 729 down), but only 109 were altered in the younger group (79 up, 30 down). In older boys, 13 gene pathways (using Expression Analysis Systematic Explorer, p < 0.05) were found (e.g. natural killer cell cytotoxicity, apoptosis). Epiregulin gene expression (EREG, a growth factor involved in wound healing) increased in older boys. In older boys exercise altered genes such as TBX21, GZMA, PGTDR, and CCL5 also play roles in pediatric inflammatory diseases like asthma. Sixty-six genes were changed significantly in both groups. The pattern of PBMC gene expression suggests the initiation of an immunologic "danger" signal associated with a sudden change in energy expenditure.

Clinical relevance of constant power exercise duration changes in COPD

The endurance time during constant high work-rate exercise (t(LIM)) is used to assess exercise capacity in patients with chronic obstructive pulmonary disease and as an outcome measure for pulmonary rehabilitation. Our study was designed to establish the minimum clinically important difference for the t(LIM). t(LIM) was measured in 105 patients (86 males) before and after an 8-week outpatient pulmonary rehabilitation programme. Subjects were asked to identify, from a five-point Likert scale, the perceived change in their exercise performance immediately upon completion of the exercise tests. The scale ranged from "better" to "worse". The mean+/-sd age was 64+/-5 yrs, forced expiratory volume in 1 s (FEV(1)) 47+/-10% and FEV(1)/forced vital capacity 54.7+/-16.3%. Baseline t(LIM) at 75% of the peak work rate was 397+/-184 s, which increased by 62+/-63% after rehabilitation. In subjects who felt their exercise tolerance was "slightly better", the mean improvement was 34% in the relative improvement over the baseline value (95% CI 29-39)% or 101 (86-116) s compared with 121 (109-134)% in those who reported that their exercise tolerance was "better" and 8 (2-14)% in those who felt their exercise tolerance was "about the same". Minimum clinically important improvement for t(LIM) averaged approximately 33% of baseline. Patients were able to distinguish at least one further additional level of benefit at 120% of baseline.

Endogenous opioids modify dyspnoea during treadmill exercise in patients with COPD

Exogenous opioid drugs, such as morphine, relieve breathlessness. The present study hypothesis was that endogenous opioids, released during the stress of exercise, modify dyspnoea in patients with chronic obstructive pulmonary disease. After familiarisation, patients performed an incremental treadmill exercise test followed by constant work on the treadmill for 10 min. At subsequent visits (2 to 3 days apart), patients received two puffs of albuterol, had a catheter placed in an arm vein for removal of blood to measure beta-endorphin immunoreactivity, received normal saline or 10 mg of naloxone intravenously in randomised order, and then performed high-intensity constant work rate exercise on the treadmill. The mean+/-sd age of the 17 patients (eight females and nine males) was 63+/-7 yrs, and post-bronchodilator forced expiratory volume in one second was 50+/-17% predicted. In both conditions, beta-endorphin levels increased three-fold from rest to end-exercise. The regression slope of breathlessness as a function of oxygen consumption (primary outcome), mean ratings of breathlessness throughout exercise and peak ratings of breathlessness were significantly higher with naloxone than normal saline. There were no differences in physiological responses throughout exercise between conditions. In conclusion, endogenous opioids modify dyspnoea during treadmill exercise in patients with chronic obstructive pulmonary disease by apparent alteration of central perception.

Perceived Exertion is Not Necessarily Associated with Altered Brain Activity during Exercise

Previous studies have investigated the relationship between prefrontal cortex activation and perceived exertion during prolonged exercise. However, the effect of perceived exertion on prefrontal cortex activity is confounded by exercise intensity. Therefore, the changes in prefrontal cortex activity in response to perceived exertion remain unclear. The purpose of the present study was to investigate the relationship between the activation (oxygenation) of the prefrontal cortex and perceived exertion during constant work-rate elbow-flexion exercise with or without muscle-spindle stimulation. Ten healthy, right-handed subjects participated in the study. Near-infrared spectroscopy with probes positioned over the prefrontal cortex measured its activation throughout elbow-flexion exercise. Subjects performed sustained elbow-flexion exercise at 25-35% of the maximal voluntary contraction (MVC) with or without muscle-spindle stimulation (vibration), which can decrease perceived exertion. The ratings of perceived exertion were significantly lower during exercise with vibration (Ex-Vib) than during exercise without vibration (Ex) (p<0.05). The oxygenation of the prefrontal cortex during Ex-Vib did not significantly differ from that during Ex (p>0.05). These results indicated that perceived exertion was not necessarily associated with prefrontal cortex activation during exercise.

Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise

The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP], and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age- or sex-related differences were found in the PCr kinetic time constant at the onset (boys, 21+/-4 s; girls, 24+/-5 s; men, 26+/-9 s; women, 24+/-7 s) or offset (boys, 26+/-5 s; girls, 29+/-7 s; men, 23+/-9 s; women 29+/-7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39+/-0.20 mM/s; girls, 1.32+/-0.32 mM/s; men, 2.36+/-1.18 mM/s; women, 1.51+/-0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.

Respiratory muscle unloading improves leg muscle oxygenation during exercise in patients with COPD

Background:Respiratory muscle unloading during exercise could improve locomotor muscle oxygenation by increasing oxygen delivery (higher cardiac output and/or arterial oxygen content) in patients with chronic obstructive pulmonary disease (COPD).Methods:Sixteen non-hypoxaemic...

Locus of Symptom Limitation and Exercise Response to Bronchodilation in Chronic Obstructive Pulmonary Disease

To evaluate the concordance between subjective and objective indices of muscle fatigue during exercise and to assess the significance of the perception of dyspnea and leg fatigue for the exercise response to bronchodilation in chronic obstructive pulmonary disease (COPD). Sixty-eight patients with COPD performed either 2 constant work-rate cycling exercises or 2 endurance shuttle walking tests. These tests were preceded by nebulization of placebo or 500 mug of ipratropium bromide. Changes in forced expiratory volume in 1 second and in endurance time with bronchodilation were measured. Changes in quadriceps twitch force after exercise were evaluated. In addition, the locus of symptom limitation was assessed. Patients who stopped exercising because of leg fatigue showed a larger fall in quadriceps twitch force in comparison with patients who stopped for dyspnea. The proportion of patients who developed contractile fatigue of the quadriceps (postexercise fall in quadriceps twitch force >15% resting value) was substantially smaller in patients stopping exercise because of dyspnea than in those stopping because of leg fatigue or a combination of the 2 symptoms. The locus of symptom limitation modulated the exercise response to bronchodilation; patients stopping exercise because of leg fatigue or a combination of dyspnea/leg fatigue showed a smaller improvement in endurance time to constant work-rate exercise with bronchodilation compared with those stopping because of dyspnea. Patients with COPD reporting leg fatigue as the main exercise-limiting symptom had a smaller increase in endurance time to constant work-rate exercise after bronchodilation compared with those reporting dyspnea as the main limiting symptom.

Can Ventilation–Feedback Training Augment Exercise Tolerance in Patients with Chronic Obstructive Pulmonary Disease?

Exercise-induced dynamic hyperinflation contributes to decreased exercise tolerance in chronic obstructive pulmonary disease (COPD). It is unknown whether respiratory retraining (ventilation-feedback [VF] training) can affect exercise-induced dynamic hyperinflation and increase exercise tolerance. To determine whether patients with COPD would achieve longer exercise duration if randomized to a combination of exercise training plus VF training than either form of training on its own. A total of 64 patients randomized to 1 of 3 groups: VF plus exercise (n = 22), exercise alone (n = 20), and VF alone (n = 22). Exercise duration before and after 36 training sessions and exercise-induced dynamic hyperinflation and respiratory pattern before and after training were measured. In the 49 patients who completed training, duration of constant work-rate exercise was 40.0 (+/- 20.4) minutes (mean +/- SD) with VF plus exercise, 31.5 (+/- 17.3) minutes with exercise alone, and 16.1 (+/- 19.3) minutes with VF alone. Exercise duration was longer in VF plus exercise than in VF alone (P < 0.0001), but did not reach predetermined statistical significance when VF plus exercise was compared with exercise alone (P = 0.022) (because of multiple comparisons, P </= 0.0167 was used for statistical significance). After training, exercise-induced dynamic hyperinflation, measured at isotime, in VF plus exercise was less than in exercise alone (P = 0.014 for between-group changes) and less than in VF alone (P = 0.019 for between-group changes). After training, expiratory time was longer in VF plus exercise training (P < 0.001), and it was not significantly changed in the other two groups. The combination of VF plus exercise training decreases exercise-induced dynamic hyperinflation and increases exercise duration more than VF alone. An additive effect to exercise training from VF was not demonstrated by predetermined statistical criteria.

Muscle phosphocreatine and pulmonary oxygen uptake kinetics in children at the onset and offset of moderate intensity exercise

To further understand the mechanism(s) explaining the faster pulmonary oxygen uptake (p(VO)(2)) kinetics found in children compared to adults, this study examined whether the phase II p(VO)(2) kinetics in children are mechanistically linked to the dynamics of intramuscular PCr, which is known to play a principal role in controlling mitochondrial oxidative phosphorylation during metabolic transitions. On separate days, 18 children completed repeated bouts of moderate intensity constant work-rate exercise for determination of (1) PCr changes every 6 s during prone quadriceps exercise using (31)P-magnetic resonance spectroscopy, and (2) breath by breath changes in p(VO)(2) during upright cycle ergometry. Only subjects (n = 12) with 95% confidence intervals <or=+/-7 s for all estimated time constants were considered for analysis. No differences were found between the PCr and phase II p(VO)(2) time constants at the onset (PCr 23 +/- 5 vs. p(VO)(2) 23 +/- 4 s, P = 1.000) or offset (PCr 28 +/- 5 vs. p(VO)(2) 29 +/- 5 s, P = 1.000) of exercise. The average difference between the PCr and phase II p(VO)(2) time constants was 4 +/- 4 s for the onset and offset responses. Pooling of the exercise onset and offset responses revealed a significant correlation between the PCr and p(VO)(2) time constants (r = 0.459, P = 0.024). The close kinetic coupling between the p(VO)(2) and PCr responses at the onset and offset of exercise in children is consistent with our current understanding of metabolic control and suggests that an age-related modulation of the putative phosphate linked controller(s) of mitochondrial oxidative phosphorylation may explain the faster p(VO)(2) kinetics found in children compared to adults.