Energy cost and energy sources of a ballet dance exercise in female adolescents with different technical ability

This study evaluated energy cost and energy sources of a ballet exercise (grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level (n = 13) and high-level (n = 12). The overall energy requirement of dance exercise (VO_2eq) was obtained by adding the amount of VO₂ during exercise above resting (aerobic source or VO_2ex) to the VO₂ up to the fast component of recovery (anaerobic alactic source or VO_2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or ) of recovery. VO_2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg⁻¹ in low-level and high-level groups, respectively. VO_2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO_2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO_2al and 12 ± 1% for . In high-level group the remaining fractions were: 18 ± 2 % for VO_2al and 4 ± 1% for . Between two groups, significant differences were found in VO_2ex (P < 0.01), (P < 0.01), and VO_2al (P < 0.05). IAT was 55 and 60% of for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to      

Effects of intermittent hypoxia on the cerebrovascular responses to submaximal exercise in humans

Intermittent hypoxia (IH) has been shown to alter the ventilatory and cardiovascular responses to submaximal exercise; however, the effect of IH on the cerebral blood flow (CBF) response to submaximal exercise has not been determined. This study tested the hypothesis that IH would blunt the CBF response during eucapnic and hypercapnic exercise. Nine healthy males underwent 10 consecutive days of isocapnic IH (oxyhaemoglobin saturation = 80%, 1 h day⁻¹). Ventilatory, cardiovascular, and cerebrovascular responses to cycle exercise (50, 100, and 150 W) were measured before and after IH. Carbon dioxide (5% CO₂), a mediator of CBF during exercise, was administered for 2 min of each exercise stage. Over the 10 days of IH, there was an increase in minute ventilation during the IH exposures (P < 0.05). Although exercise produced increases in middle cerebral artery mean velocity (MCA V _mean), and mean arterial pressure (P < 0.05), there was no effect of IH. Similarly, hypercapnic exercise increased and MCA V _mean (P < 0.05); however, the magnitude of the response was unchanged following IH. Our findings indicate that ten daily hypoxia exposures does not alter the CBF response to submaximal exercise.     

Overall and peripheral ratings of perceived exertion during a graded exercise test to volitional exhaustion in individuals of high and low fitness

This study assessed the relationship between differentiated ratings of perceived exertion (RPE) and heart rate with oxygen uptake during two graded exercise tests (GXT) to exhaustion on a cycle ergometer in 49 men and women (19–50 years) of high and low fitness. The study also assessed whether sub-maximal RPE values elicited during the GXTs could provide appropriate estimates of maximal aerobic power Peripheral RPE (RPE_P) was higher than overall RPE (RPE_O) at exhaustion in both groups (P < 0.001), but the reliability of the terminal RPE_O was higher (0.75 and 0.40, respectively). Fitness did not moderate the relationship of RPE_O and RPE_P with during the GXTs (P > 0.05). However, the correlation for RPE_P and was higher for women compared to men (0.98 and 0.96, respectively, P < 0.05), although this is of little practical significance. In both groups, RPE_O was almost as highly correlated with as heart rate during GXTs terminated at exhaustion (∼0.955–0.980). There were no differences between predicted and measured when values were extrapolated from sub-maximal RPE_O (13, 15 and 17) intensities (42.1 ± 12.5, 43.4 ± 11.5, 44.2 ± 11.3 and 43.3 ± 10.0 ml kg⁻¹ min⁻¹, respectively). However, predicted from sub-maximal RPE_P intensities was significantly lower (P < 0.05). In conclusion, terminal RPE_O was a more reliable measure of the RPE, and provided more accurate estimates of in healthy participants of high and low fitness when elicited from sub-maximal exercise intensities.     

Kinetics of pulmonary \dot{V} \hbox{O}_{2} and femoral artery blood flow and their relationship during repeated bouts of heavy exercise

The mechanism that alters the pulmonary response to heavy-intensity exercise following prior heavy exercise has been frequently ascribed to an improvement in pre-exercise blood flow (BF) or O₂ delivery. Interventions to improve O₂ delivery have rarely resulted in a similar enhancement of However, the actual limb blood flow and dynamics in the second bout of repeated exercise remain equivocal. Seven healthy female subjects (21–32 years) performed consecutive 6-min (separated by 6 min of 10 W exercise) bilateral knee extension (KE) exercise in a semisupine position at a work rate halfway between the lactate threshold (LT) and peak. Femoral artery blood flow (FBF) was measured by Doppler ultrasound simultaneously with breath-by-breath each protocol being repeated at least four times for precise kinetic characterization. The effective time-constant (τ′) of the response was reduced following prior exercise (bout 1: 61.0 ±10.5 vs. bout 2: 51.6±9.0 s; mean ± SD; P<0.05), which was a result of a reduced slow component (bout 1: 16.0±8.0 vs. bout 2: 12.5±6.7 %; P<0.05) and an unchanged ‘primary’ τ. FBF was consistently faster than However, there was no bout-effect on τ′ FBF (bout 1: 28.2±12.0 vs. bout 2: 34.2±8.5 s). The relationship between the exercise-associated (i.e., ) and Δ FBF was similar between bouts, with a tendency (N.S: P>0.05) for to be increased during the transition to bout 2 rather than decreased, as hypothesized. The return of kinetics toward first order, therefore, was associated with an ‘appropriate’, not enhanced, BF to the working muscles. Whether a relative prior-hyperemia in bout 2 enables a more homogeneous intramuscular distribution of BF and/or metabolic response is unclear, however, these data are consistent with events more proximal to the exercise muscle in mediating the response during repeated heavy-intensity KE exercise.     

Prior heavy knee extension exercise does not affect $$\dot{V}\hbox{O}_{2}$$ kinetics during subsequent heavy cycling exercise

This study examined the magnitude of the oxygen uptake slow component during heavy exercise when preceded by heavy knee extension (KE) exercise. Nine males (26.6 ± 1.7 years, ±SE) performed repeated bouts of heavy exercise, each lasting 6 min with 6 min of recovery. Cycling–cycling trials (CYC₁, CYC₂) involved step transitions to a workrate corresponding to 50% of the difference between peak and the lactate threshold (Δ 50%). During bilateral KE-cycling trails (KE, CYC₃), KE was performed at an intensity requiring twofold greater muscle activation relative to CYC₁ followed by a cycling transition to Δ 50%. was measured breath-by-breath and was modeled using three exponentials to determinate the amplitudes (A ₂′, A ₃′) and time constants (τ ₂, τ ₃) of the primary phase and SC. Electromyography (EMG) recorded from the vastus lateralis and medialis was averaged and reported relative to maximal voluntary contraction (%MVC). EMG was higher (p < 0.05) during KE (37.6 ± 8.1 %MVC) than CYC₁ (20.8 ± 1.9 %MVC), CYC₂ (21.6 ± 5.7 %MVC) and CYC₃ (19.8 ± 6.3 %MVC). The amplitude of the SC was lower (p < 0.05) in CYC₂ (197 ± 120 ml min⁻¹) and CYC₃ (163 ± 51 ml min⁻¹) compared to CYC₁ (325 ± 126 ml min⁻¹). No difference in SC was observed between CYC₂ and CYC₃. Although the activation of additional motor units during KE exercise reduced the amplitude of the SC, the decrease was similar to that observed following heavy cycling exercise. Thus, the activation of motor units in excess of those required for the activity does not alter the response during a subsequent bout of exercise.     

Prognostic value of end-tidal CO<Subscript>2</Subscript> pressure during exercise in patients with left ventricular dysfunction

We compared the prognostic power of end-tidal CO₂ pressure (PETCO₂) during exercise, an index of arterial CO₂ pressure, with those of established respiratory gas indexes during exercise testing in patients with left ventricular dysfunction. Seventy-eight consecutive patients with a left ventricular ejection fraction (LVEF) ≤40% were enrolled in the study. All the patients performed a symptom-limited incremental exercise test with respiratory gas measurements. PETCO₂ at peak exercise, peak O₂ uptake (O₂), the ratio of the increase in ventilation to the increase in CO₂ output (E/CO₂ slope), and the ratio of the increase in O₂ to the increase in work rate (∆O₂/∆WR) were measured. PETCO₂ at peak exercise was significantly correlated with peak O₂, E/CO₂ slope and ∆O₂/∆WR. During a prospective follow-up period of 992 ± 570 days, 14 cardiac deaths occurred. As compared to survivors, non-survivors had a significantly lower LVEF, lower PETCO₂ at peak exercise, lower peak O₂, lower ∆O₂/∆WR and a higher E/CO₂ slope. Among these indexes, only PETCO₂ at peak exercise was found to be an independent predictor for cardiac death. PETCO₂ at peak exercise is useful in predicting poor prognosis in patients with left ventricular systolic dysfunction.     

Sex-related differences in evaporative heat loss: the importance of metabolic heat production

We evaluated the hypothesis that different rates of metabolic heat production between sexes, during exercise at the same percentage of maximum oxygen consumption give proportional differences in evaporative heat loss. Seven males and seven females, exercised at 41.3 ± 2.7% for 60-min at 40°C and 30% relative humidity. Whole-body direct air calorimetry measured rate of whole-body evaporative heat loss while metabolic heat production was measured by indirect calorimetry. was greater in males (243 ± 18 W m⁻²) relative to females (201 ± 4 W m⁻²) (P ≤ 0.05) throughout exercise. This was paralleled by a greater at end-exercise in males (207 ± 51 W m⁻²) relative to females (180 ± 3 W m⁻²) (P ≤ 0.05). Differences in metabolic heat production between sexes during exercise at a fixed percentage of give differences in evaporative heat loss. To compare thermoregulatory function between sexes, differences in metabolic heat production must therefore be accounted for.     

The effect of acute simulated moderate altitude on power,performance and pacing strategies in well-trained cyclists

Athletes regularly compete at 2,000–3,000 m altitude where peak oxygen consumption declines ∼10–20%. Factors other than including gross efficiency (GE), power output, and pacing are all important for cycling performance. It is therefore imperative to understand how all these factors and not just are affected by acute hypobaric hypoxia to select athletes who can compete successfully at these altitudes. Ten well-trained, non-altitude-acclimatised male cyclists and triathletes completed cycling tests at four simulated altitudes (200, 1,200, 2,200, 3,200 m) in a randomised, counter-balanced order. The exercise protocol comprised 5 × 5-min submaximal efforts (50, 100, 150, 200 and 250 W) to determine submaximal and GE and, after 10-min rest, a 5-min maximal time-trial (5-minTT) to determine and mean power output (5-minTT_power). declined 8.2 ± 2.0, 13.9 ± 2.9 and 22.5 ± 3.8% at 1,200, 2,200 and 3,200 m compared with 200 m, respectively, P < 0.05. The corresponding decreases in 5-minTT_power were 5.8 ± 2.9, 10.3 ± 4.3 and 19.8 ± 3.5% (P < 0.05). GE during the 5-minTT was not different across the four altitudes. There was no change in submaximal at any of the simulated altitudes, however, submaximal efficiency decreased at 3,200 m compared with both 200 and 1,200 m. Despite substantially reduced power at simulated altitude, there was no difference in pacing at the four altitudes for athletes whose first trial was at 200 or 1,200 m; whereas athletes whose first trial was at 2,200 or 3,200 m tended to mis-pace that effort. In conclusion, during the 5-minTT there was a dose–response effect of hypoxia on both and 5-minTT_power but no effect on GE.     

Circulatory “Efficacy” during progressive aerobic exercise in children: insights from the <Emphasis Type="Italic">Q</Emphasis>: <Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript> relationship

The relationship between circulatory flow (Q) and oxygen uptake ( ) may provide insights into performance of peripheral mechanisms which govern blood flow during exercise (circulatory efficacy). This study evaluated the response of Q relative to during progressive upright cycle exercise in a group of 39 preadolescent boys (mean age 12.2 ± SD 0.5 years). The Q– relationship was curvilinear, best described by the cubic equation Q = 3.60()³ + 5.24()² + 2.40() − 0.94. Circulatory efficacy, defined as the %ΔQ/%Δ × 100, fell from 70.4% between the first two workloads to 49.7% at peak exercise. This decline in circulatory efficacy is consistent with other published data suggesting a decline in skeletal muscle pump function at high intensity workloads. The pattern of change in relationship of Q and during progressive exercise in these children is similar to that observed in studies of adults. This implies that performance of peripheral determinants of circulatory responses to exercise is not affected by biological maturation.     

Effects of pedal frequency on estimated muscle microvascular O2 extraction

An increase in muscle contraction frequency could limit muscle blood flow compromising the matching of and muscle oxygen uptake This study examined the effects of pedal cadence on skeletal muscle oxygenation at low, moderate and peak exercise. Nine healthy subjects [24.7±6.3 years (SD)] performed incremental cycling exercise at 60 and 100 rpm. Pulmonary was measured breath-by-breath and vastus lateralis oxygenation was determined by near-infrared spectroscopy (NIRS). The deoxyhemoglobin signal ([HHb]) from NIRS was used to estimate microvascular O₂ extraction (i.e., [HHb] ∝ ). The and [HHb] for low, moderate and at peak exercise were determined. The at 60 rpm (low=0.64±0.13, moderate=2.03±0.38 and peak=3.39±0.84 l/min) were lower (P<0.01) than at 100 rpm (1.29±0.23, 2.14±0.39 and 3.54±0.88 l/min, respectively). There was a progressive increase in [HHb] from low to peak exercise. However, there was no significant difference (ANOVA, P=0.94) for the 60 (in μM, low=24.0±9.5, moderate=30.5±13.8 and peak=36.7±16.5) and 100 contractions/min (in μM, low=25.7±11.6, moderate=32.1±14.0 and peak=35.4±16.5). We conclude that vastus lateralis O₂ extraction was similar at 60 and 100 cpm, suggesting that the in the microcirculation was not altered and, presumably, no impairment of occurred with the increase in pedal frequency.     

Living high–training low: effect on erythropoiesis and maximal aerobic performance in elite Nordic skiers

The “living high–training low” model (Hi–Lo) may improve aerobic performance in athletes, and the main mechanism of this improvement is thought to be augmented erythropoiesis. A positive effect of Hi–Lo has been demonstrated previously by using altitudes of 2,000–3,000 m. Since the rate of erythropoiesis is altitude-dependent, we tested whether a higher altitude (3,500 m) during Hi–Lo increases erythropoiesis and maximal aerobic performance. Nordic skiers trained for 18 days at 1,200 m, while sleeping at 1,200 m in ambient air (control group, n = 5) or in hypoxic rooms (Hi–Lo, n = 6; 3 × 6 days at simulated altitudes of 2,500, 3,000 and finally 3,500 m, 11 h day⁻¹). Measurements were done before, during (blood samples only) and 2 weeks after the intervention (POST). Maximal aerobic performance was examined from and time to exhaustion (T _exh) at (minimum speed associated with ), respectively. Erythropoietin and soluble transferrin receptor responses were higher during Hi–Lo, whereas reticulocytes did not change. In POST (vs. before): hematological parameters were similar to basal levels, as well as red blood cell volume, being 2.68 ± 0.83 l (vs. 2.64±0.54 l) in Hi–Lo and 2.62±0.57 l (vs. 2.87 ± 0.59 l) in controls. At that time, neither nor T _exh were improved by Hi–Lo, being non-significantly decreased by 2.0% (controls) and 3.7% (Hi–Lo). The present results suggest that increasing the altitude up to 3,500 m during Hi–Lo stimulates erythropoiesis but does not confer any advantage for maximal O₂ transport.     

Ventilation studied with circulatory occlusion during two intensities of exercise

Summary Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in , and . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, and after cuff release. mirrored better than , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.     

Validity of criteria for establishing maximal O<Subscript>2</Subscript> uptake during ramp exercise tests

The incremental or ramp exercise test to the limit of tolerance has become a popular test for determination of maximal O₂ uptake However, many subjects do not evidence a definitive plateau of the -work rate relationship on this test and secondary criteria based upon respiratory exchange ratio (RER), maximal heart rate (HR_max) or blood [lactate] have been adopted to provide confidence in the measured We hypothesized that verification of using these variables is fundamentally flawed in that their use could either allow underestimation of (if, for any reason, a test were ended at a sub-maximal ), or alternatively preclude subjects from recording a valid Eight healthy male subjects completed a ramp exercise test (at 20 W/min) to the limit of tolerance on an electrically braked cycle ergometer during which pulmonary gas exchange was measured breath-by-breath and blood [lactate] was determined every 90 s. Using the most widely used criterion values of RER (1.10 and 1.15), as determined during the ramp test (4.03 ± 0.10 l/min) could be undermeasured by 27% (2.97 ± 0.24 l/min) and 16% (3.41 ± 0.15 l/min), respectively (both P < 0.05). The criteria of HR_max (age predicted HR_max ± 10 b/min) and blood [lactate] (≥8 mM) were untenable because they resulted in rejection of 3/8 and 6/8 of the subjects, most of whom (5/8) had demonstrated a plateau of at These findings provide a clear mandate for rejecting these secondary criteria as a means of validating on ramp exercise tests.     

The validity of predicting maximal oxygen uptake from perceptually regulated graded exercise tests of different durations

The purpose of this study was to assess the validity of predicting maximal oxygen uptake (max) from sub-maximal values elicited during perceptually regulated exercise tests of 2- and 4-min duration. Nineteen physically active men and women (age range 19–23 years) volunteered to participate in two graded exercise tests to volitional exhaustion to measure max (max_GXT), at the beginning and end of a 2-week period, and four incremental, perceptually regulated tests to predict max in the intervening period. Effort production tests comprised 2 × 2-min and 2 × 4-min bouts on a cycle ergometer, perceptually regulated at intensities of 9, 11, 13, 15 and 17 on the Borg 6-20 rating of perceived (RPE) scale, in that order. Individual linear relationships between RPE and for RPE ranges of 9–17, 11–17 and 9–15 were extrapolated to RPE 20 to predict max. The prediction of max was not moderated by gender. Although, max estimated from RPE 9–17 of trial 1 of the 2-min protocol was significantly lower (P < 0.05) than max_GXT and max predicted from the 4-min trials, the max predicted from trial 2 of the 2-min protocol was a more accurate prediction of max_GXT across all trials. The intraclass correlation coefficient (R) was also higher between max_GXT and max predicted from trial 2 of the 2-min protocol compared to both trials in the 4-min protocol (R = 0.95, 0.88 and 0.79, respectively). Similar results were observed for RPE ranges 9–15 and 11–17. Results suggest that a sub-maximal, perceptually guided, graded exercise protocol, particularly of a 2-min duration, provides acceptable estimates of maximal aerobic power, which are not moderated by gender.     

Metabolic and cardiovascular responses during sub-maximal exercise in humans after 14 days of head-down tilt bed rest and inactivity

f _H, SV, [Hb], C_aO₂, O₂, MAP and R _P were measured in 10 young subjects at rest and during exercise at 50, 100 and 150 W before and after 14 days of head-down tilt bed rest (HDTBR) and of ambulatory (AMB) control period. f _H was 18 and 8% higher after HDTBR and AMB, respectively. SV dropped by 15% both after HDTBR and AMB, whereas did not change. After HDTBR, C_aO₂ decreased at rest (−8%) and at 50 W (−5%), whereas O₂ did not change; MAP was 14 and 6% lower at rest and at 100 W and R _P decreased by 23% only at rest. Changes in f _H and SV were larger after HDTBR than after AMB. These results show that, notwhistanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.     

Alveolar oxygen uptake kinetics with step, impulse and ramp exercise in humans

The breath-by-breath of five male subjects (21.2 years ±3.2; 78.8 kg ±5.9; 179.6 cm ±5.8) was measured during a cycling exercise. Starting from a 10 W baseline, the subjects performed (i) ON and OFF step transitions (ST-ON; ST-OFF) to 50, 90, and 130 W; (ii) a ramp (R) exercise with work rate gradually increasing by 20 W min⁻¹; (iii) impulse transitions (I) to 250 and 410 W lasting 10 and 5 s, respectively. The data was modelled using non-linear weighted least square regressions. The amplitudes of the response turned out to be proportional to the input work rate intensities in all the modalities of exercise. Time constants (τ) and time delays (t _d) of ST-ON and R responses were not significantly different, whereas those of ST-OFF were characterised by longer τ values. τ and t _d of I responses turned out to be identical to those of ST-ON when the responses were fitted using a five-component model. These results suggest that: (i) the system controlling alveolar gas exchange behaves linearly when it is forced by ST and R inputs (the ON and OFF phases being considered separate); (ii) the analysis of the I response depends strongly on the models selected to fit the data. The asymmetry between the ON and OFF responses mirrors that found between the splitting and resynthesis rates of phosphocreatine, and these results support the notion that phosphocreatine could be the main controller of the skeletal muscle respiratory turnover in humans.     

Is aerobic endurance a determinant of cardiac autonomic regulation?

The aim of this study was to determine if subjects matched for but with differing aerobic endurance displayed similar heart rate variability (HRV) at rest and heart rate recovery (HRR) after maximal exercise. We hypothesized that the higher the aerobic endurance, the higher the HRV and the faster the HRR. Twenty-eight well trained middle- and long-distance runners (24 men and 4 women) performed a maximal continuous graded exercise test for the determination of maximal oxygen consumption ventilatory threshold (VT), peak treadmill velocity (PTV) and HRR, as well as a test to measure the autonomic regulation of heart rate during supine rest, using HRV analysis. Once both tests were completed, subjects were matched for and assigned to the low endurance or the high endurance group, depending on the %PTV at which VT occurred (81.9 ± 2.9 and 88.3 ± 3.1%PTV for both groups, respectively; P < 0.0001). Contrary to our hypotheses, neither HRV nor HRR parameters were different between groups or associated with aerobic endurance. (59.0±7.3 ml min⁻¹ kg⁻¹) was inversely correlated with ln SDNN (r = −0.44, P < 0.05), ln HF (r = −0.52, P < 0.05), ln LF + HF (r = −0.53, P < 0.05). These results suggest that aerobic endurance is not associated with cardiovascular autonomic control, as measured by HRV and HRR.     

Deterioration of contractile properties of muscle fibres in elderly subjects is modulated by the level of physical activity

Cardiopulmonary kinetics and electromyographic activity (EMG) during exhausting exercise were measured in 8 males performing three maximal combined arm + leg exercises (cA+L). These exercises were performed at different rates of work (mean ± SD; 373 ± 48, 429 ± 55 and 521 ± 102 W) leading to different average exercise work times in all tests and subjects. reached a plateau versus work rate in every maximal cA+L exercise (range 6 min 33 s to 3 min 13 s). The three different exercise protocols gave a maximal oxygen consumption of 4.67 ± 0.57, 4.58 ± 0.52 and 4.66 ± 0.53 l min⁻¹ (P = 0.081), and a maximal heart rate (HR_max) of 190 ± 6, 189 ± 4 and 189 ± 6 beats min⁻¹ (P = 0.673), respectively. Root mean square EMG (EMG_RMS) of the vastus lateralis and the triceps brachii muscles increased with increasing rate of work and time in all three cA+L protocols. The study demonstrates that despite different maximal rates of work, leading to different times to exhaustion, the circulatory adaptation to maximal exercise was almost identical in all three protocols that led to a plateau. The EMG_RMS data showed increased muscle recruitment with increasing work rate, even though the HR_max and was the same in all three cA+L protocols. In conclusion, these findings do not support the theory of the existence of a central governor (CG) that regulates circulation and neuronal output of skeletal muscles during maximal exercise. Thibault Brink-Elfegoun and Hans-Christer Holmberg contributed equally to this article.     

CO2 rebreathing model in COPD: blood-to-gas equilibration

Rebreathing in a closed system can be used to estimate mixed venous and cardiac output, but these estimates are affected by heterogeneity. The purpose of this study was to validate a mathematical model of CO₂ exchange during CO₂ rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial ranging from 28 to 60 mmHg. Rebreathing increased end-tidal by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) estimated distribution of ventilation and blood flow in one high and one low compartment, the ventilation increase and conservation of mass equations to simulate time courses of and Measured and during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted was lower than measured and predicted indicating gas to blood CO₂ flux. Estimates of the ventilatory response to CO₂, quantified as the slope (S) of the ventilation increase versus were inversely related to gas-to-blood disequilibria due to heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO₂ responsiveness. We conclude that a rebreathing model incorporating baseline heterogeneity and BC can simulate gas and blood in patients with COPD, where variations are large and variable.Laboratory of origin: These experiments were performed at the Lovelace Medical Foundation and at New Mexico Resonance in Albuquerque NM.     

The effects of training intensity on muscle buffer capacity in females

We examined changes in muscle buffer capacity (βm_{in vitro}), and the lactate threshold (LT) after 5 weeks of high-intensity interval training (INT) above the LT or moderate-intensity continuous training (CON) just below the LT. Prior to and immediately after training, 16 female subjects performed a graded exercise test to determine and the LT, followed 2 days later by a resting muscle biopsy from the vastus lateralis muscle to determine βm_{in vitro}. Following baseline testing, the subjects were randomly placed into the INT (n=8) or CON training group (n=8). Subjects then performed 5 weeks of cycle training (3 days per week), performing either high-intensity INT (6–10×2 min at 120–140% LT with 1 min rest) or moderate-intensity CON (80–95% LT) training. Total training volume was matched between the two groups. After the training period, both groups had significant improvements in (12–14%; P<0.05) and the LT (7–10%; P<0.05), with no significant differences between groups. The INT group, however, had significantly greater improvements in βm_{in vitro} (25%; 123±5–153±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹; P<0.05) than the CON group (2%; 130±12–133±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹, P>0.05). Our results show that when matched for training volume, high-intensity interval training above the LT results in similar improvements in and the LT, but greater improvements in βm_{in vitro} than moderate-intensity continuous training below the LT. This suggests that training intensity is an important determinant of changes to βm_{in vitro}.