Increasing Work Rate Research Articles

Distribution of Power Output During Cycling

We aim to summarise the impact and mechanisms of work-rate pacing during individual cycling time trials (TTs). Unlike time-to-exhaustion tests, a TT provides an externally valid model for examining how an initial work rate is chosen and maintained by an athlete during self-selected exercise. The selection and distribution of work rate is one of many factors that influence cycling speed. Mathematical models are available to predict the impact of factors such as gradient and wind velocity on cycling speed, but only a few researchers have examined the inter-relationships between these factors and work-rate distribution within a TT. When environmental conditions are relatively stable (e.g. in a velodrome) and the TT is >10 minutes, then an even distribution of work rate is optimal. For a shorter TT (< or = 10 minutes), work rate should be increased during the starting effort because this proportion of total race time is significant. For a very short TT (< or = 2 minutes), the starting effort should be maximal, since the time saved during the starting phase is predicted to outweigh any time lost during the final metres because of fatigue. A similar 'time saving' rationale underpins the advice that work rate should vary in parallel with any changes in gradient or wind speed during a road TT. Increasing work rate in headwind and uphill sections, and vice versa, decreases the variability in speed and, therefore, the total race time. It seems that even experienced cyclists naturally select a supraoptimal work rate at the start of a longer TT. Whether such a start can be 'blunted' through coaching or the monitoring of psychophysiological variables is unknown. Similarly, the extent to which cyclists can vary and monitor work rate during a TT is unclear. There is evidence that sub-elite cyclists can vary work rate by +/-5% the average for a TT lasting 25-60 minutes, but such variability might be difficult with high-performance cyclists whose average work rate during a TT is already extremely high (>350 watts). During a TT, pacing strategy is regulated in a complex anticipatory system that monitors afferent feedback from various physiological systems, and then regulates the work rate so that potentially limiting changes do not occur before the endpoint of exercise is reached. It is critical that the endpoint of exercise is known by the cyclist so that adjustments to exercise work rate can be made within the context of an estimated finish time. Pacing strategies are thus the consequence of complex regulation and serve a dual role: they are both the result of homeostatic regulation by the brain, as well as being the means by which such regulation is achieved. The pacing strategy 'algorithm' is sited in the brain and would need afferent input from interoceptors, such as heart rate and respiratory rate, as well as exteroceptors providing information on local environmental conditions. Such inputs have been shown to induce activity in the thalamus, hypothalamus and the parietal somatosensory cortex. Knowledge of time, modulated by the cerebellum, basal ganglia and primary somatosensory cortex, would also input to the pacing algorithm as would information stored in memory about previous similar exercise bouts. How all this information is assimilated by the different regions of the brain is not known at present.

Confirmation of Treadmill VO2max in Sprinters and Long Distance Runners

A plateau in oxygen uptake (VO2) despite an increase in work rate is often not observed during continuous incremental exercise tests. Indirect criteria including respiratory exchange ratio (R > 1.10) and blood lactate concentration ([La-] > 8.0 mM) are frequently used to confirm maximal oxygen uptake (VO2max) in the absence of a plateau in VO2. Recently, a test to directly confirm VO2peak was developed for healthy males performing cycle ergometry (J Appl Physiol 100: 764-770, 2006). PURPOSE: The purpose of this investigation was to determine whether long distance runners and sprinters routinely display a VO2 plateau during continuous incremental treadmill tests, and if not, whether the highest VO2 observed was in fact VO2max. METHODS: Nine male long distance runners (age 21 ± 1 yrs, VO2max 71.0 ± 2.8 mL·kg−1·min−1) and six male sprinters (age 26 ± 3 yrs, VO2max 55.9 ± 5.8 mL·kg−1·min−1) ran to volitional exhaustion at a constant treadmill speed previously determined to elicit 4 mM blood [La-]. This continuous incremental test consisted of two-minute stages with 2% grade increments. A VO2 plateau was defined as less than half the expected increase in VO2 between the last two completed stages. Following a 15 minute recovery period, subjects performed a constant work rate test to exhaustion at a steeper grade. Data were analyzed by paired-samples t-test. RESULTS: None of the long distance runners and one of the sprinters achieved a plateau on the continuous incremental test. However, by combining the data from the continuous incremental test and the constant work rate test, all subjects exhibited a discontinuous plateau in VO2. Peak VO2 on the continuous incremental test for the long distance runners (70.6 ± 2.8 mL·kg−1·min−1) was not significantly different (P = 0.12) from peak VO2 on the constant work rate test (69.2 ± 2.5 mL·kg−1·min−1). Peak VO2 on the continuous incremental test for the sprinters (55.6 ± 5.9 mL·kg−1·min−1) was not significantly different (P = 0.09) from peak VO2 on the constant work rate test (53.4 ± 5.0 mL·kg−1·min−1). CONCLUSIONS: Trained competitive sprinters and long distance runners do not routinely exhibit a plateau at VO2max during continuous incremental treadmill tests. Peak VO2 on a continuous incremental treadmill test can be directly confirmed as VO2max by performing an additional higher work rate test following a short rest.

Effects of baseline metabolic rate on pulmonary O2 uptake on-kinetics during heavy-intensity exercise in humans

We hypothesised that initiating heavy-intensity exercise from an elevated baseline metabolic rate would result in slower Phase II O2 uptake V(O2) kinetics and a greater overall 'gain' in V(O2) per unit increase in work rate. Seven healthy males performed a series of like-transitions on a cycle ergometer: (1) from light exercise to 'moderate' exercise (80% of the gas exchange threshold, GET; L-->M); (2) from light exercise to 'heavy' exercise (40% of the difference between GET and V(O2) peak; L-->H); (3) from moderate exercise to heavy exercise (M-->H). The Phase II time constant (tau) was significantly (P<0.01) greater in the M-->H condition (48+/-11 s) compared to the L-->M and L-->H conditions (26+/-6 s versus 27+/-4 s, respectively). Moreover, the end-exercise 'gain' values were significantly different between the three conditions (L-->M, 8.1+/-0.7 mL min-1 W-1; L-->H, 9.7+/-0.4 mL min-1 W-1; M-->H, 10.7+/-0.7 mL min-1 W-1; P<0.05). This 'non-linearity' in the pulmonary V(O2) response to exercise might be attributed, at least in part, to differences in the metabolic properties of the muscle fibres recruited in the abrupt transition from a lower to a higher work rate.

Effects of human pregnancy and advancing gestation on respiratory discomfort during exercise

This study examined the effects of human pregnancy and advancing gestation on the intensity of respiratory discomfort (dyspnea) during cycle exercise. Fourteen pregnant women (PG) performed a progressive cycle ergometer exercise test involving 20 W/min increases in work rate to symptom limitation and/or a heart rate of 170-175 beats/min at 19.7+/-1.2 weeks (ENTRY), 28.2+/-0.3 weeks (TM2) and 36.3+/-0.3 weeks (TM3) gestation. Eight, age-matched, sedentary non-pregnant women (CG) were also studied for comparison purposes. Measurements included dyspnea intensity (Borg scale), minute ventilation (VE), breathing pattern and other cardiorespiratory parameters. At peak exercise, neither pregnancy nor advancing gestation had an effect on dyspnea, VE, breathing pattern, oxygen uptake or work rate (p>0.05). VE was significantly greater (by 11 L/min at 100 W) in the PG at TM3 versus CG (p<0.05) at all submaximal work rates. VE also increased progressively from ENTRY to TM2 and TM3 during submaximal exercise. Dyspnea was not significantly different at any submaximal work rate in the PG at TM3 versus CG or with advancing gestation in the PG. In addition, dyspnea at a standardized exercise VE of 40 L/min was not different at TM3 versus ENTRY or in the PG at TM3 versus CG. Neither pregnancy nor advancing gestation were associated with increased respiratory discomfort during strenuous non-weight bearing cycle ergometer exercise, despite substantial increases in VE and progressive mechanical adaptations of the respiratory system to accommodate the increasing size of the gravid uterus.

The reliability of the i-STAT clinical portable analyser

The purpose of this investigation was to assess the reliability of the i-STAT clinical portable analyser and CG(4)(+) cartridge measures of blood pH, partial pressures of O(2) (pO(2)) and CO(2) (pCO(2)), bicarbonate ([HCO(3)(-)]), base excess (BE), total carbon dioxide (TCO(2)), oxygen saturation (sO(2)) and blood lactate ([BLa(-)]) at various exercise intensities. A comparison between [BLa(-)] measured by the i-STAT and the Accusport lactate analysers during an intermittent treadmill run was also undertaken. The technical error of measurement (TEM%) at rest, at moderate (200W) and maximal exercise (V O(2)max) was acceptable (<15%) for all parameters. The intra-class correlation coefficients for each analyte ranged from weak-to-strong across resting (ICC=0.19-0.96) and moderate (ICC=0.30-0.96) exercise intensities. The ICC for all analytes were observed to be strong following maximal intensity exercise (ICC=0.77-0.95). The comparison of the [BLa(-)] measures between the i-STAT and Accusport showed that the difference between measures was acceptable at both low (<4mmolL(-1)) (-0.39+/-0.27mmolL(-1)), moderate to high concentrations (>4mmolL(-1)) (0.58+/-1.22mmolL(-1)), and across all [BLa(-)] data (0.36+/-1.13mmolL(-1)). In conclusion, the i-STAT clinical analyser and CG(4)(+) cartridge provides reliable measures of a number of blood parameters across exercise intensities. The [BLa(-)] measures from the i-STAT analyser are consistent with that of the Accusport lactate analyser.

Increasing Work Rate in Vision Guided Precision Banded Operations

Concerns over the economic and environmental sustainability of farming are leading to an increased interest in techniques to reduce crop protection inputs by better targeting. One way to improve targeting is through physically aligning treatment devices with crop rows. Manual guidance is a difficult and stressful task due to the high concentration required to maintain acceptable tolerances, typically ±25 mm. Under normal farm conditions, global positioning system based technologies are unable to reliably offer this performance. Commercial implement guidance systems based on computer vision have demonstrated that the required accuracy can be achieved. However, working width is limited due to the need to match implements with drill or transplanter width in order to avoid misalignment at the interface between bouts. This paper describes an integrated vision-based system for tracking multiple bouts that has been tested in two example applications. The first was an inter-row hoe for use in cereals with three independently guided 4 m wide sections, each with its own camera, operating on 12 m tramlines. Trials showed that the standard deviation in the lateral position was 10 mm at 10 km h −1 . The second exemplar based on a conventional boom sprayer was a precision band sprayer for vegetables spanning five 4 m wide beds. Trials indicated the standard deviation in lateral position was 22 mm at 12 km h −1 .

Dual Evaluation of Vagal Activity with Exercise Testing

PURPOSE: Heart rate recovery (HRR), a recognized surrogate of vagal activity, has been shown to strongly predict all cause mortality. However, it only takes into account the physiological and autonomic changes that occur after exercise. We postulate that by considering the rate of heart rate increase during the 1st third of exercise and HRR, the prognostic power would be stronger. We therefore developed the heart rate slope (HR slope), denned as the slope of the linear relation between the initial increase in work rate and heart rate (vagal release). With this, our aim was to determine if the HR slope and HRR together have a better prognostic power than wither alone. METHODS: 1,415 consecutive patients undergoing treadmill testing for clinical reasons from 1997 to 2002 were studied. Heart rate and METs estimated from the ramp work rate were calculated during the first 3 minutes and regressed to calculate the HR slope. RESULTS: After a mean follow-up of 2.8± 1.8 years, there were 110 deaths. Age-adjusted HR slope was both univariately and multivariatley predictive of all cause mortality (multivariate HR = 1.24, 95% CI=1.08–1.42, p = 0.04. The combination of an HR slope >30 beats/MET and HRR <22 beats/MET at 2 minutes in recovery was particularly powerful in predicting mortality (hazard ratio 3.9, 95% CI 2.0–7.7, p<0.0001) with an annual mortality of 6.6%.FigureCONCLUSIONS: A dual evaluation of heart rate response to and after recovery from exercise has a better prognostic power than either alone.

Implementing a Mathematical Model to Compare Oxygen Uptake Kinetics During Steady State

Mathematical models of bioenergetic processes permit quantitative evaluation of the responses to exercise. However, validation of experimental programs in steady state conditions is lacking. PURPOSE: The purpose of this study was to validate an experimental protocol using a mathematical model of the human bioenergetic system during sub-maximal steady state conditions. METHODS: Twelve (N=12) non-cyclists, age (21.8 ± 1.4y), and eight (N=8) cyclists, age (30.5±5.7y), acted as subjects. All subjects signed a university approved IRB informed consent prior to testing. Each subject performed a maximal test with increasing work rate every 4 minutes on the cycle ergometer to volitional fatigue. Oxygen consumption (VO2max, ml*kg−1*min−1) was measured using an open spirometry system. All measures were averaged every minute. The steady state VO2 requirements and the oxygen uptake response to a step work input were determined using the mathematical model from the following equations, respectively: VO2 (WR) = VO2 (rest) + VO2(unloaded pedaling) + □.WR; ΔVO2 (t, WR) = AVO2 (WR) [1-e[-(t-td)/□o2]] where VO2(rest) is the oxygen uptake at rest, VO2 (unloaded) is the oxygen uptake increase above rest during unloaded cycling, □ is a conversion factor representing the ratio A VO2/ΔWR in the moderate intensity range above unloaded pedaling, td is the time delay for the appearance of changes in VO2 from the time at which the step change in the input WR was applied, □ is the time taken to reach steady state values. Associations were investigated between actual measures and the mathematical model using a correlation analysis. Significance was set a priori at p ≥0.05. RESULTS: Exercise value means (SD) included the following: VO2 NC (WR) = 48.4 (16.6) ml*kg−1*min−1 for non-cyclists and ΔVO2NC (WR) = 56.4 (24.95) ml*kg−1*min−1 for cyclists; ΔVO2 NC (t, WR) = 6.38 ml*kg−1*min−1 for non-cyclists and ΔVO2 C (t, WR) = 7.44 ml*kg−1*min-−1. The steady state VO2 requirements and the step change oxygen uptake response were compared and plotted as a function of time. The correlation coefficient was found to be r = 0.95. CONCLUSIONS:This study determined the steady state oxygen uptake kinetics at various submaximal work rates between the groups. The experimental protocol was validated using the mathematical model of the human bioenergetic system.

Impairment of physical exercise capacity in healthy postmenopausal women

Healthy postmenopausal women reveal a series of peripheral vascular abnormalities, whose possible consequences on exercise performance has not been yet elucidated. We studied the response to strenuous exercise in 25 postmenopausal women (mean age 50 +/- 3 years) without cardiovascular risk factors or disease through an integrative cardiopulmonary test. In comparison with 25 premenopausal subjects matched for age and biophysical characteristics, postmenopausal women showed a lower maximal workload (P < .01) and maximum VO2 (P < .01), an early anaerobic threshold (P < .05), and a lower ratio between increase of VO2 consumption and work rate (P < .01). Our results suggest that menopause could represent an important concomitant cause in determining an impairment of exercise capacity. The set of cardiopulmonary abnormalities found in the present study seems to identify the peripheral circulation as the limiting system in postmenopausal women experiencing exercise intolerance. Finally, present findings are in favor of an early introduction of postmenopausal hormone replacement therapy.

Work‐rate affects cardiopulmonary exercise test results in heart failure

Cardiopulmonary exercise test (CPET) is used to evaluate patients with chronic heart failure (HF) usually by means of a personalized ramp exercise protocol. Our aim was to evaluate if exercise duration or ramp rate influences the results. Ninety HF patients were studied (peak V (O(2)): >20 ml/min/kg, n=28, 15-20 ml/min/kg, n=39 and <15 ml/min/kg, n=23). Each patient did four CPET studies. The initial study was used to separate the subjects into three groups, according to their exercise capacity. In the remaining studies, work-rate was increased at three different rates designed to have the subjects reach peak exercise in 5, 10 and 15 min from the start of the ramp increase in work-rate, respectively. The order was randomized. The work-rate applied for the total population averaged 22.7+/-8.0, 11.6+/-3.7, 7.5+/-2.9 W/min with effective loaded exercise duration of 5 min and 16 s+/-29 s, 9 min and 43 s+/-49 s and 14 min and 32 s+/-1 min and 12 s for the 5-, 10- and 15-min tests, respectively. Peak V (O(2)) averaged 16.9+/-4.3*, 18.0+/-4.4 and 18.0+/-5.4 ml/min/kg for the 5-, 10- and 15-min tests, (*=p<0.001 vs. 10 min). The shortest test had the lowest peak heart rate and ventilation and highest peak work-rate. Peak V (O(2)) and heart rate were lowest in 5-min tests regardless of HF severity. The DeltaV (O(2))/Deltawork-rate was lowest in 5-min tests and highest in 15-min tests. At all ramp rates, DeltaV (O(2))/Deltawork-rate was lower for the subjects with the lower peak V (O(2)). The V (e)/V (CO(2)) slope and V (O(2)) at anaerobic threshold were not affected by the protocol for any grade of HF. In chronic HF, exercise protocol has a small effect on peak V (O(2)) and DeltaV (O(2))/Deltawork but does not affect V (O(2)) at anaerobic threshold and V (e)/V (CO(2)) slope.

Effects Of Induced Metabolic Alkalosis On Phosphocreatine Kinetics During Moderate And Heavy Forearm Exercise

The effects of induced metabolic alkalosis (ALK) on the regulation and integration of ATP producing pathways during exercise have not been clearly elucidated. PURPOSE To examine the effects of ALK on the rate of skeletal muscle phosphocreatine (PCr) degradation during a step increase in work rate from light to moderate (MOD) then to heavy (HVY) exercise. METHODS Healthy, active male volunteers (n = 10, age = 26±4; mean ± SD) performed a single trial of isotonic wrist flexion (0.5 Hz, 70° ROM) in control (CON) and in ALK (0.3g/kg of NaHCO3, 90 min prior to testing). Prior to the trials, each subject performed an incremental ramped wrist flexion exercise protocol (0.12 W/min) to determine the work rate corresponding to the intracellular pH threshold (IT). The exercise trials consisted of wrist flexion for 9 min at MOD (75% IT) and HVY (125% IT) exercise. Relative [PCr]and intracellular H+ were measured using 31P-MRS. The initial fundamental PCr response was modeled using a mono-exponential equation and non-linear least-squares regression techniques. RESULTS The time constant of PCr degradation (τPCr) during transition to MOD was similar in CON (52±12 s) and ALK (52±17 s). During HVY the τPCr in CON (57±9 s) and ALK (64±14 s) were not different, however, the relative magnitude of the PCr slow component was reduced (p< 0.05) in ALK (0.034±0.031) compared to CON (0.062±0.028). During the final 3 min of HVY exercise, intracellular [H+] was lower (p< 0.05) in ALK (246±117 nmol/l) compared to CON (291±129 nmol/l). CONCLUSIONS Induced alkalosis during dynamic wrist flexion exercise was associated with similar PCr kinetics during the initial fundamental response in MOD and HVY, but the PCr slow component was reduced in ALK, which may be explained by an attenuated rise in intracellular [H+]. Supported by NSERC

Effects Of Induced Metabolic Alkalosis On Phosphocreatine Kinetics During Moderate And Heavy Forearm Exercise

The effects of induced metabolic alkalosis (ALK) on the regulation and integration of ATP producing pathways during exercise have not been clearly elucidated. PURPOSE To examine the effects of ALK on the rate of skeletal muscle phosphocreatine (PCr) degradation during a step increase in work rate from light to moderate (MOD) then to heavy (HVY) exercise. METHODS Healthy, active male volunteers (n = 10, age = 26±4; mean ± SD) performed a single trial of isotonic wrist flexion (0.5 Hz, 70° ROM) in control (CON) and in ALK (0.3g/kg of NaHCO3, 90 min prior to testing). Prior to the trials, each subject performed an incremental ramped wrist flexion exercise protocol (0.12 W/min) to determine the work rate corresponding to the intracellular pH threshold (IT). The exercise trials consisted of wrist flexion for 9 min at MOD (75% IT) and HVY (125% IT) exercise. Relative [PCr]and intracellular H+ were measured using 31P-MRS. The initial fundamental PCr response was modeled using a mono-exponential equation and non-linear least-squares regression techniques. RESULTS The time constant of PCr degradation (τPCr) during transition to MOD was similar in CON (52±12 s) and ALK (52±17 s). During HVY the τPCr in CON (57±9 s) and ALK (64±14 s) were not different, however, the relative magnitude of the PCr slow component was reduced (p< 0.05) in ALK (0.034±0.031) compared to CON (0.062±0.028). During the final 3 min of HVY exercise, intracellular [H+] was lower (p< 0.05) in ALK (246±117 nmol/l) compared to CON (291±129 nmol/l). CONCLUSIONS Induced alkalosis during dynamic wrist flexion exercise was associated with similar PCr kinetics during the initial fundamental response in MOD and HVY, but the PCr slow component was reduced in ALK, which may be explained by an attenuated rise in intracellular [H+]. Supported by NSERC

Fretting wear of Zr-alloy pressure tubes under the combined effects of in-plane and out-of-plane flow-induced vibrations

Proper design and reliable operation of nuclear power generating plants require accurate prediction of fretting wear failure criteria, which include the volumetric wear losses, the maximum wear depth and minimum root radius of the scar. A unique three-axis fretting wear test facility was developed to simulate the in-plane and out-of-plane dynamic characteristics of the bearing pad/pressure tube tribo-system. The fretting wear of Zr–2.5% Nb alloy at 265 °C was investigated. The results showed that the specific wear rate coefficient decreases with the increase of work rate, and is not constant as it is commonly assumed. The increase in the maximum wear depth with the accumulated wear energy was shown to be approximated by a second-order polynomial function. The correlation between the maximum wear depth h max and the minimum root radius R r, has been established, an aspect that has never been investigated before. Examination of the fret scars showed that they can be classified into three types. When the ratio h max/ R r was correlated to h max, the data are contained within a well-defined bell-shaped envelope, which resembles the normal distribution curve.

Dynamic response characteristics of local muscle blood flow regulatory mechanisms in human forearm exercise

We sought to understand the nature of control mechanisms involved in the adaptation of exercising muscle hyperemia. Seven subjects performed rhythmic dynamic forearm exercise under two exercise conditions: small step 1 [step increase from rest to 40% peak forearm vascular conductance (FVC), in ml.min(-1).100 mmHg-1] for 5 min followed by small step 2 (further increase to 80% peak FVC for 5 min), and large step (step increase from rest to 80% peak FVC for 5 min). FVC data were fit with a two- (small step 1) and three-component (small step 2, large step) exponential as appropriate. For the rapid phase I response, FVC dynamic response characteristics (time delay, time constant) were not affected by the magnitude of the work intensity increase when the transition began from rest, but were slower in the 40-80% transition. Rest-80% gain was greater than either rest-40% or 40-80% transitions but represented the same proportion of the phase I + phase II gain across all transitions (57 vs. 56 vs. 57%, respectively, P = 0.975). For the slower phase II response, dynamic response characteristics were not affected by the magnitude of the work intensity increase when initiated from rest. The time constant was not altered when the transition began from exercise vs. rest. We conclude that 1) dynamic response characteristics of exercise hyperemia control mechanisms are not affected by the magnitude of work rate increase when forearm exercise is initiated from rest, 2) phase I but not phase II dynamic response characteristics are sensitive to baseline exercise intensity, and 3) the mechanisms contributing to phase I result in the same relative response magnitude, regardless of the size of the step increase in exercise intensity or the baseline from which it is initiated.

Non-linear cardiac output dynamics during ramp-incremental cycle ergometry

Published literature asserts that cardiac output (Q(.) = V(.) >O(2)x1/C((a-v))O(2)) increases as a linear function of oxygen uptake with a slope of approximately 5-6 during constant work rate exercise. However, we have previously demonstrated that C((a-v))O(2) has a linear relationship as a function of V(.)O(2) during progressively increasing work rate incremental exercise. Therefore, we hypothesized that Q(.) may indeed have a non-linear relationship with respect to V(.)O(2) during incremental, non-steady state exercise. To investigate this hypothesis, we performed five maximal progressive work rate exercise studies in healthy human subjects. Q(.) was determined every minute during exercise using measured breath-by-breath V(.) >O(2), and arterial and pulmonary artery measurements of PO(2), hemoglobin saturation, and content. Q(.) was plotted as a function of V(.) >O(2) and the linear and non-linear (first order exponential and hyperbolic) fits determined for each subject. Tests for linearity were performed by assessing the significance of the quadratic terms added to the linear relation using least squares estimation in linear regression. Linearity was inadequate in all cases (group P<0.0001). We conclude that cardiac output is a non-linear function of V(.)O(2 )during ramp-incremental exercise; the pattern of non-linearity suggests that while the kinetics of Q(.) > are faster than those of V(.) >O(2) they progressively slow as work rate (and V(.) >O(2)) increases.

Mise en œuvre et bilan d’un réentraînement à l’effort à domicile chez 37 patients avec handicap respiratoire

The purpose of this open, prospective, non-controlled study is to evaluate the feasibility and effect of 10 weeks of home-based exercise retraining on a cyclo-ergometer in respiratory patients. 75 patients are consecutively referred. 37 patients, (75% COPD), took part in the programme, 38 (51%) did not. Nine dropped out, five had missing data, therefore the analysis is of 23 patients. There was a significant improvement in Quality of life (CRQ) (p=0,02), in endurance and in work rate on the bicycle (p<0.001). There is a correlation between the increase in work rate on the bicycle and the improvement in quality of life (p=0.01, r=0.5). When the patients are divided according to the level of improvement in work rate on the cycle-ergometer (mild 0 to 10% improvement; moderate 11 to 49% and strong > 50%) we find that only mild improvement is found in those with a low initial work rate. We confirm the effectiveness of home based training, this being feasible in one out of two patients referred. Co-morbidity and the psycho-social situation were the main exclusion factors. The improvement in effort capacity could be an important determinant of quality of life. Cyclo-ergometer could required too great an effort for training more severe patients.

Chemoreflex drive and the dynamics of ventilation and gas exchange during exercise at hypoxia.

We tested the hypothesis that the promotion of hypoxic ventilatory responsiveness (HVR) and/or hypercapnic ventilatory responsiveness (HCVR) mostly acting on the carotid body with a changing work rate can be attributed to faster hypoxic ventilatory dynamics at the onset of exercise. Eleven subjects performed a cycling exercise with two repetitions of 6 minutes while breathing at FIO(2) = 12%. The tests began with unloaded pedaling, followed by three constant work rates of 40%, 60%, and 80% of the subject's ventilatory threshold at hypoxia. Reference data were obtained at the 80% ventilatory threshold work rate during normoxia. Using three inhaled 100% O(2) breath tests, a comparison of hypoxia and normoxia revealed an augmentation of HVR in hypoxia, which then significantly increased proportionally with the increase in work rate. In contrast, HCVR using three inhaled 10% CO(2) breath tests was unaffected by the difference in work rate at hypoxia but did exceed its level at normoxia. The decrease in the half-time of hypoxic ventilation became significant with an increase in work rates and was significantly lower than at normoxia. Using a multiregression equation, HVR was found to account for 63% of the variance of hypoxic ventilatory dynamics at the onset of exercise and HCVR for 9%. O(2) uptake on-kinetics and off-kinetics under hypoxic conditions were significantly slower than under normoxic conditions, whereas they were not altered by the changing work rates at hypoxia. These results suggest that the faster hypoxic ventilatory dynamics at the onset of exercise can be mostly attributed to the augmentation of HVR with an increase in work rates rather than to HCVR. Otherwise, O(2) uptake dynamics are affected by the lower O(2), not by the changing work rates under hypoxic conditions.

SHORT-TERM EXERCISE TRAINING OF SKELETAL MUSCLE

It has previously been recognized that adaptations in response to endurance training occur as early as 5–7 days. PURPOSE To assess the metabolic adaptations associated with short-term training by 31P magetic resonance spectroscopy (MRS) in both young and older subjects. METHODS We studied 6 young (27 ± 4.5 yrs) and 6 older (70 ± 2.7 yrs) healthy sedentary males. We monitored muscle PCr depletions and PCr recovery (τ) from exercise in both normoxia and hyperoxia during plantar flexion exercise on days 0, 3 and 6 of the 6 day exercise training period. RESULTS On day 0 the young subjects had a significantly shorter PCr τ (23 ± 1.3 s) than the older subjects (32 ± 3.8 s). On day 6 maximum work rate increased significantly in both the young (39 ± 5.3%) and older subjects (22 ± 3.7%), however the increase was significantly greater in the younger subjects. In both the young and older subjects PCr depletion was not significantly spared until day 6. PCr τ in normoxia and hyperoxia did not change significantly in either group across the 6 days, and the subject's τ values were not shortened in hyperoxia either before or as a result of the training. CONCLUSION The metabolic adaptations to short-term exercise training appear intact in older subjects, but performance inprovements appear attenuated. The disproportionately large increase in maximal work rate to PCr sparing (especially in the young group), the failure to improve PCr τ in normoxia, and the continued insensitivity in terms of PCr τ to hyperoxia suggest other non metabolic (e.g. neuronal) adaptations may play an important role in the short-term training response and these my be attenuated with age. Supported by NIH HL 17731 and TRDRP 10KT-0335

Relation Between Oscillatory Ventilation at Rest Before Cardiopulmonary Exercise Testing and Prognosis in Patients With Left Ventricular Dysfunction

Although nocturnal Cheyne-Stokes respiration alternating between hyperpnea and hypopnea has been considered a sign of severe heart failure, the clinical status of cardiac patients who exhibit oscillatory ventilation during wakefulness has not been clarified. This study was carried out to determine the relation between oscillatory ventilation during wakefulness and exercise capacity in patients with chronic heart disease. We also evaluated retrospectively whether the presence of oscillatory ventilation influences the long-term prognosis in these patients. A total of 164 patients with left ventricular dysfunction performed a symptom-limited incremental exercise test. Respiratory gas exchange was measured on a breath-by-breath basis throughout the test. Oscillatory ventilation was defined when clear ventilatory oscillation of at least two consecutive cycles was identified at rest before exercise testing and the difference between the peak and nadir of oscillating ventilation was > 30% of the mean value of ventilation. Oscillatory ventilation was noted in 45 of 164 cardiac patients (27%), and the magnitude (mean +/- SD) of oscillation in these patients was 45.5 +/- 16.9%. Patients with oscillatory ventilation had significantly lower left ventricular ejection fraction than those without it (40.7 +/- 12.7% vs 44.9 +/- 11.6%, p < 0.05). However, parameters of exercise capacity such as the peak oxygen uptake (O(2)), the slope of the increase in O(2) relative to the increase in work rate (DeltaO(2)/DeltaWR), and the ratio of the increase in ventilation to the increase in carbon dioxide output (DeltaE/DeltaCO(2)) were not significantly different between the two groups. The mortality rate during 1,797 +/- 599 days of follow-up did not differ between the groups (p = 0.65). Oscillatory ventilation present at rest before cardiopulmonary exercise testing is not significantly related to the peak O(2), DeltaO(2)/DeltaWR, DeltaE/DeltaCO(2), or prognosis in patients with left ventricular dysfunction.

Exercise prescription based upon cardiac vagal activity for middle-aged obese women.

The purposes of this study were to examine a new method to determine exercise intensity for obese people based on the cardiac vagal activity and to determine the effect of this approach on myocardial stress. Forty-three middle aged obese female volunteers (age 43.7+/-6.5 y; height 1.56+/-0.05 m; body mass 66.5+/-9.3 kg; body mass index 27.3+/-2.8 kg m(2); percentage body fat 40.7+/-5.9%). In the first experiment, 43 subjects performed a ramp exercise test on a bicycle ergometer with measurement of ECG and gas exchange parameters. In the second experiment, 11 subjects performed 45 min of constant walking exercise on a treadmill at a level corresponding to exercise intensity determined by vagal activity obtained from a ramp bicycle test. Blood pressure, endothelin 1 (ET-1), catecholamine, atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) were measured before and after exercise. The heart rate variability power decreased with increasing work rate, and changed little after reaching individual-specific work rate. We presumed that vagal activity disappeared at this point and that the heart rate at this exercise intensity was determined as the vagal activity threshold (T(VA)). The results showed a significant positive correlation (r=0.742, P<0.0001) between T(VA) and ventilatory threshold (VT) heart rates, although the mean heart rate of T(VA) (114.3+/-8.5 beats/min) was significantly lower (P<0.001) than that at VT (119.0+/-11.7), suggesting the cardiac vagal withdrawal occurred prior to the onset of lactate acidosis (lactic acid accumulation). Furthermore, exercise intervention experiment at T(VA) indicated that ET-1, catecholamine and BNP levels were not significantly different before and after exercise. However, ANP levels increased significantly after exercise (pre-exercise 18.6+/-5.38 vs post-exercise 44.0+/-24.87 pg/ml, P<0.001), which in turn brought about a significant post-exercise reduction in the blood pressure (SBP 117.6+/-13.7 vs 110.5+/-7.4 mmHg, P<0.05; DBP 78.6+/-6.7 vs 73.5+/-6.6 mmHg, P<0.01). Our data suggest that it is possible to determine the exercise intensity (T(VA)) on the basis of cardiac vagal response. These results also suggest that exercise at T(VA) level is a safe exercise intensity in the light of cardiac stress, and that T(VA) may be recommended for obese people who might possess lower cardiac sympatho-vagal activity.