Blood metabolite data in response to maximal exercise in healthy subjects

Maximal exercise test with gas exchange measurement evaluates exercise capacities with maximal oxygen uptake (VO(2) max) measurement. Measurements of lactate (L), lactate/pyruvate ratio (L/P) and ammonium (A) during rest, exercise and recovery enhance interpretative power of maximal exercise by incorporating muscular metabolism exploration. Maximal exercise test with gas exchange measurement is standardized in cardiopulmonary evaluations but, no reference data of blood muscular metabolites are available to evaluate the muscular metabolism. We determined normal values of L, L/P and A during a standardized maximal exercise and recovery in 48 healthy sedentary volunteers and compared with results obtained in four patients with exercise intolerance and a mitochondrial disease. In healthy subjects, L, L/P and A rose during exercise. In 98% of them L, L/P or A decreased between the fifth and the fifteenth minutes of recovery. In mitochondrial patients, VO(2) max was normal or low, and L, L/P and A had the same evolution as normal subjects or showed no decrease during recovery. We gave normal L, L/P and A values, which establish references for a maximal exercise test with muscular metabolism exploration. This test is helpful for clinicians in functional evaluation, management and treatment of metabolic myopathy and would be a useful tool in diagnosis of metabolic myopathy.     

Growth hormone secretion in acid-base alterations at rest and during exercise.

1. Seven healthy males were studied during cycle ergometer exercise at 33%, 66% and 90% of VO2 max. on three occasions when NH4C1, NaHCO3 or CaCO3 (as a control substance) were administered in gelatin capsules double blind and in randomized order. Plasma growth hormone (HGH), lactic acid and hydrogen ion concentration ([H+]) were measured at frequent intervals. 2. Ammonium chloride produced highest blood [H+] and NaHCO3 the lowest. These differences were maintained during exercise and in recovery. Plasma lactic acid concentrations were similar at rest. At 66%, 90% VO2 max. and recovery lactic acid was highest with NaHCO3 and lowest with NH4C1. 3. Exercise stimulated HGH secretion in all studies and the elevation was proportional to the intensity of the exercise. NH4C1 caused a variable elevation of HGH at rest and 33% VO2 max. At 66% VO2 max., plasma HGH was significantly elevated to similar concentrations in all studies and, at 90% VO2 max., HGH was highest with NaHCO3. 4. An infusion of sodium L(+)-lactate producing plasma lactate concentrations of 3-5 mmol/l did not influence HGH secretion. 5. Exercise is a physiological stimulus to HGH secretion and the mechanism is independent of blood [H+] and lactate concentrations.     

Effects of graduated compression stockings on cardiovascular and metabolic responses to exercise and exercise recovery in persons with spinal cord injury

OBJECTIVE: To investigate whether reporting blood redistribution by means of graduated elastic stockings affects exercise and postexercise responses in people with spinal cord injury (SCI). DESIGN: Crossover trial. SETTING: Physical medicine and rehabilitation department in France. PARTICIPANTS: Fourteen men with traumatic SCI, grouped according to their level of injury. INTERVENTIONS: Subjects performed 2 maximal wheelchair exercise tests 1 week apart, in random order and under a counter-balanced design. One test was done with and the other without graduated elastic stockings (21 mmHg). MAIN OUTCOME MEASURES: Blood lactate, blood pressure, heart rate, maximal power output, and oxygen consumption (Vo2). RESULTS: Postexercise venous lactate concentration was reduced in SCI subjects with lesion levels below T6 while wearing graduated elastic stockings during both exercise and recovery (10.9+/-3.9 mmol/L vs 12.5+/-4.6 mmol/L, P<.05). There were no significant differences in submaximal and maximal values (heart rate, Vo2, power output) between subjects tested with and without graduated elastic stockings. CONCLUSIONS: Wearing elastic stockings affects postexercise responses by decreasing lactate concentration in well-trained, low-level paraplegic patients after a maximal exercise. The relatively low pressure generated by the stockings may not, however, influence the venous system enough to produce improved performance and cardiovascular responses.     

Maximal oxygen consumption and pulmonary circulation in patients with chronic bronchitis

In order to study the relations between maximal oxygen consumption during exercise (VO2max) and the pulmonary circulation when pulmonary artery pressure (PPA) and pulmonary vascular resistance (PVR) are normal or close to normal, we evaluated twenty-three patients with chronic bronchitis, in stable clinical condition. All these patients performed a progressive exercise test on a bicycle ergometer until exhaustion (VO2max); they were also subjected to right heart catheterization at rest and during light exercise at constant load. In these patients with moderate functional impairment, we observed on average a significant, although weak, correlation (r = -0.52, P less than 0.01) between pulmonary vascular resistance at rest and VO2max. When VO2max exceeded 2 1 min-1, PVR was below 210 dyn s cm-5. From the heart rate during maximal exercise we computed the oxygen pulse (O2Pmax). In eight patients O2Pmax was reduced (less than or equal to 11 ml) with maximal heart rate close to its predicted value; in seven of these subjects PVR was abnormal and Ppa at rest was at least 20 mmHg. Thus it seems that in chronic obstructive bronchitis mild disturbances in pulmonary circulation may be a contributory factor in the limitation of exercise performance, and a maximal exercise test may help to detect pulmonary hypertension in these patients.     

Effect of exercise intensity on oxygen consumption kinetics in non-exercising muscle during exercise

This study examined the effect of exercise intensity on the kinetics of muscle oxygen consumption in non-exercising forearm flexor muscles (VO(2mf)) during exercise. Seven healthy male subjects performed cycling exercise for 60 min at 30% of maximal oxygen consumption (%VO(2max)) and 30 min at 50% VO(2max) on separate days. The VO(2mf) values at rest and during exercise were measured by near-infrared spectroscopy. The VO(2mf) at 30% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 20 min after the beginning of exercise (P<0·05) and remained constant within 1·2- to 1·3-fold over resting value until 60 min during exercise. The VO(2mf) at 50% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 15 min after the beginning of exercise (P<0·05). Subsequently, the VO(2mf) at 50% VO(2max) increased with time to 1·3 ± 0·1-fold over resting value at 20 min after the beginning of exercise and to 1·5 ± 0·2-fold over resting value at 30 min. The VO(2mf) 15-30 min of exercise at 50% VO(2max) was significantly higher than that at 30% VO(2max) (P<0·05). These data suggest that the increase in VO(2mf) has a time lag from the beginning of exercise, and the kinetics of VO(2mf) during exercise differs with exercise intensity. Therefore, we conclude that the kinetics of VO(2mf) during exercise is dependent on exercise intensity.     

Maximal oxygen consumption in patients with lung disease.

A theoretical model for oxygen transport assuming a series linkage of ventilation, diffusion, oxygen uptake by erythrocytes, cardiac output, and oxygen release was used to calculate expected values for maximal oxygen intake (VO2max) of patients with various pulmonary disorders 22 patients with either restrictive or obstructive ventilatory impairment were studied at rest and maximal exercise. When exercise measurements of maximal pulmonary blood flow (QCmax), oxygen capacity, membrane diffusing capacity for CO, pulmonary capillary blood volume, alveolar ventilation, and mixed venous oxygen saturation were employed as input values, predictions of VO2max from the model correlated closely with measured values (r = 0.978). Measured VO2max was 976+/-389 ml/min (45.3+/-13% of predicted normal), and VO2max predicted from the model was 1,111+/-427 ml/min. The discrepancy may in part reflect uneven matching of alveolar ventilation, pulmonary capillary blood flow, and membrane diffusing capacity for CO within the lung; uniform matching is assumed in the model so that mismatching will impair gas exchange beyond our predictions. Although QCmax was less than predicted in most patients (63.6+/-19.6% of predicted) the model suggests that raising QCmax to normal could have raised VO2max only 11.6+/-8.8% in the face of existent impairment of intrapulmonary gas exchange. Since pulmonary functions measured at rest correlated well with exercise parameters needed in the model to predict VO2max we developed a nomogram for predicting VO2max from resting CO diffusing capacity, the forced one second expired volume, and the resting ratio of dead space to tidal volume. The correlation coefficient between measured and predicted VO2max, by using this nomogram, was 0.942.     

Progressive exercise testing in closed head-injured subjects: comparison of exercise apparatus in assessment of a physical conditioning program

Progressive exercise tests were performed on 12 closed head-injured subjects to determine 1) whether results differ when tests are performed on a treadmill, a bicycle ergometer, or mechanical stairs and 2) whether a 3-month general physical conditioning program results in an improvement in exercise performance. The subjects performed progressive exercise tests on each apparatus on entry into a residential transitional rehabilitation program and approximately 3 months later following participation in a physical conditioning program. On both the initial and 3-month exercise tests, maximal oxygen consumption (VO2 max) was significantly greater on the treadmill and the mechanical stairs than on the bicycle ergometer. The mean VO2 max was 74% of the predicted value on the initial exercise test and rose to 85% of the predicted value after the 3-month physical conditioning program. Oxygen consumption per kilogram of body weight at a given power output on a given apparatus showed no statistically significant difference between the initial and 3-month tests, indicating no change in exercise efficiency. On the 3-month test, a statistically significant decrease was noted in heart rate at rest and after the 4-minute period of recovery from maximal exercise on any given apparatus. The data obtained in this study indicate that 1) the treadmill and mechanical stairs are more suitable than the bicycle ergometer for assessing maximal exercise performance and 2) improved physical fitness following a physical conditioning program is associated with an improvement in cardiovascular function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of marihuana on cardiorespiratory responses to submaximal exercise.

Six male chronic marihuana (MH) users exercised on a bicycle ergometer for 15 min at approximately 50% VO2max under 3 conditions: (1) not smoking (control), (2) after smoking MH containing 7.5 mg (-) delta-9-tetrahydrocannabinol, and (3) after smoking placebo marihuana (PL). The MH was administered double-blind in a counterbalanced repeated-measures design. Heart rates (HRs), arterial blood pressures (BPs), pulmonary ventilation (VE), and oxygen uptake (VO2) were measured during exercise and 15 min recovery. PL had no effect on any of the physiologic variables. Smoking MH had no effect on systolic blood pressure (SBP), diastolic blood pressure (DBP), VE, or VO2, but did induce a marked increase in heart rate which persisted throughout exercise and recovery periods, averaging 34% higher than control values at rest, 18% higher during exercise, and up to 50% higher during recovery. MH smoking increased the product of HR x SBP in all circumstances.     

Maximal aerobic power in cerebral palsied wheelchair athletes: validity and reliability.

This study examined the validity and reliability of maximal aerobic power (VO2max) during wheelchair ergometry (WE) in wheelchair athletes with cerebral palsy. Six class 3 and class 4 male athletes with cerebral palsy completed two graded exercise tests to volitional fatigue on a wheelchair ergometer mounted on frictionless rollers. Four athletes were also able to complete two tests of bicycle ergometry (BE). Although the reliability coefficients for the VO2max during the two exercise modes were high (.89 and .93 for the WE and BE tests, respectively), the validity coefficients for this variable (ie, the correlations between WE and BE) were poor (.31 and -.24 for trials 1 and 2, respectively). Examination of the individual data indicated that athletes who used wheelchairs as their primary mode of ambulation had higher VO2max values during WE; whereas, those who used canes or no aids for daily ambulation had higher values on BE. Because of the specificity of the, VO2max response, it is recommended that the primary mode of ambulation be considered when deciding on the testing mode for evaluating the cardiorespiratory fitness of athletes with cerebral palsy.     

Non-invasive measurement of stroke volume during exercise in heart failure patients

The objective of the present study was to determine the variability of the arterio-venous O(2) concentration difference [C(a-v)O(2)] at anaerobic threshold and at peak oxygen uptake (VO(2)) during a progressively increasing cycle ergometer exercise test, with the purpose of assessing the possible error in estimating stroke volume from measurements of VO(2) alone. We sampled mixed venous and systemic arterial blood every 1 min during a progressively increasing cycle ergometer exercise test and measured, in each blood sample, haemoglobin concentration and blood gas data. Ventilation, VO(2) and CO(2) uptake were also measured continuously. We studied 40 patients with normal haemoglobin concentrations and with stable heart failure due to ischaemic or idiopathic cardiomyopathy. Mean values (+/-S.D.) for C(a-v)O(2) were 7.8+/-2.6, 13.0+/-2.4 and 15. 0+/-2.7 ml/100 ml at rest, anaerobic threshold and peak VO(2) respectively. The patients with heart failure were divided into classes according to their peak VO(2). Classes A, B and C contained patients with peak VO(2) values of>20, 15-20 and 10-15 ml.min(-1). kg(-1) respectively. At anaerobic threshold, C(a-v)O(2) was 12.3+/-1. 3, 13.1+/-2.7 and 13.5+/-2.6 ml/100 ml for classes A, B and C respectively (class A significantly different from classes B and C; P<0.05). At peak exercise C(a-v)O(2) was 13.6+/-1.4, 15.6+/-2.5 and 15.4+/-3.2 ml/100 ml for classes A, B and C respectively (class A significantly different from classes B and C; P<0.05). Stroke volume was estimated for each subject using the mean values of the measured C(a-v)O(2) in each functional class and individual values of VO(2) and heart rate using the Fick formulation. The average difference between the stroke volume estimated from mean C(a-v)O(2) and that obtained using the patient's actual C(a-v)O(2) value was 9.2+/-9.7, 1.0+/-8.8 and -0.2+/-6.1 ml at anaerobic threshold, and -1.9+/-11.3, 0.9+/-10.0 and -2.3+/-8.5 ml at peak exercise, in classes A, B and C respectively. Among the various classes, the most precise estimation of stroke volume was observed for class C patients. We conclude that stroke volume during exercise can be estimated with the accuracy needed for most purposes from measurement of VO(2) at the anaerobic threshold and at peak exercise, and from population-estimated mean values for C(a-v)O(2) in heart failure patients.     

Blood hormone and metabolite levels during graded cycle ergometer exercise

To study the effect of the intensity of physical exercise on plasma hormone and metabolite levels, a group of 11 well-conditioned males participated in cycle ergometer exercise. The subjects pedalled at three different work loads, corresponding to 63% of VO2max (duration 10 min), 86% of VO2max (duration 10 min) and maximal work load (tolerated 5-7 min) The increases in blood adrenaline, noradrenaline, growth hormone, cyclic AMP, glycerol and lactate concentrations were remarkably similar and exponentially related to the work load. The concentrations of blood glucose, cortisol and glucagon increased only at maximal work load. Many of these changes in blood metabolite and hormone concentrations seem to be related to the increased sympathetic activity during graded exercise.     

Six weeks of aerobic dance exercise improves blood oxidative stress status and increases interleukin-2 in previously sedentary women

This study evaluated the change in blood oxidative stress, blood interleukin-2, and physical performance following 6 weeks of moderate intensity and duration aerobic dance exercise in 24 sedentary women. Blood samples were collected at rest twice before (baseline) and after the 6-week intervention for analysis of protein hydroperoxide (PrOOH), malondialdehyde (MDA), total anti-oxidant capacity (TAC), and interleukin-2 (IL-2) levels. Maximal treadmill run time (Time(max)) and maximal oxygen consumption (VO(2max)) were also measured. All variables were statistically analyzed with a repeated measurement ANOVA and Tukey post hoc. No differences were noted in any variable during the baseline period (p > 0.05). After aerobic dance exercise, VO(2max), Time(max), TAC and IL-2 were significantly increased, whereas MDA levels were decreased significantly (p < 0.05). PrOOH did not change either between baseline measures or after exercise. It can be concluded that aerobic dance exercise at a moderate intensity and duration can improve physical fitness, decrease MDA, and increase TAC and IL-2 in previously sedentary women.     

Haematological and hormonal responses to dynamic exercise in patients with chronic airway obstruction

The influence of exercise on hormonal and total white blood cells (WBC), lymphocytes (L). Granulocytes (GR), and platelet (P) count responses was studied in: twenty-five patients with chronic airway obstruction (CAO, 47 +/- 1.8 years, mean +/- SEM) and thirteen normal subjects (N, 36 +/- 2.6 years). They performed a submaximal (40 W) and a maximal exercise (VO2max). Arterial blood samples were taken at rest, 40 W, and VO2max. [H+], PaCO2, PaO2 haematocrit (Hct), [Hb], P, total platelet volume (TPV), WBC, GR, L, and total red blood cells (RBC) were measured. At rest, WBC, GR, P and TPV were higher in CAO patients, whilst PaO2 and cortisol were lower. At 40 W, when compared to values obtained at rest, WBC, GR, L, P and TPV were increased in both groups; WBC, GR, P and TPV were higher in CAO patients. VO2max of CAO patients represented 54% of that of controls. At VO2max, Hct, [Hb] and RBC were approximately 10% higher than at rest in both groups, whilst changes were more significant in normals for WBC (CAO = 55%, N = 76%), lymphocytes (CAO = 83%, N = 105%), GR, (CAO = 37%; N = 51%), platelets (CAO = 23%, N = 29%), TPV (CAO = 25.4%, N = 35%), [H+] (CAO = 43%, N = 38%) and ACTH (CAO = 82%, N = 139%). PaO2 and cortisol did not differ between groups. PaCO2 and platelets however, were higher in the CAO group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxygen uptake kinetics during exercise in chronic heart failure: influence of peripheral vascular reserve.

Exercise performance in chronic heart failure is severely impaired, due in part to a peripherally mediated limitation. In addition to impaired maximal exercise capacity, the O(2) uptake (VO(2)) response during submaximal exercise may be affected, with a greater reliance on anaerobiosis leading to early fatigue. However, the response of VO(2) kinetics to submaximal exercise in chronic heart failure has not been studied extensively; in particular, the relationship between oxygen utilization and the peripheral response to exercise has not been studied. The present investigation examined the time-constant (tau, corresponding to 63% of the total response fitted from exercise onset) of the VO(2) kinetics on-response to submaximal exercise and its relationship to maximal peripheral blood flow in patients with chronic heart failure, and compared responses with those in healthy sedentary subjects. Subjects were 10 patients with chronic heart failure (NYHA class II/III). The mean age was 50+/-12 years, with a mean resting left ventricular ejection fraction of 25+/-9%. Controls were 10 age-matched healthy subjects. VO(2(max)) was first determined for all subjects. Repeated transitions from rest to exercise were performed on a cycle ergometer while measuring breath-by-breath responses of VO(2) at a fixed work rate of 50% of VO(2(max)) (heart failure patients and healthy controls) and at a work rate equivalent to the average in heart failure patients (65 W; healthy controls only). On a separate occasion, post-maximal ischaemic exercise calf blood flow was measured (strain-gauge plethysmography).Whereas heart failure subjects displayed a significantly prolonged VO(2) kinetics response at a similar absolute workload (i.e. 65 W), as indicated by a longer tau value (42 s, compared with 22 s in controls; P<0.01), there was no difference in tau at a similar relative work rate [50% of VO(2(max))]. In addition, heart failure subjects demonstrated a lower maximal calf blood flow (P<0.05) than control subjects. These results indicate that patients with heart failure have a prolonged VO(2) kinetics on-response compared with healthy subjects at a similar absolute work rate (i.e. 65 W), but not at a similar relative work rate [50% of VO(2(max))]. Thus, despite a reduced maximal calf blood flow response associated with heart failure, it does not appear that this contributes to an impairment of the submaximal exercise response beyond that explained by a reduced maximal exercise capacity [VO(2(max))].     

Ventilatory mechanics and expiratory flow limitation during exercise in patients with obstructive lung disease

The interrelationships among transpulmonary pressure, flow, and volume during exhausting exercise were studied in 12 males with chronic obstructive lung disease. Expiratory pressure during exercise was compared with flow-limiting pressure (P(max)) measured at rest. In 11 patients, expiratory pressure during exercise exceeded P(max), indicating that ventilation became mechanically inefficient. P(max) values of the patients were lower than those of normal subjects. Evidence of expiratory flow augmentation during exercise was noted in two subjects. Since 10 subjects achieved maximal expiratory flow predicted from flow-volume curves when heart rate was not maximal, we conclude that exercise capacity in most subjects was clearly limited by the deranged ventilatory apparatus. Elevations in mean intrathoracic pressure during exercise also may interfere with venous return and impose an additional limitation.     

Maximum rate of oxygen consumption related to succinate dehydrogenase activity in skeletal muscle fibres of chronic heart failure patients and controls

Previous studies indicate that the low maximum rate of oxygen consumption (VO2max) of chronic heart failure (CHF) patients is not because of impaired pump function of the heart. We hypothesize that VO2 during maximum exercise is determined by the total oxidative capacity of skeletal muscle. VO2max of six controls and 14 CHF patients, New York Heart Association class I-III, was determined using an incremental bicycle ergometer test. Cryostat sections of a biopsy from the quadriceps femoris muscle were incubated for succinate dehydrogenase (SDH) using quantitative histochemistry. VO2max (range: 29 ml O2 kg muscle(-1) min(-1) in a class III patient to 118 ml O2 kg muscle(-1) min(-1) in a control subject) correlates with the mean SDH activity of skeletal muscle fibres (r=0.79 or r=0.81, including or excluding oxygen uptake at rest, respectively; P<0.001). The relationship between VO2max and SDH activity is similar to that determined previously using isolated single muscle fibres and myocardial trabeculae under hyperoxic conditions. From the product of SDH activity and the cross-sectional area of the fibre (i.e. spatially integrated SDH activity), it is possible to calculate the maximum oxygen uptake rate per unit muscle fibre length. This uptake rate is linearly related to the number of capillaries per fibre (r=0.76, P<0.001) in all subjects, suggesting that oxidative capacity of skeletal muscle fibres in CHF patients decreases in proportion to the oxygen supply capacity of the microcirculation.     

White blood cell and hormonal responses to 4300 m altitude before and after intermittent altitude exposure

Recent studies have demonstrated that brief daily IAE (intermittent altitude exposure) was equally as effective as continuous altitude residence in inducing physiological adaptations consistent with altitude acclimatization. Although the positive benefits of IAE have been clearly defined, the potential negative consequences of IAE on health, specifically the immune system, remain undefined. The present study determined the effects of IAE on WBC (white blood cell) and hormonal responses during rest and exercise at 4300 m altitude. Six lowlanders (age, 23+/-2 years; body weight, 77+/-6 kg; values are means+/-S.E.M.) completed a VO(2)max (maximal O(2) uptake) and submaximal cycle ergometer test during a 30-h SL (sea level) exposure and during a 30 h exposure to 4300 m altitude-equivalent once before (PreIAE) and once after (PostIAE) a 3-week period of IAE (4 hxday(-1), 5 daysxweek(-1), 4300 m). The submaximal cycle ergometer test consisted of two consecutive 15-min work bouts at 40% and 70% of altitude-specific VO(2)max. Blood samples were obtained at rest and during both exercise work bouts for measurements of WBC count, leucocyte subset counts, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine). WBC, neutrophil and lymphocyte counts increased significantly (P<0.05) during rest and exercise from SL to PreIAE and decreased (P<0.05) during rest and exercise from PreIAE to PostIAE. Monocyte counts decreased (P<0.05) during rest and exercise from PreIAE to PostIAE, but eosinophil and basophil counts did not change. Cortisol, adrenaline and noradrenaline did not change during rest or exercise from SL to PreIAE or PostIAE, but all increased significantly (P<0.05) from rest during the two work bouts. In conclusion, this type of IAE stimulus did not induce a hormonal stress response and did no harm in terms of activation of the immune system at altitude, as measured by WBC and leucocyte subset counts. This method of pre-acclimatization can therefore be highly recommended for inducing altitude acclimatization without the 'altitude residency' requirement.     

Metabolic changes in muscle on long-term alprenolol therapy.

Muscle biopsies from the vastus muscle were taken at rest and immediately after upright bicycle exercise at 50% of the individual VO2max, before and during 6 wk of alprenolol treatment (200 to 400 mg twice daily) in 6 untrained patients with essential hypertension. Resting muscle concentrations (mmole - kg-1 - wet weight) of glycogen, glucose, lactate, and high-energy phosphates [adenosine triphosphate (ATP) and creatine phosphate (CP)] were not affected by alprenolol treatment, but after 10 min after exercise the glycogenolysis increased and depletion of ATP and CP was enhanced. The relationship between blood and muscle lactate was altered by alprenolol, indicating that alprenolol prevents lactate translocation from the muscle to the blood. The results show that during moderate exercise, leg muscle metabolism is influenced by long-term antihypertensive therapy.     

Short-term correlation properties of R-R interval dynamics at different exercise intensity levels

Methods based on non-linear heart rate (HR) dynamics have been suggested to probe features in HR behaviour that are not easily detected by the traditional HR variability indices. This study tested the hypothesis that analysis of correlation properties of R-R intervals provides useful information on HR fluctuation during exercise. High- (HF) and low-frequency (LF) spectral components and a short-term scaling exponent (alpha1) of HR variability, were analysed for nine healthy subjects at rest, during incremental and steady-state exercise, during atropine infusion and during incremental exercise after atropine administration. During the incremental exercise test alpha1 increased from rest to an intensity level of approximately 40% of VO2max (from 1.07+/-0.24 to 1.50+/-0.25, P<0.001) and thereafter decreased linearly until the end of exercise (from 1.50+/-0.25 to 0.38 +/- 0.10, P<0.001). Atropine infusion increased the scaling exponent alpha1 value from 0.91+/-0.23 to 1.37+/-0.31 (P<0.001). During exercise after atropine infusion, a linear reduction was observed in the scaling exponent alpha1 from 1.37+/-0.23 to 0.25+/-0.08 (P<0.001). Analogous changes in alpha1 were seen during long-term steady-state exercise compared to incremental exercise. Conventional HR variability indices did not show any significant changes during exercise at high exercise intensity levels. alpha1 correlated with the LF/HF ratio at rest (r=0.90, P<0.001), but the correlation was weaker after atropine (r=0.71, P<0.05) and during exercise (e.g. r=0.33, P=NS at the level of 40% of VO2max). In conclusion, incremental exercise test until exhaustion results in bidirectional changes in correlation properties of R-R interval dynamics. These changes can be explained by the intensity of vagal and sympathetic input to the sinus node during the different intensity levels of exercise. Changes in alpha1 values can be detected also in high intensity levels, when the conventional measures of HR variability can not be applied.     

Submaximal exercise in persons with stroke: test-retest reliability and concurrent validity with maximal oxygen consumption

OBJECTIVE: To establish the test-retest reliability and concurrent validity with maximum oxygen consumption (VO2max) for 3 submaximal exercise tests in persons with chronic stroke: (1) submaximal treadmill test, (2) submaximal cycle ergometer test, and (3) 6-minute walk test (6MWT). DESIGN: Prospective study using a convenience sample. SETTING: Free-standing tertiary rehabilitation center. PARTICIPANTS: A volunteer sample of 12 community-dwelling individuals who had a stroke with moderate motor deficits. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Heart rate, blood pressure, and oxygen consumption (VO2) were assessed during the exercise tests. RESULTS: Test-retest reliability was good to excellent for the exercise tests (maximal and submaximal tests). VO2 for all submaximal measures related to VO2max (r range, .66-.80). Neither the 6MWT distance, self-selected gait speed, nor hemodynamic measures related to VO2max. CONCLUSION: The VO2 measures of the submaximal exercise tests had excellent reliability and good concurrent validity with VO2max. Submaximal exercise tests may be a method by which to monitor the effects of interventions after a screening test (eg, symptom-limited graded exercise test, dobutamine stress echocardiograph).