EMG spectral shift- and 31P-NMR-determined intracellular pH in fatigued human biceps brachii muscle.

We have simultaneously recorded human biceps brachii intracellular pH, estimated by 31P-NMR, and EMG spectral shift, during isometric contraction and recovery in six subjects. This method allows us to concurrently study several components of muscle fatigue. The results show a clear dissociation between the recovery of intracellular pH, force-generating capacity, and the shift to low frequency of the EMG power spectrum induced by fatiguing exercise.

Alterations in atrial natriuretic peptide gene expression during endurance training in rats.

Spontaneous and experimental rises of intracardiac pressure and/or volume increase the level of atrial natriuretic (ANP) mRNA in rat atrial tissue. There is expanding evidence that ANP synthesis is increased in the ventricle under such conditions. However, little is known with regard to the myocardial ANP synthesis response to physical training. In this study, plasma and atrial immunoreactive ANP concentrations were measured in Sprague-Dawley rats trained on a treadmill and compared to sedentary controls. Atrial natriuretic peptide mRNA was detected in the heart cavities of each group by dot-blot hybridization analysis. Physical training reduced the mean immunoreactive ANP plasma levels from 405 +/- 99 to 303 +/- 45 ng/l (p < 0.05). Immunoreactive ANP in the left atrium was depleted after endurance training, while immunoreactive ANP concentration in the right atrium was unaffected. Physical training resulted in a 70% (p < 0.01) rise in ANP mRNA of the right atrium, while no changes in the other compartments were found. These data indicate that during physical training: ANP mRNA does not increase in ventricles; despite depletion of immunoreactive ANP in the left atrium, no corresponding changes of ANP mRNA are detected; and ANP mRNA increases in the right atrium while its immunoreactive ANP does not. These findings suggest that during chronic exercise the ratio between immunoreactive ANP and ANP gene expression in the atria may be altered.

Hormonal and metabolic changes during exercise in cirrhotic patients.

The metabolic response to exercise was compared in 10 cirrhotic patients (P) in a stable clinical condition and in 6 sedentary, age-matched, normal subjects (C) performing 32 minutes of treadmill exercise with the same constant workload corresponding to three to four times their resting oxygen uptake. Taking indirect calorimetry as reference, respiratory exchanges indicated that cirrhotic patients consumed carbohydrates almost exclusively, unlike the normal controls, who consumed lipids and glucids in about the same proportions (RQ: 0.98 +/- 0.04 v 0.87 +/- 0.04, P less than .0001). In the patients, this carbohydrate path of exercise metabolism lowered glycemia from the resting value of 5.23 +/- 0.16 mmol/L to 4.03 +/- 0.37 mmol/L (P less than .0001) and raised the plasma lactate concentration from 2.08 +/- 0.24 mmol/L at rest to 3.48 +/- 0.32 mmol/L at the eighth minute of exercise (P less than .001), thus suggesting defective liver glyconeogenesis. Fatty free acids and glycerol remained almost constant during exercise, whereas catecholamines increased. Insulin levels were high in patients at rest (67.1 +/- 14.5 U/mL v 15.1 +/- 3.5 U/mL); they declined sharply at the onset of exercise but nevertheless remained high compared to those observed in the controls (P less than .0001). Glucagon increased in exercising patients from 88.3 +/- 21.3 pg/mL to 127.4 +/- 30.6 pg/mL (NS). Esterified plasma carnitine declined in the patients from 13.0 +/- 2.2 mumol/L to 8.6 +/- 1.5 mumol/L (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Size and metabolic properties of fibers in rat fast-twitch muscles after hindlimb suspension.

Hindlimb suspension (HS) results in whole muscle atrophic and metabolic changes that vary in magnitude in different hindlimb muscles. The present study was designed to investigate these effects in single fibers. Fiber type and size and the activities of two metabolic marker enzymes were determined in a deep (close to the bone) and a superficial (away from the bone) region of the medial gastrocnemius (MG) and the tibialis anterior (TA) of control (CON) and 28-day HS adult female rats. Fibers were classified as dark or light adenosinetriphosphatase (ATPase) based on their qualitative staining reaction for myosin ATPase following alkaline preincubation. Fiber area and succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities were determined in tissue sections by use of an image analysis system. After 28 days of HS, the mean body weights of the CON and HS were similar. MG atrophied 28%, whereas TA weight was maintained in the HS. Both dark and light ATPase fibers in the deep region of the MG had smaller cross-sectional areas following HS, with the atrophic response being approximately twice as great in the light ATPase fibers. No significant changes in fiber type composition in either muscle or in fiber sizes in the superficial region of the MG or in either region of the TA were observed. Mean SDH activities of both fiber types were significantly lower in the MG and TA following HS. In contrast, mean GPD activities were either increased or maintained in light and dark ATPase fibers of both muscles in HS. Changes in SDH and GPD activity could not be directly linked to changes in fiber cross-sectional area. In summary, these data suggest an independence of the mechanisms determining muscle fiber size and metabolic adaptations associated with HS.

Effects of sustained exercise on pulmonary clearance of aerosolized 99mTc-DTPA.

The effects of intensive prolonged exercise on the pulmonary clearance rate of aerosolized 99mTc-labeled diethylenetriaminepentaacetate (99mTc-DTPA) and pulmonary mechanics were studied in seven healthy nonsmoking volunteers. 99mTc-DTPA clearance and pulmonary mechanics (lung volumes and compliance) were assessed before and after 75 min of constant-load exercise performed on a treadmill, corresponding to 75% of maximal O2 uptake. Because both clearance measurements were made in similar conditions of pulmonary blood flow, respiratory rate, and tidal volume, changes in clearance rate can be assumed to represent changes of alveolar epithelial permeability. After exercise, total, apical, and basal clearance were significantly increased (P less than 0.01, 0.05, and 0.05, respectively) and the increases in total clearance and tidal volume observed during exercise were significantly correlated (P less than 0.05). In contrast, no significant change was found in pulmonary mechanics. These results show that prolonged intensive exercise induces an increase in epithelial permeability, which appears to be related to the mechanical effects of sustained increased ventilation. Because no change was evidenced in pulmonary volumes or in lung elasticity, our results suggest that this increase may result from alteration of the intercellular tight junctions rather than from a surfactant deficiency.

Surface EMG power spectrum and intramuscular pH in human vastus lateralis muscle during dynamic exercise.

The relationship between intramuscular pH and the frequency components of the surface electromyographic (EMG) power spectrum from the vastus lateralis muscle was studied in eight healthy male subjects during brief dynamic exercise. The studies were carried out in placebo control and metabolic alkalosis induced by oral administration of NaHCO3. At the onset of exercise, blood pH was 0.08 units higher in alkalosis compared with placebo. Muscle lactate accumulation during exercise was higher in alkalosis (32 +/- 5 mmol/kg wet wt) than in placebo (17 +/- 4 mmol/kg wet wt), but no difference in intramuscular pH was found between the two conditions. The EMG power spectrum was shifted toward lower frequencies during fatigue in the control condition (10.1 +/- 0.9%), and these spectral shifts, evaluated from changes in the mean power frequency (MPF) of the EMG power spectrum, were further accentuated in alkalosis (19 +/- 2%). Although the changes in frequency components of EMG correlated with muscle lactate accumulation (r = 0.68, P less than 0.01), no direct relationship with muscle pH was observed. We conclude that alkalosis results in a greater reduction in MPF associated with a higher muscle lactate accumulation. However, the good correlation observed between the two variables is not likely causative, and a dissociation between intramuscular pH and the increase in the low-frequency content of EMG power spectrum appears during muscle fatigue.

Effect of beta-adrenoceptor blockade on renin-aldosterone and alpha-ANF during exercise at altitude.

The renin-aldosterone system may be depressed in subjects exercising at high altitude, thereby preventing excessive angiotensin I (ANG I) and aldosterone levels, which could favor the onset of acute mountain sickness. The role of beta-adrenoceptors in hormonal responses to hypoxia was investigated in 12 subjects treated with a nonselective beta-blocker, pindolol. The subjects performed a standardized maximal bicycle ergometer exercise with (P) and without (C) acute pindolol treatment (15 mg/day) at sea level, as well as during a 5-day period at high altitude (4,350 m, barometric pressure 450 mmHg). During sea-level exercise, pindolol caused a reduction in plasma renin activity (PRA, 2.83 +/- 0.35 vs. 5.13 +/- 0.7 ng ANG I.ml-1.h-1, P less than 0.01), an increase in plasma alpha-atrial natriuretic factor (alpha-ANF) level (23.1 +/- 2.9 (P) vs. 10.4 +/- 1.5 (C) pmol/1, P less than 0.01), and no change in plasma aldosterone concentration [0.50 +/- 0.04 (P) vs. 0.53 +/- 0.03 (C) nmol/1]. Compared with sea-level values, PRA (3.45 +/- 0.7 ng ANG I.ml-1.h-1) and PA (0.39 +/- 0.03 nmol/1) were significantly lower (P less than 0.05) during exercise at high altitude. alpha-ANF was not affected by hypoxia. When beta-blockade was achieved at high altitude, exercise-induced elevation in PRA was completely abolished, but no additional decline in PA occurred. Plasma norepinephrine and epinephrine concentrations tended to be lower during maximal exercise at altitude; however, these differences were not statistically significant. Our results provide further evidence that hypoxia has a suppressive effect on the renin-aldosterone system. However, beta-adrenergic mechanisms do not appear to be responsible for inhibition of renin secretion at high altitude.

Reversal of hypoxia-induced decrease in human cardiac response to isoproterenol infusion.

A decrease in heart rate response to isoproterenol (IP) infusion has been previously described in humans exposed to acute (2-3 days) or chronic (21 days) exposure to altitude hypoxia (J. Appl. Physiol. 65: 1957-1961, 1988). To evaluate this cardiac response in subacute (8 days) hypoxia and to explore its reversal with restoration of normoxia, six subjects received an IP infusion under normoxia (condition N), after 8 days in altitude (4,350 m, condition H8), on the same day in altitude after inhalation of O2 restoring normoxic arterial O2 saturation (SaO2, condition HO), and 6-11 h (condition RN) and 4-5 mo (condition ND) after the return to sea level. Cardiac chronotropic response to IP, evaluated by the mean increase in heart rate from base value (delta HR, min-1), was lower in condition H8 [mean 30 +/- 13 (SD)] than in condition N (50 +/- 14, P less than 0.03); it was slightly higher in condition HO (38 +/- 14) or condition RN (42 +/- 15) than condition H8 but still significantly different from condition N (P less than 0.03), despite normal values of SaO2. delta HR in condition ND (55 +/- 10) returned to base N value. These findings confirm the hypothesis of a hypoxia-induced decrease in cardiac chronotropic function. Two possible mechanisms are suggested: an O2-dependent one, rapidly reversible with recent restoration of normoxia, and a more slowly reversible mechanism, probably a downregulation of the cardiac beta-receptors.

Metabolic and blood catecholamine responses to exercise during alkalosis.

The effects of metabolic alkalosis on muscle lactate accumulation and plasma catecholamine concentrations were studied in six highly trained subjects during short-term ergocycle exercises to exhaustion (375 W). The studies were performed after oral administration of NaHCO3 (alkalosis) and CaCO3 (placebo). There was a significant increase in resting blood pH after NaHCO3 ingestion (7.35 +/- 0.02) compared to placebo (7.27 +/- 0.02). A longer endurance time was achieved during alkalosis (75.3 +/- 8 s) than during control (61.5 +/- 2 s), but similar blood pH and HCO3- levels were found at exhaustion in both treatments. Metabolic alkalosis resulted in higher elevation in muscle lactate concentration (31.7 +/- 4.6 mmol.kg-1 wet weight) compared to control (17 +/- 4 mmol.kg-1 wet weight). Despite longer exercise duration in alkalosis, plasma norepinephrine and epinephrine concentrations at exhaustion were reduced by 30 and 34%, respectively. These results indicate that alkalosis increased muscle lactate accumulation during exhaustive exercise. These changes were associated with a reduced blood catecholamine response to exercise.

The spatial integration effect of surface electrode detecting myoelectric signal.

The spectral properties of surface electrodes used for myoelectric signal detection were investigated using both a theoretical and an experimental approach. On the basis of the theoretical model, the single surface electrode was found to act as a low pass filter depending on the electrode diameter (d) and the fiber conduction velocities (CV). Several dips in the power spectrum were also predicted for varying frequencies depending on d and CV. The mathematical expression of the surface electrode filter was highly consistent with previously demonstrated properties of the single fiber power spectrum. An experimental comparison between myoelectric signals from the vastus lateralis muscle recorded using two electrode pairs with different diameters confirmed this low pass filter effect. However, the dip phenomenon was not observed from experimental data. The practical consequences of the electrode filter effect are discussed with respect to the interpretation of changes in surface myoelectric signal spectrum, particularly when a shift toward the high frequencies is observed.

[Effect of beta-adrenergic receptors blockade on auricular natriuretic factor, aldosterone and renine blood activity during physical exercise]. / Effet du blocage des récepteurs beta-adrénergiques sur le facteur natriurétique auriculaire, l'aldostérone et l'activité rénine plasmatique, au cours d'un exercise physique.

Physical exercise stimulates the renin-angiotensin-aldosterone system. However several factors affect the control of mineralocorticoid secretion. In this study, eight healthy volunteers performed maximal exercise on cycle ergometer after being pretreated for 3 days with placebo (P) or with a non selective beta-blocker (B) (pindolol 15 mg/day). Plasma reinin activity (PRA), aldosterone (ALD), atrial natriuretic factor (ANF), and kalemia (K+) were measured at rest (R) and during exercise until exhaustion (E). (table; see text) These results confirm the role of beta-adrenoceptor activation in the increased PRA during exercise. It appears an exercise-induced increase in plasma ANF which was more elevated in subjects treated with pindolol, but which had no inhibitory effect on ALD secretion in theses conditions. K+ rose during exercise and this hyperkalemia tended to be higher with a beta-blocker. It is suggested that K+ elevation counterbalance both PRA decrease and ANF increase to be responsible for the absence of change in plasma ALD during beta-blockade.

[Cutaneous cholesterol in the young and aged coronary patient]. / Le cholestérol cutané du coronarien jeune et âgé.

Serum cholesterol (ch), its lipoprotein fractions and triglycerides were measured in three populations of proven coronary patients (less than 50 years, n = 56; between 50 and 65 years, n = 56; greater than 65 years, n = 23); the risk factor total ch/HDL ch was calculated. The level of skin cholesterol was also estimated by skin biopsy in each patient and compared to that of three control populations of the same age. The results indicated that 1) there was no significant difference in skin cholesterol of patients with myocardial infarction whatever their age, 2) there was a significant difference (p less than 0,001) with control subjects of the same age except in the over 65 population, 3) the total cholesterol was normal in all three groups, 4) the HDL cholesterol of coronary patients over 50 year old was normal and slightly reduced in younger coronary patients, 5) the ratio total ch/HDL ch was increased in coronary patients under 50, but normal after this age, 6) the triglyceride level was higher in the young coronary patients than in those over 50 years old. Four conclusions are drawn: 1) the total Ch/HDL ch ratio is a good indicator of coronary risk in patients under 50 years old but shows less sensitive variations than the level of skin cholesterol, 2) the ch/HDL ch in coronary patients between 50 and 65 years old is normal; the only laboratory finding which correlates with the coronary event is skin cholesterol; after 65 years of age the skin cholesterol stabilises to the same levels as found in control subjects; 3) from the outset, at whatever age infarction occurs, skin cholesterol is increased (about 0,45 mumol/100 ngr of fresh skin), whilst the risk factor is higher in the younger population; 4) skin cholesterol shows less variation in the three coronary groups than the other blood parameters measured. It would therefore appear to be a very discriminating index of coronary atherosclerosis.

Oxygen consumption, lactate accumulation, and sympathetic response during prolonged exercise under hypoxia.

Six men (33 +/- 3 years old) performed 1 h ergocycle exercise (60% VO2 max) at sea level and at a simulated altitude of 3000 m. A similar relative exercise intensity corresponded to a lower absolute work load (139 +/- 4 W) in hypoxic than normoxic (163 +/- 4 W) conditions. Lower oxygen uptake (VO2) with no change in ventilation (VE), respiratory exchange ratio (R), and heart rate (Hr) were observed during exercise under hypoxia compared to normoxia. A slow rise in VO2, after the initial 5 min exercise, was observed in normoxic (+ 230 ml/min) as well as in hypoxic (250 ml/min) conditions that might be, in part, related to oxidative removal of blood lactate. Peak blood lactate concentration reached at 30 min of exercise was similar in normoxia (4.5 +/- 0.4) and in hypoxia (4.7 +/- 0.5). However, while the lactate level decreased during exercise at sea level, it remained elevated throughout exercise in altitude. Blood lactate concentration measured at the end of exercise was significantly (P less than 0.05) higher in hypoxic (4.4 +/- 0.3) than in normoxic (3.2 +/- 0.4) conditions. Catecholamine response to exercise was similar in both conditions. We conclude that during prolonged exercise at a given relative work load, hypoxia does not affect cardiorespiratory and sympathetic responses but tends to increase blood lactate accumulation. Higher blood lactate concentrations during hypoxic exercise seems to reflect alterations in the removal of blood lactate rather than changes in glycolytic flux.

[A comparison of cyclists' time records according to altitude and materials used]. / Comparaison du record de l'heure cycliste selon l'altitude et le matériel utilisé.

The purpose of this study was to re-assess the energy cost of track cycling in order (a) to compare the one-hour world records at sea-level and altitude with classical bicycles or with modern bicycles including aerodynamic components, and (b) to estimate the optimal altitude to set a new one-hour world record. Energy cost of track cycling with a classical or aerodynamic bicycle was estimated according to the equation developed by di Prampero et al. (1979) using data from Davies (1980) for the rolling resistance coefficient and from Gross et al. (1983) for the aerodynamic resistance coefficient for each type of bicycle. When compared to the classical track-bicycle, and to the bicycle studied by di Prampero et al. (1979), the aerodynamic track-bicycle reduces the resistance coefficient by 11.7 and 16.9% respectively. According to these estimations the cyclists sustain 87-95% of maximal aerobic power over one hour, which is a likely value for a 60 min exercise period for top-level athletes. When the reduction of air density and of maximal aerobic power with altitude are taken into account, equivalences between performances achieved at different altitudes and with the two types of track-bicycles, can be computed. The best overall performance appears to be the current one-hour record at sea-level using an aerodynamic bicycle (Moser: 50.644 km.h-1). This performance is equivalent to 53.5 km.h-1 in Mexico City (2230 m), 54.4 km.h-1 in La Paz (3417 m) and 54.5 km.h-1 at 3843 m (472 mmHg), which would be the optimal altitude to set the record.

[Value and duration of the bone localization of gallium in the mouse]. / Importance et durée de la localisation osseuse du gallium chez la souris

Gallium was administered subcutaneously to mice, and was found to be localized essentially in the skeleton. It was measured in the bones of animals given daily injections of gallium sulfate. There was little or no mortality. The amount of gallium found rose with the number of injections, and was greater when higher doses were injected. Elimination was very low after cessation of treatment. Results were used to study the action of gallium on cutaneous allografts in mice.

Plasma adrenocorticotrophin and cortisol responses to acute hypoxia at rest and during exercise.

Plasma adrenocorticotrophin (ACTH) and cortisol (F) concentrations were studied in six male subjects under normoxic (N) and acute hypoxic (H) conditions (altitude 3000 m) in a hypobaric chamber. Comparisons were made at rest, at 15, 30, and 60 min of exercise (65% VO2max), and after a 10 min recovery period. Mean (+/- SE) resting plasma ACTH levels were significantly higher in H (18.6 +/- 5.7 pmol.l-1) than in N (9.6 +/- 1.6 pmol.l-1) but no difference in resting plasma cortisol was observed between the two conditions. Both plasma ACTH and F concentrations were significantly increased at 60 min of exercise and during the recovery period under normoxic conditions. Hypoxia did not affect the ACTH response to exercise but reduced cortisol elevation. The changes in plasma cortisol concentration from rest to exercise were significantly correlated to ACTH under normoxic (r = 0.89, p less than 0.001) but not under hypoxic (r = 0.43, NS) conditions. Plasma lactate concentration was higher at the end of exercise in hypoxia (p less than 0.01), and no correlation existed between plasma lactate and ACTH levels. These observations provide further evidence that at sea level the increase in plasma cortisol levels during exercise is the result of ACTH-induced steroidogenesis. The responses observed at rest and during exercise in hypoxia suggest that adrenal sensitivity for ACTH may be altered.

Saliva flow and composition in humans exposed to acute altitude hypoxia.

The effects of acute hypoxia (2 days at 4350 m) on whole saliva flow and composition were studied on 12 sea-level natives, at rest and following a maximal exercise. Exercise, performed in normoxia and hypoxia, did not induce variations in saliva flow rate, saliva potassium or alpha-amylase concentrations. In contrast, acute hypoxia did lead to an increase in mean saliva flow rate both at rest (0.63 ml.min-1 to 0.93 ml.min-1, P less than 0.01) and after exercise (0.56 ml.min-1 to 1.06 ml.min-1, P less than 0.05) and a decrease in mean saliva potassium concentration at rest (20.8 mmol.l-1 to 14.7 mmol.l-1, P less than 0.01) as well as after exercise (21.7 mmol.l-1 to 16.5 mmol.l-1, P less than 0.05). This effect might be the consequence of a hypoxia-induced stimulation of the parasympathetic nervous system.

Metabolic and endocrine responses to graded exercise under acute hypoxia.

Eight male subjects (24 +/- 1 years old) performed graded ergocycle exercises in normoxic (N) and acute hypoxic (H) conditions (14.5% O2). VO2max decreased from 55.5 +/- 1.3 to 45.8 +/- 1.4 ml . kg-1 . min-1 in H condition. Plasma glucose and free fatty acid concentrations remained unchanged throughout exercise in both conditions. Increase in blood lactate concentration was associated with relative workload in both conditions. At VO2max lactate concentrations were similar in the two conditions, plasma insulin, glucagon, and LH concentrations did not significantly change in either. Plasma delta 4-androstenedione and testosterone increased in a similar manner in both conditions. Finally plasma norepinephrine concentration reached at VO2max was significantly lower in hypoxia. These results suggest that acute moderate hypoxia does not affect metabolic and hormonal responses to short exercise performed at similar relative workloads, i.e. when the reduction of VO2max due to hypoxia is taken into consideration. The lower catecholamine response to maximal exercise under acute hypoxia might suggest that the sympathetic response could be related to relative as well as absolute workloads.

Inhibition of exercise-induced blood prolactin response by acute hypoxia.

Prolactin (PRL) secretion is regulated by a variety of factors, most of them being known for their enhancing effects on blood PRL levels. This study describes the inhibitory influence of an acute exposure to hypoxia (14.5% O2) on the blood PRL response induced by graded maximal exercise in eight trained male subjects.