Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition

The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios −Δ[La] · ΔpH⁻¹ (where Δ[La] is change in lactic acid concentration and ΔpH is change in pH) and Δ[HCO₃ ⁻] · ΔpH⁻¹ (where Δ[HCO₃ ⁻] is change in bicarbonate concentration) in blood plasma. The difference between −Δ[La] · ΔpH⁻¹ and Δ[HCO₃ ⁻] · ΔpH⁻¹ yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, Δ[HCO₃ ⁻] · ΔpH⁻¹ can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7–8 days (group 1) or 11–12 days (group 2) after their return from a Himalayan expedition (2800–7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia −Δ[La] · ΔpH⁻¹ amounted to [mean (SEM)] 92 (6) mmol · l⁻¹ before altitude, of which 19 (4), 48 (1) and 25 (3) mmol · l⁻¹ were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude −Δ[La] · ΔpH⁻¹ was increased to 128 (12) mmol · l⁻¹ (P < 0.01) in group 1 and decreased to 72 (5) mmol · l⁻¹ in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol · l⁻¹ in group 1 and to 10 (2) mmol · l⁻¹ in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger [140 (18) mmol · l⁻¹]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here that the transport of La⁻ and H⁺ across cell membranes is differently influenced by high-altitude acclimatization. Accepted: 14 September 2000     

Effects of long-term acclimatization in lowlanders migrating to high altitude: comparison with high altitude residents

The physiological response to submaximal and maximal exercise was assessed in lowlanders and Tibetans at low (500 m above sea level) and high altitude (HA, 3 680 m). The times spent at HA by the lowland migrators was 8 days (n = 60), 7 months (n = 60, same group), 15 months (n = 29) and 27 months (n = 29). After the 15-month stay at HA, the maximal oxygen uptake ( O_2max) and maximal heart rate of the lowland migrators almost reached those of the HA native residents (Tibetans, n = 57), but their total work capacity and the gross efficiency () of mechanical work remained lower than those of the Tibetans. The rate of O_2max achieved at 90 W by the Tibetans was lower than that of the lowland migrators. It was concluded that, at HA, the lowlanders regained much of the aerobic capacity which they had lost initially. However, they did not attain the same gross mechanical efficiency as the Tibetans, who seemed to be at an advantage in respect of work at HA.     

Diurnal variations of serum erythropoietin in trained and untrained subjects

The diurnal variations of serum-erythropoietin concentration ([s-EPO]) were investigated in six physically trained (T) and eight untrained (UT) men. The T subjects had a higher mean maximal oxygen uptake than UT subjects [75.7 (SEM 1.6) ml · min^–1 · kg^–1 versus 48.3 (SEM 1.4) ml · min^–1 · kg^–1, P < 0.0001] and a lower mean body mass index [BMI, 21.7 (SEM 0.7) kg · m^–2 versus 24.4 (SEM 0.6) kg · m^–2, P=0.02]. Each subject was followed individually for 24 h as they performed their normal daily activities. Venous blood samples were collected from awakening (0 min) until the end of the 24-h period (1440 min). Both T and UT had a nadir of [s-EPO] 120 min after awakening [10.0 (SEM 0.3) U · 1^–1 versus 11.5 (SEM 2.1) U · 1^–1, P > 0.05]. The UT and T increased their [s-EPO] to peak values at 960 min and 960–1200 min, respectively (ANOVA P=0.03) after awakening [UT: 18.4 (SEM 2.8) U · l^–1; T: 16.2 (SEM 2.5) U · l^–1, P > 0.05]. The mean 24-h [s-EPO] were 14.5 (SEM 1.0) U · l^–1 and 14.9 (SEM 0.9) U · l^–1 in T and UT, respectively (P > 0.05). The individual mean 24-h [s-EPO] were not correlated to body mass, BMI or maximal oxygen uptaken. Significant diurnal variations in [s-EPO] occurred in these healthy subjects irrespective of their levels of physical activity.     

Effects and elimination of prednisolone in physically trained and untrained subjects

Summary After intravenous injection elimination and some effects of Prednisolone were compared in sportsmen and untrained individuals. The rate of elimination was higher in sportsmen possibly due to adaptive events during muscular training. The higher rate of elimination does not seem to reduce the steroid effects.     

Ventilatory and occlusion-pressure responses to exercise in trained and untrained children

Summary Pattern of breathing and mouth occlusion pressure were investigated during an incremental and exhaustive ergocycle test in untrained and trained 11 to 13 year old boys. At each level of exercise, the trained group had lower ventilation, a lower respiratory equivalent, and a lower respiratory rate. These results suggest that trained subjects have more efficient ventilation. Lower ventilation coincided with a smaller mean inspiratory flow (V_T/T_I), while the ratio of inspiratory to total breath (T_I/T_TOT) was unchanged. In contrast, mouth occlusion pressure and the index of neuromuscular inspiratory drive were the same up to 60 W for the two groups, and tended to be slightly lower in the trained boys above this level.     

Effect of food intake on exercise fatigue in trained and untrained subjects

Summary The effects of carbohydrate and fat intake on exercise-induced fatigue was investigated in 30 untrained — ( of 40.6±2.7 ml · kg⁻¹ · min⁻¹) and 24 trained-subjects ( of 52.3±2.7 ml · kg⁻¹ · min⁻¹) performing a 34 km march with a 25 kg backpack. Marching time was 8 1/2 h and 6 1/3 h in the untrained and trained-subjects respectively. The subjects were divided into 3 dietary groups. One group had free access to sugar cubes, the second group was offered almonds and the third one served as a control. Triglyceride levels decreased by 65 mg · dl⁻¹ in untrained, and by 115 mg · dl⁻¹ in trained subjects, while blood glucose remained at normal levels. In the untrained subjects, ingestion of almonds delayed the subjective sensation of exhaustion, while 50% of the controls and the sugar consuming subjects complained of exhaustion. The data suggest that ingestion of food containing fat delays exercise induced exhaustion or fatigue to a greater extent than does carbohydrate ingestion.     

Muscle triacylglycerol and hormone-sensitive lipase activity in untrained and trained human muscles

During exercise, triacylglycerol (TG) is recruited in skeletal muscles. We hypothesized that both muscle hormone-sensitive lipase (HSL) activity and TG recruitment would be higher in trained than in untrained subjects in response to prolonged exercise. Healthy male subjects (26 ± 1 years, body moss index 23.3 ± 0.5 kg m⁻²), either untrained (N = 8, VO_2max 3.8 ± 0.2 l min⁻¹) or trained (N = 8, VO_2max 5.1 ± 0.1 l min⁻¹), were studied. Before and after 3-h exercise (58 ± 1% VO_2max), a biopsy was taken. Muscle citrate synthase (32 ± 2 vs. 47 ± 6 μmol g⁻¹ min⁻¹ d.w.) and β-hydroxy-acyl-CoA-dehydrogenase (38 ± 3 vs. 52 ± 5 μmol g⁻¹ min⁻¹ d.w.) activities were lower in untrained than in trained subjects (p < 0.05). Throughout the exercise, fat oxidation was higher in trained than in untrained subjects (p < 0.05). Muscle HSL activity was similar at rest (0.72 ± 0.08 and 0.74 ± 0.03 mU mg⁻¹ protein) and after exercise (0.71 ± 0.1 and 0.68 ± 0.03 mU mg⁻¹ protein) in untrained and trained subjects. At rest, the chemically determined muscle TG content (37 ± 8 and 26 ± 5 mmol g⁻¹ d.w.) was similar (p > 0.05), and after exercise it was unchanged in untrained and lower (p < 0.05) in trained subjects (41 ± 9 and 10 ± 2 mmol g⁽¹ d.w.). Determined histochemically, TG was decreased (p < 0.05) after exercise in type I and II fibres. Depletion of TG was not different between fibre types in untrained, but tended to be higher (p = 0.07) in type I compared with type II fibres in trained muscles. In conclusion, HSL activity is similar in untrained and trained skeletal muscles both before and after prolonged exercise. However, the tendency to higher muscle TG recruitment during exercise in the trained subjects suggests a difference in the regulation of HSL or other lipases during exercise in trained compared with untrained subjects.     

Kinetics of plasma potassium concentrations during exhausting exercise in trained and untrained men

The purpose of this study was to examine the time course of changes in plasma potassium concentration during high intensity exercise and recovery in trained and untrained men. The subjects performed two exercise protocols, an incremental test and a sprint, on a cycle ergometer. A polyethylene catheter was inserted into the antecubital vein to obtain blood samples for the analysis of plasma electrolyte concentrations and acid-base parameters, during and after exercise. During both tests, venous plasma sodium, potassium and chloride concentrations increased in all the subjects, although the largest relative increase was detected in potassium concentration - 35% and 31% over rest in the progressive test and 61% and 37.7% in the sprint test, for cyclists and controls, respectively. After exercise plasma potassium concentration decreased exponentially to below resting values. There was a linear correlation between the amount of potassium accumulated in plasma during exercise and the amount eliminated from plasma when the exercise ceased. We found that, although plasma potassium accumulation occurred in both forms of exercise in the trained and nontrained subjects, the time constant of potassium decrease following exercise was shorter in the trained subjects. Thus, the trained subjects exhibited a better capacity to recover to resting concentrations of plasma potassium. We propose that the extracellular potassium accumulation acts as a negative feedback signal for sarcolemma excitability depending on the muscle metabolic rate.     

The effects of high-intensity exercise on skeletal muscle neutrophil myeloperoxidase in untrained and trained rats

The primary purpose of this study was to examine the effects of high-intensity acute exercise on neutrophil infiltration in different muscle fiber types of untrained rats and to compare postexercise neutrophil accumulation in muscles of untrained and trained animals. The effect of high-intensity acute exercise on blood neutrophil degranulation reaction in trained animals was also elucidated. Neutrophil enzyme myeloperoxidase (MPO) was determined as a measure of neutrophil migration into muscles and blood neutrophil degranulation. Male albino rats were subjected to acute exercise and 5 weeks of training. The used model of intensive acute exercise consisted of 5, 15, and 25 intermittent swimming bouts with the addition of weight (8% of total body mass) for 1-min each, followed by 1.5-min rest intervals. MPO was analyzed in quadriceps muscle (white and red portion) and in soleus muscle 24 h after acute exercise. MPO content in resting blood plasma and neutrophils was determined 48-h following the completion of a training process. In addition, MPO content in the trained rats was measured immediately (in blood plasma and neutrophils) after and 24 h (in muscles) following a single-bout of exercise to exhaustion. The remaining two-third of the trained animals were exposed to a single-bout of nonstop swimming with the addition of 6% body mass until exhaustion. These animals were sacrificed immediately and 24 h after loaded swimming to analyze leukocyte count, MPO content in blood plasma and neutrophils and in muscles, respectively. About 24 h after exercise MPO concentrations in the red portion of quadriceps muscle and in soleus muscle were 4–7-fold higher as compared to the white portion of m. quadriceps. There was an association between the quantity of repetitive bouts of swimming and MPO content in the muscles. The duration of swimming to exhaustion of trained rats was 3.8-fold longer than untrained sedentary control. At rest, plasma MPO concentration was found to be 40% higher in trained rats compared to untrained controls (P < 0.05). Postexercise plasma MPO concentrations were significantly higher both in untrained (+137%; P < 0.05) and trained (+81%; P < 0.05) rats compared to resting values. At rest neutrophil MPO concentration was found to be 33% lower in trained rats compared to untrained controls (P < 0.05). There were no significant differences in muscle MPO concentrations between untrained and trained rats at rest. A single-bout of exercise to exhaustion produced a greater increase in MPO content in untrained compared to trained rats. The data suggest that postexercise neutrophil infiltration is more intensive in red fibers types compared to white fiber types. A smaller neutrophil infiltration in muscles of trained animals after exhaustive exercise suggests a protective effect of previous training to muscle injury.Portions of this paper were presented by V. Morozov in 2003 at the 6th ISEI Symposium on Exercise Muscle Metabolism and Immune Function, Copenhagen.     

Respiratory and cardiac responses to exercise-simulating peripheral perfusion in endurance trained and untrained rats

Summary In endurance trained (TR) and untrained (UTR) rats heart rate (HR) and respiratory rate (RR) were recorded during perfusion of the circulatorily isolated hind leg of the rat with exercise simulating modified tyrode solutions (TR: n=10, UTR: n=10; compare part I). During the 20 min test period and the preceding and succeeding periods of control perfusions with an unmodified tyrode solution, [lactate], pH, [K⁺], [Na⁺], PO₂ and PCO₂ were measured in the outflow of the femoral vein. In 3 experimental series: (1) hypoxic tyrode solution enriched with lactic acid (15 mmol·l^–1), (2) normoxic solution with lactic acid, (3) hypoxic solution without lactic acid, were applied. The outflow parameters were cross correlated with both HR and RR. The analysis revealed a significant temporal relationship between [lactate], pH, PO₂, PCO₂ and [K⁺] and both HR and RR. In the trained rats no temporal correlation between either of the outflow and reflex parameters could be determined. This result was not due to low [lactate], but was also found during perfusion with lactic acid. In all 3 test conditions [lactate] in untrained individuals was best correlated with both HR and RR. Although the correlation peaks of the respiratory response, but not of the HR response were definitely lower in normoxic lactic and perfusion than in the two other experimental conditions, both inter- and intraindividual correlation analyses revealed a high degree of interdependence between respiratory and cardiac responses.Dedicated to J. Stegemann on the occasion of his 60th anniversaryThis work was supported by grants (No. 06/06040/68511) from the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen and the Görres Gesellschaft zur Pflege der WissenschaftPreliminary reports of this work was presented at the spring meetings of the Deutsche Physiologische Gesellschaft, March 1986, in Berlin and March 1987, in Homburg     

The relationship of plasma ammonia and lactate concentrations to perceived exertion in trained and untrained women

Summary The purpose of this study was to investigate the covariance between perceived exertion (recorded using Borg's category-ratio scale CR-10) and the relative oxygen uptake, and lactate and ammonia concentrations in blood from a peripheral vein. Ratings of perceived exertion (RPE) at 25%, 50%, 75% and 90% maximal oxygen uptake and lactate and ammonia concentrations were compared in well-trained women distance runners (n = 22) and untrained women (n = 10). Ammonia concentrations in peripheral venous blood were significantly correlated with RPE (P < 0.05), both in the trained and untrained women. Differences between the trained and untrained subjects occurred when the ammonia concentration increased to 148 mol · l^–1 in both groups investigated; similarly, the mean RPE correlated significantly with the lactate concentration (P < 0.05), both in the trained and untrained women and there was a difference in RPE between groups when lactate concentration in the blood had risen to 4.4 mmol · l^–1. It would seem that the correlation of blood ammonia and lactate concentrations with RPE during exercise could be a useful indicator of the development of fatigue.     

Extracellular bicarbonate and non-bicarbonate buffering against lactic acid during and after exercise

Defense of extracellular pH constancy against lactic acidosis can be estimated from changes (Δ) in lactic acid ([La]), [HCO₃⁻], pH and PCO₂ in blood plasma because it is equilibrated with the interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 13 untrained (UT) and 21 endurance-trained (TR) males to find out if acute and chronic exercise influence the defense. During exercise the capacity of non-bicarbonate buffers (β_nbi = −Δ[La] · ΔpH⁻¹ − Δ[HCO₃⁻] · ΔpH⁻¹) available for the extracellular fluid (mainly hemoglobin, dissolved proteins and phosphates) amounted to 32 ± 2(SEM) and 20 ± 2 mmol l⁻¹ in UT and TR, respectively (P < 0.02). During recovery β_nbi decreased to 14 (UT) and 12 (TR) mmol l⁻¹ (both P < 0.001) corresponding to values previously found at rest by in vivo CO₂ titration. Bicarbonate buffering (β_bi) amounted to 44–48 mmol l⁻¹ during and after exercise. The large exercise β_nbi seems to be mainly caused by an increasing concentration of all buffers due to shrinking of the extracellular volume, exchange of small amounts of HCO₃⁻ or H⁺ with cells and delayed HCO₃⁻ equilibration between plasma and interstitial fluid. Increase of [HCO₃⁻] during titration by these mechanisms augments total β and thus the calculated β_nbi more than β_bi because it reduces ΔpH and Δ[HCO₃⁻] at constant Δ[La]. The smaller rise in exercise β_nbi in TR than UT may be caused by an increased extracellular volume and an improved exchange of La⁻, HCO₃⁻ and H⁺ between trained muscles and blood.     

Effects of exercise intensity and duration on fat metabolism in trained and untrained older males

Advancing age is associated with changes in fat and carbohydrate (CHO) metabolism, which is considered a risk factor for cardiovascular disease and diabetes. The effects of exercise intensity and duration on fat and CHO metabolism in elderly male subjects were investigated in the present study. Seven trained (63.7 ± 4.7 years) and six untrained (63.5 ± 4.5 years) healthy males performed three 30 min trials on a cycle ergometer at 50, 60 and 70% and two other trials at 60 and 70% in which the total energy expenditure was equal to that for 30 min at 50% Respiratory measures were undertaken throughout the exercise and blood samples taken before and immediately after each trial. Statistical analyses revealed a significant effect of exercise intensity on fat oxidation when the exercise durations were equated as well as when the energy expenditure was held constant for the three trials, though no training effect was noted. Total carbohydrate oxidation increased significantly with exercise intensity (P < 0.05) and with training. Significantly higher levels of non-esterified free fatty acid (NEFA) and glycerol were observed for trained compared with untrained though not for B-hydroxybutyrate (3-OH) or insulin. No differences in NEFA, glycerol, 3-OH were evident for increases in exercise intensity. Carbohydrate and fat oxidation are significantly affected by exercise intensity in elderly males, although only CHO oxidation is influenced by training. Furthermore, training-induced increases in the availability of NEFA and glycerol are not associated with an increase in fat oxidation, rather an increase in CHO oxidation.     

Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise

Summary The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15–16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption ( O_2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (P _{I max}) and expiratory (P _{E max}) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (V _T), respiratory frequency (f _R), ventilation] and the relative contribution of ribcage and abdomen to V _T were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMG_tr) and diaphragm (EMG_di) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; f _R increased significantly (P < 0.05) at 40% O_2maxfor the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% O_2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: P _{I max}, P _{E max} and the frequency spectrum of EMG_tr and EMG_di were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that P _{I max} was significantly decreased after exercise.     

Effect of bovine colostrum supplementation on the composition of resistance trained and untrained limbs in healthy young men

This study examined the effect of bovine colostrum (BC) supplementation on the tissue composition of resistance trained (T) and untrained (UT) limbs. Using a double-blind design, subjects were randomly allocated to 60 g day^–1 of BC (n=17) or whey protein (WP) (n=17) during 8 weeks of resistance training of the elbow flexors (EF) of their non-dominant arm (T). Axial magnetic resonance images of both upper arms, maximal voluntary isometric torque (MVC) of EF, and the one repetition maximum (1RM) for bicep curls were measured pre- and post-supplementation. There were no differences in macronutrient intakes (P>0.28) or the volume of training completed by T (P=0.98) between the two groups. T of BC experienced a significantly greater increase in circumference [BC 2.3 (3.0)%, WP 0.0 (4.2)%; P=0.05] and cross-sectional area (CSA) [BC 4.2 (6.0)%, WP –0.2 (8.3)%; P=0.05] compared with WP, due principally to a greater increase in skin and subcutaneous fat (SSF) CSA [BC 5.5 (10.9)%, WP –2.7 (14.1)%; P=0.03]. No tissue compartment changed significantly in UT of either group (P>0.05). MVC and 1RM increased for T and UT in both groups (P<0.05), but the increases were not different between groups (P>0.32). Since the SSF compartment increased in T but not UT, and fat turnover in adipocytes is under hormonal control and would not be localised to one arm, we suggest that the increase in SSF CSA in T of BC may have been due to an increase in skin CSA, rather than fat.     

Respiratory compensation and blood pH regulation during variable intensity exercise in trained versus untrained subjects

To determine whether endurance-trained cyclists (T; n = 10) have a superior blood-respiratory buffering for metabolic acidosis relative to untrained subjects (UT; n = 10) during variable intensity exercise (VAR). On three occasions, T and UT pedaled for 24 min alternating high- and low-intensities as percentage of their second ventilatory threshold (VT₂): VAR_LOW 87.5–37.5% VT₂, VAR_MODERATE 125–25% VT₂, and VAR_HIGH 162.5–12.5% VT₂ to complete the same amount of work. Before and just after each VAR trial, maximal cycling power (P_MAX) was assessed. For each trial, the respiratory compensation for exercise acidosis (ventilatory equivalent for CO₂) and the final blood pH, lactate and bicarbonate concentrations were similar for T and UT subjects. However, after VAR_HIGH, UT reduced P_MAX (−14 ± 1%; P < 0.05) while T did not. Our data suggest that endurance training confers adaptations to withstand the low pH provoked by VAR without losing cycling power, although this response is not due to differences in blood-respiratory buffering.     

Oxygen dissociation curves in trained and untrained subjects

Summary Oxygen dissociation curves (ODC) in whole blood and organic phosphate concentrations in red cells were determined in 10 highly trained male athletes (TR), 6 semitrained subjects (ST) who played sports regularly at low intensities and 8 untrained people (UT). In all groups standard ODCs (37 C, pH 7.40, Pco₂43 Torr) at rest and after a short exhaustive exercise were nearly identical, but P _o2 values measured immediately after blood sampling and corrected to standard conditions tended to fall to the right of the in vitro ODC. Elevated P₅₀ in the physically active [28.6±1.4 Torr (3.81±0.18 kPa) in ST, 28.0±1.1 Torr (3.73±0.15 kPa) in TR, but 26.5±1.1 Torr (3.53±0.15 kPa) in UT] were partly caused by different [DPG] (11.9±1.3 mol/gHb in UT, 13.3±1.5 mol/gHb in TR, 13.8±2.2 mol/gHb in ST). There were remarkable differences in the shape of the curves between the groups. The slope n in the Hill plot amounted to 2.65±0.12 in UT, 2.74±0.12 in ST and 2.90±0.11 in the TR (2 p against UT<0.001), leading to an elevated oxygen pressure of about 2 Torr (0.27 kPa) at 20% saturation and an augmented oxygen extraction of 5–7 So₂ at a Po₂ of about 15 Torr (2 kPa), which might be favorable at high workloads.The reason for the phenomenon could be an increased amount of young red cells in the blood of TR, caused by exercise induced hemolysis.A preliminary report was presented at the 49th Meeting of the German Physiological Society [Pflügers Arch. (Suppl.), 373, R 57 (1978)]     

Plasma AVP,neurophysin, renin activity,and aldosterone during submaximal exercise performed until exhaustion in trained and untrained men

Summary The effect of intense muscular work (80% of maximal oxygen uptake) on responses of plasma hormones involved in electrolyte and water balance were measured in 14 male subjects. They were divided into three groups according to their maximal oxygen uptake and the duration of exercise performed until exhaustion: well trained subjects (group I), trained subjects (group II), and untrained subjects (group III).Pulmonary gas exchange, heart rate, rectal and skin temperature, and weight loss were measured as well as hematocrit and plasma and urine sodium and potassium concentrations.Rectal temperature increased significantly in all subjects after exhaustion. The variation of hematocrit was smallest and the weight loss greatest in the well-trained subjects. Plasma aldosterone, renin activity (PRA), vasopressin (AVP), and neurophysin (Np) displayed highly significant increases after exercise in all three groups: PRA was increased 4.5 times (p<0.01), aldosterone 13 times (p<0.05), Np 2.6 times (p<0.05), and AVP 4.8 times (p<0.05). Nevertheless, there was no correlation between the changes in PRA and those in plasma aldosterone, nor between aldosterone and plasma sodium or potassium.At the urinary level, the only striking observation was that free water clearance tends to become positive after exercise. Our results provide evidence that this kind of exercise produces a highly significant increase in plasma levels of the hormones involved in electrolyte and water balance. They also indicate that it is among the well-trained subjects that sweat loss is highest though the hematocrit increase is the smallest; this suggests that water is shifted more efficiently from the extravascular compartment.     

Cardiovascular response to static handgrip in trained and untrained men

Summary The influence of aerobic capacity on the cardiovascular response to handgrip exercise, in relation to the muscle mass involved in the effort, was tested in 8 trained men (T) and 17 untrained men (U). The subjects performed handgrip exercises with the right-hand (RH), left-hand (LH) and both hands simultaneously (RLH) at an intensity of 25% of maximal voluntary contraction force. Maximal aerobic capacity was 4.3 l·min^–1 in T and 3.21·min^–1 in U (P<0.01). The endurance time for handgrip was longer in T than in U by 29% (P<0.05) for RH, 38% (P<0.001) for LH and 24% (P<0.001) for RLH. Heart rate (f _c) was significantly lower in T than in U before handgrip exercise, and showed smaller increases (P<0.01) at the point of exhaustion: 89 vs 106 beats·min^–1 for RH, 93 vs 100 beats·min^–1 for LH and 92 vs 108 beats·min^–1 for RLH. Stroke volume (SV) at rest was greater in T than in U and decreased significantly (P<0.05) during handgrip exercise in both groups of subjects. At the point of exhaustion SV was still greater in T than in U: 75 vs 57 ml for RH, 76 vs 54 ml for LH and 76 vs 56 ml for RLH. During the last seconds of handgrip exercise, the left ventricular ejection time was longer in T than in U. Increases in cardiac output (Q _c) and systolic blood pressure did not differ substantially between T and U, nor between the handgrip exercise tests. It was concluded that handgrip exercise caused similar increases inQ _c in both T and U but in T the increased level ofQ _c was an effect of greater SV and lowerf _c than in U. Doubling the muscle mass did not alter the cardiovascular response to handgrip exercise in either T or U.     

Maximal fat oxidation rates in endurance trained and untrained women

The aim of the present study was to examine the differences in fat oxidation between endurance trained (ET) and untrained (UT) women. Eight ET and nine UT women performed a progressive cycle ergometer test until exhaustion. The rate of fat oxidation was similar at low work rates (≤90 W) but was 80–200% higher in ET subjects at 120–180 W. When related to relative exercise intensity, the fat oxidation was similar in the low-intensity domain (≤40% VO₂max), but higher in the ET subjects both at moderate intensities (45–60% VO₂max; +22% vs. UT) and at high intensities (65–80% VO₂max; +35% vs. UT). There was no difference in the maximal fat oxidation rates between the trained and untrained women. The relative exercise intensity that elicited the highest rate of fat oxidation (Fat_max) was 56 ± 3% and 53 ± 2% VO₂max in ET and UT women, respectively (NS). In biopsies from m. vastus lateralis, the activity of the enzymes citrate synthase, β-hydroxy acyl CoA dehydrogenase (HAD), and hormone sensitive lipase was higher in the ET subjects. The HAD activity correlated significantly with fat oxidation at moderate and high intensities. We conclude that the ET women had a higher fat oxidation at moderate- and high-exercise intensities both at same relative and at absolute intensity compared with the UT women. The HAD activity and fat oxidation rates were highly correlated indicating that training-induced adaptation in muscle fat oxidative capacity is an important factor for enhanced fat oxidation. Interestingly, maximal fat oxidation occurred at the same exercise intensity.