Plasma volume, osmolarity, total protein and electrolytes during treadmill running and cycle ergometer exercise

Impact of a single blood donation on hemoglobin mass, iron stores, and maximum oxygen uptake in pre-menopausal women-A pilot study

BACKGROUND

During whole blood donation (BD), 500 mL of blood is drawn. The time interval between two BDs is at least 8-12 weeks. This period might be insufficient for restoring hemoglobin mass (Hbmass) and iron especially in women, who generally have lower Hbmass and iron availability. Since both variables influence physical performance, this pilot study aimed to monitor Hbmass, iron status, and maximum oxygen uptake (V̇O2max) recovery in women after a single BD.

STUDY DESIGN AND METHODS

In 10 women (24.7 ± 1.7 years), Hbmass, hemoglobin concentration [Hb], iron status, and V̇O2max were assessed before and up to 12 weeks after a single BD.

RESULTS

BD reduced Hbmass from 562 ± 70 g to 499 ± 64 g (p < .001). Although after 8 weeks no significant mean difference was detected, 7 women had not returned to baseline after 12 weeks. [Hb] did not return to initial values (13.4 ± 0.7 g/dL) after 12 weeks (12.9 ± 0.7 g/dL, p < .01). Ferritin decreased from baseline until week 6 (40.9 ± 34.2 ng/mL vs. 12.1 ± 6.9 ng/mL, p < .05) and was not restored after 12 weeks (18.4 ± 12.7 ng/mL, p < .05), with 6 out of 10 women exhibiting iron deficiency (ferritin <15 ng/mL). V̇O2max was reduced by 213 ± 47 mL/min (7.2 ± 1.2%; p < .001) and remained below baseline after 12 weeks (3.2 ± 1.4%, p < .01).

DISCUSSION

For most pre-menopausal women, 12 weeks were not sufficient to recover from BD and achieve baseline Hbmass and iron stores resulting in prolonged reduction of aerobic capacity. A subsequent BD might lead to a severe anemia.

Improvements in Maximal Oxygen Uptake After Sprint-Interval Training Coincide with Increases in Central Hemodynamic Factors

INTRODUCTION

Sprint-interval training has been shown to improve maximal oxygen uptake, in part through peripheral muscle adaptations that increase oxygen utilization. In contrast, the adaptations of central hemodynamic factors in this context remain unexplored.

PURPOSE

The aim of the current study was to explore the effects of sprint-interval training on maximal oxygen uptake and central hemodynamic factors.

METHODS

Healthy men and women (n = 29; mean age, 27 ± 5 yr; height, 175 ± 8 cm; body mass, 72.5 ± 12.0 kg) performed 6 wk of sprint-interval training consisting of three weekly sessions of 10-min low-intensity cycling interspersed with 3 × 30-s all-out sprints. Maximal oxygen uptake, total blood volume, and maximal cardiac output were measured before and after the intervention.

RESULTS

Maximal oxygen uptake increased by 10.3% (P < 0.001). Simultaneously, plasma volume, blood volume, total hemoglobin mass, and cardiac output increased by 8.1% (276 ± 234 mL; P < 0.001), 6.8% (382 ± 325 mL; P < 0.001), 5.7% (42 ± 41 g; P < 0.001), and 8.5% (1.0 ± 0.9 L·min-1; P < 0.001), respectively. Increased total hemoglobin mass along with measures of body surface area had a significant impact on the improvements in maximal oxygen uptake.

CONCLUSIONS

Six weeks of sprint-interval training results in significant increases in hemoglobin mass, blood volume, and cardiac output. Because these changes were associated with marked improvements in maximal oxygen uptake, we conclude that central hemodynamic adaptations contribute to the improvement in maximal oxygen uptake during sprint-interval training.

Dehydrated males are less likely to dive into the mating pool

The hydration state of animals vying for reproductive success may have implications for the tempo and mode of sexual selection, which may be salient in populations that experience increasing environmental fluctuations in water availability. Using red-sided garter snakes as a model system, we tested the effect of water supplementation on courtship, mating behavior, and copulatory plug (CP) production during a drought year. Over 3 days of mating trials, water-supplemented males (WET males, n = 45) outperformed a control group that was not supplemented with water (DRY males, n = 45). Over 70% of WET males mated but just 33% of DRY males did so. As a group, WET males mated 79 times versus 28 times by DRY males. On the last day of mating trials, over 70% of WET males were still courting, with 19 of them mating, whereas less than 25% of DRY males were courting and only one mated. CP deposition accounted for 4–6% of the mass lost by mating males, but hydration did not affect CP mass or water content. These findings suggest that, in years of low water availability, the number of courting males and the intensity of their courtship declines, thereby affecting sexual selection and conflict, at least within that year.

Interval-induced metabolic perturbation determines tissue fluid shifts into skeletal muscle

Intense interval exercise has proven to be as effective as traditional endurance exercise in improving maximal oxygen uptake. Shared by these two exercise regimes is an acute reduction in plasma volume, which is a suggested stimulus behind exercise-induced increases in blood volume and maximal oxygen uptake. This study aimed to link exercise-induced metabolic perturbation with volume shifts into skeletal muscle tissue. Ten healthy subjects (mean age 33 ± 8 years, 5 males and 5 females) performed three 30 s all-out sprints on a cycle ergometer. Upon cessation of exercise magnetic resonance imaging, ³¹ Phosphorus magnetic resonance spectroscopy and blood samples were used to measure changes in muscle volume, intramuscular energy metabolites and plasma volume. Compared to pre-exercise, muscle volume increased from 1147.1 ± 35.6 ml to 1283.3 ± 11.0 ml 8 min post-exercise. At 30 min post-exercise, muscle volume was still higher than pre-exercise (1147.1 ± 35.6 vs. 1222.2 ± 6.8 ml). Plasma volume decreased by 16 ± 3% immediately post-exercise and recovered back to - 5 ± 6% after 30 min. Principal component analysis of exercise performance, muscle and plasma volume changes as well as changes in intramuscular energy metabolites showed generally strong correlations between metabolic and physiological variables. The strongest predictor for the volume shifts of muscle and plasma was the magnitude of glucose-6-phosphate accumulation post-exercise. Interval training leads to large metabolic and hemodynamic perturbations with accumulation of glucose-6-phosphate as a possible key event in the fluid flux between the vascular compartment and muscle tissue.

Comparison of haemoglobin assessments by HemoCue and two automated haematology analysers in young Laotian children

Background

Haemoglobin (Hb) assessment by Hemocue is used widely for anaemia screening in both adults and children. However, few studies have compared the diagnostic accuracy of Hemocue with an automated haematology analyser in young children.

Aim

To compare Hb concentrations by Hemocue Hb301 and two automated haematology analysers in young children in rural communities of Lao PDR.

Methods

Capillary blood was collected from 6-month-old to 23-month-old children (n=1487) for determination of Hb concentration by Hemocue Hb301. On the same day, venous blood was collected for complete blood count using one of two haematology analysers (XT-1800i, Sysmex, and BC-3000Plus, Mindray Medical International). In a subsample of children (n=129), venous Hb was also measured by HemoCue Hb301. Agreement between the two methods was estimated using Bland-Altman plots.

Results

Mean capillary Hb by Hemocue was significantly higher than mean venous Hb by haematology analysers combined (108.4±10.3 g/L vs 102.3±13.1 g/L; P<0.001), resulting in a significantly lower anaemia prevalence (Hb <110 g/L) by Hemocue (53.7% vs 73.9%; P<0.001). The Bland-Altman assessment of agreement showed a bias of 6.1 g/L and limits of agreement were −11.5 g/L to 23.7 g/L. Mean venous Hb concentration by Hemocue Hb301 (113.6±14.0 g/L) was significantly higher than mean capillary Hb concentration by Hemocue Hb301 (110.0±10.7; P=0.03 g/L), which in turn was significantly higher than mean venous Hb concentration by the Mindray BC-3000Plus (102.3±17.4 g/L).

Conclusion

Capillary and venous Hb concentrations assessed by Hemocue Hb301 showed poor agreement compared with venous Hb by automated haematology analysers, resulting in significantly different anaemia prevalences.

Non-linear actions of physiological agents: Finite disarrangements elicit fitness benefits

Finite disarrangements of important (vital) physiological agents and nutrients can induce plethora of beneficial effects, exceeding mere attenuation of the specific stress. Such response to disrupted homeostasis appears to be universally conserved among species. The underlying mechanism of improved fitness and longevity, when physiological agents act outside their normal range is similar to hormesis, a phenomenon whereby toxins elicit beneficial effects at low doses. Due to similarity with such non-linear response to toxins described with J-shaped curve, we have coined a new term “mirror J-shaped curves” for non-linear response to finite disarrangement of physiological agents. Examples from the clinical trials and basic research are provided, along with the unifying mechanisms that tie classical non-linear response to toxins with the non-linear response to physiological agents (glucose, oxygen, osmolarity, thermal energy, calcium, body mass, calorie intake and exercise). Reactive oxygen species and cytosolic calcium seem to be common triggers of signaling pathways that result in these beneficial effects. Awareness of such phenomena and exploring underlying mechanisms can help physicians in their everyday practice. It can also benefit researchers when designing studies and interpreting growing number of scientific data showing non-linear responses to physiological agents.

Monitoring recovery from iron deficiency using total hemoglobin mass

INTRODUCTION

Using hemoglobin concentration ([Hb]) to diagnose borderline iron deficiency and monitor the progress of its treatment is difficult because of the confounding effects of plasma volume. Because hemoglobin mass (Hbmass) is not affected by plasma volume, it may be a more sensitive parameter. The aim of this study was to monitor Hbmass, iron storage, and maximal oxygen consumption (V˙O2max) during and after oral iron therapy in subjects with severe and moderate iron deficiency.

METHODS

Three groups of female recreational athletes were monitored for at least 22 wk, as follows: 1) severe iron deficiency group (SID) (n = 8; ferritin, ≤12 ng·mL), 2) moderate iron deficiency group (MID) (n = 14; ferritin, ≤25 ng·mL), and 3) control group (n = 8; ferritin, >25 ng·mL). Hbmass and iron status were determined before, during, and up to 12 wk after at least 10 wk of oral iron supplementation. In total, five V˙O2max tests were performed before, during, and after the supplementation period.

RESULTS

Hbmass increased markedly in the SID group (15.6% ± 11.0%, P < 0.001) and slightly in the MID group (2.2% ± 3.7%, P < 0.05) by the end of the supplementation period and remained at this level for the following 12 wk. [Hb] and Hbmass were similarly affected, but Hbmass was more closely related to mean corpuscular volume and mean corpuscular hemoglobin than [Hb]. The SID group incorporated 534 ± 127 mg of iron into ferritin and hemoglobin, whereas the MID group incorporated 282 ± 68 mg of iron. V˙O2max increased only in the SID group by 0.20 ± 0.18 L·min (P < 0.05) and was closely related to Hbmass (P < 0.01).

CONCLUSIONS

Hbmass is a sensitive tool for monitoring recovery from iron deficiency anemia and assessing the effectiveness of iron supplementation in individuals with severe or moderate iron deficiency.

Carbohydrate electrolyte solutions enhance endurance capacity in active females

The purpose of the present study was to investigate the effects of supplementation with a carbohydrate-electrolyte solution (CES) in active females during a prolonged session of submaximal running to exhaustion. Eight healthy active females volunteered to perform a session of open-ended running to exhaustion at 70% of their maximal oxygen consumption on a treadmill during the follicular phase of their menstrual cycle on two occasions. During each run, the subjects consumed either 3mL·kg⁻¹ body mass of a 6% CES or a placebo drink (PL) every 20 min during exercise. The trials were administered in a randomized double-blind, cross-over design. During the run, the subjects ingested similar volumes of fluid in two trials (CES: 644 ± 75 mL vs. PL: 593 ± 66 mL, p > 0.05). The time to exhaustion was 16% longer during the CES trial (106.2 ± 9.4 min) than during the PL trial (91.6 ± 5.9 min) (p < 0.05). At 45 min during exercise, the plasma glucose concentration in the CES trial was higher than that in PL trial. No differences were observed in the plasma lactate level, respiratory exchange ratio, heart rate, perceived rate of exertion, sensation of thirst, or abdominal discomfort between the two trials (p > 0.05). The results of the present study confirm that CES supplementation improves the moderate intensity endurance capacity of active females during the follicular phases of the menstrual cycle. However, the exogenous oxidation of carbohydrate does not seem to explain the improved capacity after CES supplementation.

Evaluation of two methods to measure hemoglobin concentration among women with genetic hemoglobin disorders in Cambodia: a method-comparison study

BACKGROUND

Genetic hemoglobin (Hb) E variants are common in Cambodia and result in an altered and unstable Hb molecule. We evaluated two methods to measure Hb concentration among individuals with and without Hb variants using a hemoglobinometer (HemoCue) and a hematology analyzer (Sysmex XT-1800i).

METHODS

We determined the bias and concordance between the methods among 420 Cambodian women (18-45 y).

RESULTS

Bias and concordance appeared similar between methods among women with no Hb disorders (n=195, bias=2.5, ρc=0.68), women with Hb E variants (n=133, bias=2.5, ρc=0.78), and women with other Hb variants (n=92, bias=2.7, ρc=0.73). The overall bias was 2.6g/l, resulting in a difference in anemia prevalence of 11.5% (41% using HemoCue and 29.5% using Sysmex, p<0.001). Based on visual interpretation of the concordance plots, the HemoCue device appears to underestimate Hb concentrations at lower Hb concentrations and to overestimate Hb concentrations at higher Hb concentrations (in comparison to the Sysmex analyzer).

CONCLUSIONS

Bias and concordance were similar across groups, suggesting the two methods of Hb measurement were comparable. We caution field staff, researchers and policy makers in the interpretation of data and the impact that bias between methods can have on anemia prevalence rates.

Separate and combined influence of posture and sprint running on plasma volume changes

It is currently unknown whether any changes in plasma volume (PV) after sprint running are inherent to sprint running per se or are due to other confounding factors such as changes in posture. The purpose of the present study was to examine the independent effects of sprint running on PV changes. Eight females completed two trials on separate days: (1) a 30-s sprint on a non-motorised treadmill and (2) a control trial where no exercise was undertaken but blood samples were taken at identical time points as in the exercise trial. Changes in PV were calculated using haematocrit and haemoglobin. Post-sprint PV reductions were greater in the sprint than the control trial (mean: -17.7, SD=3.1% vs. mean: -7.5, s = 4.9, P<0.05, n=8). There were greater changes in PV in the sprint than the control trial in most sampling points. These data show that sprint running of only 30 s induces transient reductions in PV independently of posture change. The present findings suggest that PV changes due to sprint running should be routinely reported as well as the posture and the exact time in this posture.

Exercise-induced hypoxemia: fact or fallacy?

Whereas the prevalence of exercise-induced hypoxemia (EIH) in endurance athletes is commonly reported as approximately 50%, most previous studies have not corrected PaO2 for exercise-induced hyperthermia. Furthermore, although a detrimental effect on aerobic performance has been assumed, no study has measured arterial oxygen content (CaO2) in this context.

PURPOSE

To determine the effect of temperature-correcting PaO2 values for rectal, arterial blood, esophageal, and exercising muscle temperatures during exercise on CaO2 and the prevalence of EIH.

METHODS

Twenty-three trained males (age 26 +/- 5 yr; VO2peak 65.2 +/- 1.6 mL x kg-1 x min-1) performed incremental treadmill exercise to exhaustion with PaO2 corrected for simultaneous temperature measurements at all four sites. EIH was defined as DeltaPaO2 >or= 10 mm Hg.

RESULTS

: With no temperature correction, DeltaPaO2 was -20.8 +/- 5.0 mm Hg and prevalence was 96% (n = 23), but when corrected for rectal temperature, DeltaPaO2 was -14.7 +/- 7.8 mm Hg and prevalence was 73% (n = 20); for arterial blood temperature, DeltaPaO2 was -7.7 +/- 6.5 mm Hg and prevalence was 35% (n = 20); and for esophageal temperature, DeltaPaO2 was -8.1 +/- 7.7 mm Hg and prevalence was 48% (n = 23), although when corrected for active muscle temperature, DeltaPaO2 was +8.2 +/- 7.8 mm Hg and prevalence was 0% (n = 10). There were no significant changes in CaO2 except for uncorrected values, and there was no correlation between DeltaPaO2 and VO2peak.

CONCLUSIONS

Although the prevalence of EIH depends on the temperature correction applied to PaO2 values, in no case is there a significant change in CaO2 or any relationship with maximal aerobic power.

Effects of glycemic index meal and CHO-electrolyte drink on cytokine response and run performance in endurance athletes

OBJECTIVE

To examine the effect of the glycemic index (GI) of a pre-exercise (PRE-ex) meal on plasma cytokine responses and endurance performance when carbohydrate-electrolyte (CHO-E) drink was consumed during exercise.

METHODS

Eight endurance-trained male runners (age: 28.6+/-2.7 years; body mass: 61.9+/-1.71 kg; V O(2max): 58.5+/-1.6 ml kg(-1)min(-1)) completed three trials in a randomized order. The pre-exercise meal consisted of either high-GI (HGI) (GI=83), low-GI (LGI) foods (GI=36) or control (CON) (low energy sugar-free jelly) was given to the participant 2h before a 21-km performance run on a level treadmill. During each trial, 2 ml kg(-1) BM of 6.6% CHO-E solution was consumed immediately before exercise and every 2.5-km afterward. Blood samples were collected before (pre-meal), and 120 min after ingestion the meal (120 min), immediately (POST), and 60 min (POST-60 min) after exercise.

RESULTS

No difference was found in time to complete the 21-km run between LGI and HGI. The interleukin-6 (IL-6) level increased by more than 100 times immediately after exercise in the three trials and returned to the basal level only on LGI at POST-60 min. In contrast, interleukin-2 (IL-2) level showed a transitory decrease at POST on CON (p<0.001). Glucose concentrations did not recover to the pre-meal level by POST-60 min on HGI only. Cortisol concentrations increased throughout the exercise and were lower on LGI when compared with CON (p<0.05) at POST-60 min.

CONCLUSIONS

HGI and LGI demonstrated similar performance when CHO-E solution was consumed during a 21-km run. However, pre-exercise LGI meal attenuated the increases in cortisol and quickened the recovery of the increased IL-6 value.

Patient hydration: a major source of laboratory uncertainty

Movement of body water from compartment to compartment during any time period is attributable to forces active within and upon each space. The result of these forces leads to transfer of water between intravascular and extravascular compartments, as well as shifts between extracellular and intracellular spaces. The importance of these shifts and of the associated mechanism was described by Ernest Starling in 1896 in very much the same manner as it is viewed today. The end result of fluid transfer and its physiological and laboratory consequences has not been fully appreciated. Despite awareness that fluid shifts can affect laboratory analytical results, little recent investigation has addressed the problem in the routine clinical laboratory. Thus, the potential for significant misinterpretation remains. For example, it is known that individual laboratory test values can vary widely, depending on many factors including the subject's posture during and immediately before phlebotomy, leading to significant changes in the interpretation of blood analyte values. Furthermore, a variety of ubiquitous environmental effects have additional impact on fluid distribution and thus on test values. In other words, patient hydration status is a major pre-analytical variable that needs to be addressed by the clinical laboratory. The need to adjust data for patient hydration status is especially important in the case of colloid analytes for which the dynamic range includes a narrow "gray zone" where hydration changes of a few percentage points can change the clinical implications. The crucial importance of this adjustment is underscored by the fact that neither the testing laboratory nor the clinician are aware of this unseen circumstance and are thus compelled to work with data that do not necessarily reflect the clinical situation.

Fluids and hydration in prolonged endurance performance

Numerous studies have confirmed that performance can be impaired when athletes are dehydrated. Endurance athletes should drink beverages containing carbohydrate and electrolyte during and after training or competition. Carbohydrates (sugars) favor consumption and Na(+) favors retention of water. Drinking during competition is desirable compared with fluid ingestion after or before training or competition only. Athletes seldom replace fluids fully due to sweat loss. Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss. In contrast, hyperhydration or overdrinking before, during, and after endurance events may cause Na(+) depletion and may lead to hyponatremia. It is imperative that endurance athletes replace sweat loss via fluid intake containing about 4% to 8% of carbohydrate solution and electrolytes during training or competition. It is recommended that athletes drink about 500 mL of fluid solution 1 to 2 h before an event and continue to consume cool or cold drinks in regular intervals to replace fluid loss due to sweat. For intense prolonged exercise lasting longer than 1 h, athletes should consume between 30 and 60 g/h and drink between 600 and 1200 mL/h of a solution containing carbohydrate and Na(+) (0.5 to 0.7 g/L of fluid). Maintaining proper hydration before, during, and after training and competition will help reduce fluid loss, maintain performance, lower submaximal exercise heart rate, maintain plasma volume, and reduce heat stress, heat exhaustion, and possibly heat stroke.

The haemodynamic response to submaximal exercise during isovolaemic haemodialysis

INTRODUCTION

Exercise during haemodialysis has potential benefits but may compromise cardiovascular stability. We studied its acute effects on relative blood volume (RBV) and other haemodynamic parameters.

METHODS

Two groups of 10 patients were exercised submaximally using a stationary cycle during isovolaemic dialysis whilst RBV was monitored continuously. In study 1, patients exercised for two 10 min periods separated by 10 min rest. Cardiac output (CO), peripheral vascular resistance (PVR), central blood volume (CBV) and stroke volume were measured using ultrasound dilution immediately before and after each exercise session. In study 2, haemoglobin, serum total protein and albumin levels were measured before and immediately after the exercise session and at the nadir of the RBV trace.

RESULTS

RBV fell immediately on exercise initiation, the maximum reduction being 2.0+/-1.1% (after 5.9+/-1.4 min of exercise 1: P<0.001) and 2.0+/-1.2% (after 4.7+/-2.3 min of exercise 2: P<0.001). CO increased significantly after both periods of exercise (4.5+/-0.96 and 5.1+/-1.1 to 7.2+/-2.1 and 7.9+/-2.4 l/min, P<0.001 in both). Stroke volume increased significantly and PVR fell significantly during exercise. CBV increased in absolute terms but fell as a proportion of CO. Mean haemoglobin level at the RBV nadir was significantly higher than baseline (12.3+/-1.8 vs 11.8+/-1.7 g/dl: P<0.05: mean change 4.4+/-2.3%), as was mean total protein concentration (66.0+/-6.9 vs 62.0+/-8.1 g/l: P = 0.001: mean change 6.8+/-5.9%) and mean serum albumin concentration (36.0+/-3.9 vs 34.1+/-3.9 g/l: P<0.001: mean change 5.8+/-3.5%).

CONCLUSION

The haemodynamic response to exercise during haemodialysis is comparable with that in normal individuals. The rapid reduction in RBV on exercise occurs in spite of a significant increase in CO, mainly as a consequence of fluid shifts from the microvasculature to the interstitium.

Maximal oxygen uptake and lactate metabolism are normal in chronic fatigue syndrome

PURPOSE

Previous studies in chronic fatigue syndrome (CFS) have reported reductions in maximal oxygen uptake (VO(2max)), yet often the testing procedures have not followed accepted guidelines, and gender data have been pooled. The present study was undertaken to reevaluate exercise capacity in CFS patients by using "gold standard" maximal exercise testing methodology and stratifying results on a gender basis.

METHODS

Sixteen male and 17 female CFS patients and their gender-, age-, and mass-matched sedentary controls performed incremental exercise to volitional exhaustion on a stationary cycle ergometer while selected cardiorespiratory and metabolic variables were measured.

RESULTS

VO(2max) in male CFS patients was not different from control values (CFS: 40.5 +/- 6.7; controls: 43.3 +/- 8.6; mL x kg(-1) x min(-1)) and was 96.3 +/- 17.9% of the age-predicted value, indicating no functional aerobic impairment (3.7 +/- 17.9%). In female CFS patients, VO(2max) was lower than control values (CFS: 30.0 +/- 4.7; controls: 34.2 +/- 5.6; mL x kg(-1) x min(-1), P = 0.002), but controls were higher than the age-predicted value (112.6 +/- 15.4%, P = 0.008) whereas the CFS patients were 101.2 +/- 20.4%, indicating no functional aerobic impairment (-1.2 +/- 20.4%). Maximal heart rate (HR(max)) in male CFS patients was lower than their matched controls (CFS: 184 +/- 10; controls: 192 +/- 12; beats x min(-1); P = 0.016) but was 99.1 +/- 5.5% of their age-predicted value. In female CFS patients, HR(max) was not different from controls (CFS: 183 +/- 11; controls: 186 +/- 10; beats x min(-1)) and was 98.9 +/- 5.1% of the age-predicted value. The VO(2) at the lactate threshold (LT) in each gender group, whether expressed in mL x kg(-1) x min(-1) or as a percentage of VO(2max), was not different between CFS patients and controls.

CONCLUSIONS

In contrast to most previous reports, the present study found that VO(2max), HR(max), and the LT in CFS patients of both genders were not different from the values expected in healthy sedentary individuals of a similar age.

Dexamethasone in resting and exercising men. I. Effects on bioenergetics, minerals, and related hormones

A placebo and a low and a high dose of dexamethasone (Dex) were administered for 4.5 days, at 3-wk intervals, to 24 healthy men, following a double-blind, random-order, crossover procedure. After the last dose the subjects performed a maximal cycling exercise, during which respiratory exchanges, electrocardiogram, and blood pressures were monitored. Blood was sampled just before and after each exercise bout. Dex showed no significant effect on fitness, sleep, exhaustion during exercise, maximal O(2) consumption, ventilatory threshold, maximal blood lactate, or rest and exercise blood pressures. On the contrary, both doses of Dex significantly decreased heart rate at rest and during maximal exercise. Blood glucose at rest was higher after both doses of Dex than after placebo; the opposite was found during exercise. Blood levels of ACTH, beta-endorphin, cortisol, and cortisol-binding globulin were lowered by Dex at rest and after exercise. Dex stimulated the increase in atrial natriuretic factor during exercise and lowered rest and postexercise aldosterone. Finally, no difference between "fit or trained" and "less fit or untrained" subjects could be found with respect to Dex effects.

Whole blood and plasma water in health and disease: longitudinal and transverse observations and correlations with several different hematological and clinicochemical parameters

In a healthy reference population, hemoglobin (Hgb) and hematocrit (Hct) have been proposed as surrogate markers for whole blood water (WBW). We have extended this study under different physiological and pathological conditions in two longitudinal series, viz. (1) acute hyper- and hypohydration experiments in a healthy individual and (2) three athletes running 5 km each, and in three transverse series, viz. (3) a young reference population (n = 97, 49 females), (4) an old reference population (n = 37, nine females) consisting of inhabitants of a nursing home and (5) cardiac, hematological and renal patients including severe anaemia, polycythaemia and abnormal protein levels (n = 50, 25 females) with suspected hydration disturbances. The only sex difference found was a lower WBW in males in the young reference group. The percentage change of PW was less than that of WBW. In all five groups together (n = 293) WBW correlated closely (P < 0.0001) with Hgb and Hct (both r = -0.95) and with erythrocyte count (r = -0.85), whereas PW correlated with total protein (Tprot) (r = -0.84). In the longitudinally studied groups (1) and (2) WBW also correlated (P < 0.0001) with cholesterol, Ca, Tprot, albumin, platelets, globulin and white blood cells (r +/- 0.98-0.37), while PW correlated (P < 0.0001) not only with the same clinicochemical parameters but also with Hct, Hgb and red blood cells (r +/- 0.98-0.44). The homeostasis of PW is more narrowly regulated than that of WBW. Hgb, Hct and erythrocyte count reflect WBW and Tprot reflects PW also under disease conditions. WBW (mass%) can be calculated from Hgb and Hct using the formulae: -0.09 x Hgb (g/l) + 91.7 and -28.6 x Hct (v/v) + 91.8 and PW (mass%) from Tprot using the formula: -0.09 x Tprot (g/l) + 97.6. Other correlations were observed only in a longitudinal setting and presumably are due to concentration and dilution.

Water balance during and after marathon running

To describe the time course of plasma volume alterations and the changes in the plasma concentrations of hormones regulating water balance in relation to a marathon race, six experienced marathon runners (five men, one women) aged 28 (SD 6) years were studied during and for the 3 days following a treadmill marathon run at 68 (SD 5) percent of maximal oxygen consumption. Haematocrit, haemoglobin, plasma protein (Prot) and electrolyte (Na+, K+) concentration, osmolality (osm), plasma concentrations of renin (Ren), aldosterone (Ald) and atrial natriuretic peptide (ANP) were determined at rest in a sitting position (T(-30)), and then after 30 min in an upright posture (R(0)), while running a marathon at 10 km (R(10)), 30 km (R(30)) and 42.2 km (R end), and after the marathon at 30 min (T(30)), 60 min (T(60)), 120 min (T(120)) and 24 h (TD(+1)), 48 h (TD(+2)) and 72 h (TD(+3)). The changes in plasma volume (PV), Prot, osm and Na+ observed during the race were nonsignificant. Significant increases in plasma concentration of K+ [4.8 (SD 0.6) vs 5.5 (SD 0.6) mmol*1(-1); P <0.01], Ren [38(SD 57) vs 197 (SD 145) pmol*1(-1); P <0.02] and Ald [175 (SD 142) vs 1632 (SD 490) pmol*1(-1); P <0.01] were observed at R(end). A significant increase of ANP (P <0.05) was only found after R(10). Body mass significantly decreased by 2.0 kg (P <0.01) during the race in spite of the ingestion of 1.46 (SD 0.34)1 of a 5 percent glucose solution. Urinary volume and Na+ excretion dropped significantly after the completion of the marathon in comparison with the day before [2600 vs 1452 ml*day(-1)(P <0.02) and 161.3 vs 97.1 mmol*1(-1) (P <0.05)]. At TD(+1) and TD(+2) a significant increase in PV was noted, compared to T(-30). The lack of a decrease in PV during the marathon may have been due to the production of 402 g of metabolic water and by the release of 1280 g of water stored in glycogen complexes in muscle and liver. Thus, the hormone response during the marathon may have been due to the effects of the exercise itself and not to the effects of dehydration. The postmarathon PV expansion may be explained by a protein shift to the intravascular space and by renal sodium retention.

Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise

Red blood cell (RBC) susceptibility to oxidative and osmotic stress in vitro was investigated in cells from trained and untrained men before and after submaximal exercise. Whilst no significant change in peroxidative haemolysis occurred immediately after 1 h of cycling at 60% of maximal aerobic capacity (VO2max), a 20% increase was found 6h later in both groups (P < 0.05). The RBC osmotic fragility decreased by 15% immediately after exercise (P < 0.001) and this was maintained for 6h (P < 0.001). There was an associated decrease in mean cell volume (P < 0.05). Training decreased RBC susceptibility to peroxidative haemolysis (P < 0.025) but it did not influence any other parameter. These exercise-induced changes were smaller in magnitude but qualitatively similar to those found in haemopathological states involving haem-iron incorporation into membrane lipids and the short-circuiting of antioxidant protection. To explore this similarity, a more strenuous and mechanically stressful exercise test was used. Running at 75% VO2max for 45 min reduced the induction time of O2 uptake (peroxidation), consistent with reduced antioxidation capacity, and increased the maximal rate of O2 uptake in RBC challenged with cumene hydroperoxide (P < 0.001). The proportion of high-density RBC increased by 10% immediately after running (P < 0.001) but no change in membrane-incorporated haem-iron occurred. In contrast, treatment of RBC with oxidants (20-50 mumol.l-1) in vitro increased cell density and membrane incorporation of haem-iron substantially. These results showed that single episodes of submaximal exercise caused significant changes in RBC susceptibility to oxidative and osmotic stress. Such responses may account for the increase in RBC turnover found in athletes undertaking strenuous endurance training.