A field tool for the aerobic power evaluation of middle-aged female recreational runners.

This study used time to exhaustion (TTE) to predict V̇O2max in female recreational master runners. Forty-two middle-aged women (mean = 40.5 ± 5.9 years) who had trained for recreational running performed two Université de Montréal Track Tests in the facilities of the University of Barcelona (Spain). The first was performed on a treadmill (t), the second, on an athletics track (field: f). After measuring TTE and V̇O2max on the treadmill, a first-order equation was obtained to estimate fV̇O2max from fTTE. No significant difference was observed between the estimated fV̇O2max (46.5 ± 2.9 mL·kg-1·min-1) and the measured tV̇O2max (46.2 ± 5.3), with a mean value of the absolute differences of less than 8% of the tV̇O2max average. High agreement between the two V̇O2max values was also evident, as shown by the low bias of the differences and the Bland-Altman plot. The equation obtained is of interest to evaluate performance in middle-aged female recreational runners. It will allow coaches and runners to set running paces for training and could be used in training routines to determine improvements after a training program. Moreover, these tools could be used in the field to assess the physical fitness of middle-aged women, in efforts to preserve their health and physical function.

Intermittent hypobaric hypoxia combined with aerobic exercise improves muscle morphofunctional recovery after eccentric exercise to exhaustion in trained rats.

Unaccustomed eccentric exercise leads to muscle morphological and functional alterations, including microvasculature damage, the repair of which is modulated by hypoxia. We present the effects of intermittent hypobaric hypoxia and exercise on recovery from eccentric exercise-induced muscle damage (EEIMD). Soleus muscles from trained rats were excised before (CTRL) and 1, 3, 7, and 14 days after a double session of EEIMD protocol. A recovery treatment consisting of one of the following protocols was applied 1 day after the EEIMD: passive normobaric recovery (PNR), a 4-h daily exposure to passive hypobaric hypoxia at 4,000 m (PHR), or hypobaric hypoxia exposure followed by aerobic exercise (AHR). EEIMD produced an increase in the percentage of abnormal fibers compared with CTRL, and it affected the microvasculature by decreasing capillary density (CD, capillaries per mm2) and the capillary-to-fiber ratio (CF). After 14 days, AHR exhibited CD and CF values similar to those of CTRL animals (789 and 3.30 vs. 746 and 3.06) and significantly higher than PNR (575 and 2.62) and PHR (630 and 2.92). Furthermore, VEGF expression showed a significant 43% increase in AHR when compared with PNR. Moreover, after 14 days, the muscle fibers in AHR had a more oxidative phenotype than the other groups, with significantly smaller cross-sectional areas (AHR, 3,745; PNR, 4,502; and PHR, 4,790 µm2), higher citrate synthase activity (AHR, 14.8; PNR, 13.1; and PHR, 12 µmol·min-1·mg-1) and a significant 27% increment in PGC-1α levels compared with PNR. Our data show that hypoxia combined with exercise attenuates or reverses the morphofunctional alterations induced by EEIMD.NEW & NOTEWORTHY Our study provides new insights into the use of intermittent hypobaric hypoxia combined with exercise as a strategy to recover muscle damage induced by eccentric exercise. We analyzed the effects of hypobaric exposure combined with aerobic exercise on histopathological features of muscle damage, fiber morphofunctionality, capillarization, angiogenesis, and the oxidative capacity of damaged soleus muscle. Most of these parameters were improved after a 2-wk protocol of intermittent hypobaric hypoxia combined with aerobic exercise.

Sildenafil does not Improve Exercise Capacity under Acute Hypoxia Exposure.

The increase in pulmonary arterial pressure (PAP) due to hypoxic pulmonary vasoconstriction (HPV) could be a limiting factor for physical performance during hypoxic exposure. Sildenafil has been shown to reduce PAP in situations of moderate or severe hypoxia, and consequently its role as an ergogenic aid and even a possible doping substance must be considered. We performed a double-blind crossover study to determine the effects of sildenafil on cardiovascular, respiratory and metabolic parameters in normoxia and during acute exposure to hypobaric hypoxia (4 000 m) at rest and during maximal and submaximal (60% VO2 max) exercise tests. One hour before testing started, sildenafil (100 mg) or a placebo was orally administered to 11 volunteers. In normoxic conditions, sildenafil did not affect performance. Similarly, no significant differences were found in cardiovascular and respiratory parameters in hypoxic conditions at rest or during exercise. The use of sildenafil to improve physical performance in non-acclimatized subjects is not supported by our data.

Anaerobic training in hypoxia: A new approach to stimulate the rating of effort perception.

This study compared subjective effort perception with objective physiological measures during high-intensive intermittent exercise performed in normoxia, moderate hypoxia (FiO2: 16.5%) and severe hypoxia (FiO2: 13.5%). Sixteen physically active subjects performed an equal training session on three different days. Training consisted of 6 "all-out" series of continuous jumps lasting for 15s each. Average power output during the jumps was similar in all three conditions (~3200W). Greater hypoxemia was observed in hypoxia as compared to normoxia. Likewise, a significantly higher value in perceived effort was observed after hypoxia training as compared to normoxia training (p<0.05). Whereas blood lactate concentrations immediately after training were not different between normoxia and hypoxia, creatine kinase increased in moderate (p=0.02) and severe (p<0.01) hypoxia compared to normoxia 24h after the training. Perceived fatigue was also significantly elevated 24h after hypoxic exercise only. Heart rate variability pre and 24h after exercise showed a tendency to sympathetic predominance in severe hypoxia as compared to moderate hypoxia and normoxia. In conclusion, a single session of anaerobic exercise can be executed at the same intensity in moderate/severe hypoxia as in normoxia. This type of hypoxic training may be considered as a method potentially to improve the ability tolerating discomfort and consequently also exercise performance.

A semiquantitative scoring tool to evaluate eccentric exercise-induced muscle damage in trained rats.

Unaccustomed eccentric exercise is a well-documented cause of exercise-induced muscle damage. However, in trained subjects muscle injury involves only light or moderate tissue damage. Since trained rats are widely used as a model for skeletal muscle injury, here we propose a semiquantitative scoring tool to evaluate muscle damage in trained rats. Twenty male Sprague-Dawley rats were trained fortwo weeks following a two-week preconditioning period, and randomly divided into two groups: control rats (CTL; n=5) and rats with eccentric exercise-induced muscle damage (INJ; n=15). Injured rats were sacrificed at three time points: 1, 3 and 7 days post injury (n=5 each). Transverse sections from the right soleus were cut (10 µm) and stained with haematoxylin-eosin. Samples were evaluated by two groups of observers (four researchers experienced in skeletal muscle histopathology and four inexperienced) using the proposed tool, which consisted of six items organised in three domains: abnormal fibre morphology, necrotic/(re)degenerating fibres (muscle fibre domain), endomysial and perimysial infiltration (inflammatory state domain) and endomysium and perimysium distension (interstitial compartment domain). We observed the expected time course in the six evaluated items. Furthermore, agreement among observers was evaluated by measuring the Intraclass Correlation Coefficient (ICC). Within the experienced group, items from the muscle fibre and interstitial compartment domains showed good agreement and the two items from the infiltration compartment domain showed excellent agreement. in conclusion, the proposed tool allowed quick and correct evaluation of light to moderate muscle damage in trained rats with good agreement between observers.

Popularity of hypoxic training methods for endurance-based professional and amateur athletes.

Scientific debate continues into whether hypoxic training has any performance benefit for athletes, and although this type of training seems popular, to our knowledge little empirical evidence on its popularity with endurance-based athletes exists. To quantify the usage of hypoxic training in endurance-based athletes we asked 203 athletes (amateur = 108, professional = 95) to complete a 17-question survey during 2013-2014 season. Compared to amateurs, professional athletes were 4.5 times (3.0-6.8, odds ratio, 95% confidence limits) more likely to undertake hypoxic training. Live-high train-low was the most popular hypoxic training protocol for athletes (52% professional and 80% amateur) with live-high train-high also used (38% professional, 20% amateur). Compared to amateurs, professional athletes tended to use evidence-based hypoxic training methods, seek advice on hypoxic training from reliable sources and were generally more realistic about the potential performance gains as a result of hypoxic training. Almost one third (25-30%) of all athletes suffered illness during their hypoxic training. Compared to amateurs, professional athletes are more likely to undertake hypoxic training and tend to follow current scientific guidelines. Attenuation of the ill effects that occur during hypoxic training may be accomplished if athletes give more attention to monitoring stress and training levels.

Sex-linked differences in pulse oxymetry.

The difference between genders has generated increasing interest in recent years. It is well known that women and men show differences in their respiratory system: different red blood cell counts, haemoglobin and 2,3-diphosphoglycerate plasma concentrations. Recently, further differences have been found in the ventilatory response to hypoxia and exercise and the evolution of some respiratory illnesses. In this study it was found that during rest at sea level, the haemoglobin oxygen saturation, as measured by pulse oxymetry, is slightly higher in women than in men (98.6 (SD 1.1)% versus 97.9 (SD 0.9)%; p = 0.001). These findings are consistent with other studies, which found gender differences in the transcutaneous or tissue PaO(2). The difference in oxygen saturation is not related to differences in ventilation. The disparity is modest and does not seem to produce great differences in the oxygen content of arterial blood, but combined with the different affinity of haemoglobin for oxygen or different metabolic rate, may play a role in the course of elite competition sports, high altitude ascents or the evaluation of critically ill patients. Further studies are needed to establish the degree, extent and clinical importance of these differences in the saturation of haemoglobin.

Hemorheology and oxygen transport in vertebrates. A role in thermoregulation?

We studied the effect of temperature on blood rheology in three vertebrate species with different thermoregulation and erythrocyte characteristics. Higher fibrinogen proportion to total plasma protein was found in turtles (20%) than in pigeons (5.6%) and rats (4.2%). Higher plasma viscosity at room temperature than at homeotherm body temperature was observed in rats (1.69 mPa x s at 20 degrees C vs. 1.33 mPa x s at 37 degrees C), pigeons (3.40 mPa x s at 20 degrees C vs. 1.75 mPa x s at 40 degrees C), and turtles (1.74 mPa x s at 20 degrees C vs. 1.32 mPa x s at 37 degrees C). This fact allow us to hypothesize that thermal changes in protein structure may account for an adjustment of the plasma viscosity. Blood viscosity was dependent on shear rate, temperature and hematocrit in the three species. A different behaviour in apparent and relative viscosities between rat and pigeon at environmental temperature was found. Moreover, the blood oxygen transport capacity seems more affected by a reduction of temperature in rats than in pigeons. Both findings indicate a greater influence of temperature on mammalian erythrocyte than on nucleated red cells, possibly as a consequence of differences in thermal sensitivity and mechanical stability between them. A comparison between the three species revealed that apparent blood viscosity measured at homeotherm physiological temperature was linearly related to the hematocrit level of each species. However, when measured at environmental temperature, rat blood showed a higher apparent viscosity than those found in species with non-nucleated red cells, thus indicating a higher impact of temperature decrease on blood viscosity in mammals. This suggest that regional hypothermia caused by cold exposure may affect mammalian blood rheological behaviour in a higher extent than in other vertebrate species having nucleated red cells and, consequently, influencing circulatory function and oxygen transport.

Increased blood ammonia in hypoxia during exercise in humans.

The effect of acute hypoxia on blood concentration of ammonia ([NH3]b) and lactate (la-]b) was studied during incremental exercise(IE), and two-step constant workload exercises (CE). Fourteen endurance-trained subjects performed incremental exercise on a cycle ergometer under normoxic (21% O2) and hypoxic (10.4% O2) conditions. Eight endurance-trained subjects performed two-step constant workload exercise at sea level and at a simulated altitude of 5000 m (hypobaric chamber, P(B)=405 Torr; P(O2)=85 Torr) in random order. In normoxia, the first step lasted 25 minutes at an intensity of 85 % of the individual ventilatory anaerobic threshold (AT(vent), ind) at sea level. This reduced workload was followed by a second step of 5 minutes at 115% of their AT(vent), ind. This test was repeated into a hypobaric chamber, at a simulated altitude of 5,000 m. The first step in hypoxia was at an intensity of 65 % of AT(vent), ind., whereas workload for the second step at simulated altitude was the same as that of the first workload in normoxia (85 % of AT(vent), ind). During IE, [NH3]b and [la-]b were significantly higher in hypoxia than in normoxia. Increases in these metabolites were highly correlated in each condition. The onset of [NH3]b and [la-]b accumulation occurred at different exercise intensity in normoxia (181W for lactate and 222W for ammonia) and hypoxia (100W for lactate and 140W for ammonia). In both conditions, during CE, [NH3]b showed a significant increase during each of the two steps, whereas [la-]b increased to a steady-state in the initial step, followed by a sharp increase above 4 mM x L(-1) during the second. Although exercise intensity was much lower in hypoxia than in normoxia, [NH3]b was always higher at simulated altitude. Thus, for the same workload, [NH3]b in hypoxia was significantly higher (p<0.05) than in normoxia. Our data suggest that there is a close relationship between [NH3]b and [la-]b in normoxia and hypoxia during graded intensity exercises. The accumulation of ammonia in blood is independent of that of lactate during constant intense exercise. Hypoxia increases the concentration of ammonia in blood during exercise.

Erythropoietin acute reaction and haematological adaptations to short, intermittent hypobaric hypoxia.

This study aimed to determine whether brief hypoxic stimuli in a hypobaric chamber are able to elicit erythropoietin (EPO) secretion, and to effectively stimulate erythropoiesis in the short term. In two different experiments, a set of haematological, biochemical, haemorheological, aerobic performance, and medical tests were performed in two groups of healthy subjects. In the first experiment, the mean plasma concentration of EPO ([EPO]) increased from 8.7 to 13.5 mU.ml-1 (55.2%; P < 0.01) after 90 min of acute exposure at 540 hPa, and continued to rise until a peak was attained 3 h after the termination of hypoxia. In the second experiment, in which subjects were exposed to a simulated altitude of up to 5500 m (504 hPa) for 90 min, three times a week for 3 weeks, all haematological indicators of red cell mass increased significantly, reaching the highest mean values at the end of the programme or during the subsequent 2 weeks, including packed cell volume (from 42.5 to 45.1%; P < 0.01), red blood cell count (from 4.55 x 10(6) to 4.86 x 10(6).l-1; P < 0.01), reticulocytes (from 0.5 to 1.4%; P < 0.01), and haemoglobin concentration (from 14.3 to 16.2 g.dl-1; P < 0.01), without an increase in blood viscosity. Arterial blood oxygen saturation during hypoxia was improved (from 60% to 78%; P < 0.05). Our most relevant finding is the ability to effectively stimulate erythropoiesis through brief intermittent hypoxic stimuli (90 min), in a short period of time (3 weeks), leading to a lower arterial blood desaturation in hypoxia. The proposed mechanism for these haematological and functional adaptations is the repeated triggering effect of EPO production caused by the intermittent hypoxic stimuli.

Acclimatization near home? Early respiratory changes after short-term intermittent exposure to simulated altitude.

OBJECTIVE: With the ultimate goal of finding a straightforward protocol for acclimatization at simulated altitude, we evaluated the early effects of repeated short-term exposure to hypobaric hypoxia on the respiratory response to exercise in hypoxia. METHODS: Nine subjects were exposed to a simulated altitude of 5000 m for 2 hours a day for 14 days. Arterial oxygen saturation (SaO2), expired volume per minute (VE), respiratory rate, tidal volume (VT), and heart rate were measured during rest and during exercise (cycloergometer, at 30% of maximum oxygen consumption at sea level), both in normoxia and at 5000 m of simulated altitude on the first and 15th days. On the same days, blood samples were obtained for hematological tests. RESULTS: During exercise in hypoxia, SaO2 rose from 65 to 71% (P = .02), and VE rose from 55.5 to 67.6 L.min-1 (P = .02) due to an increase in VT from 2 to 2.6 L (P = .003). No significant differences were found in any of the variables studied at rest either in normoxia or in hypoxia or in exercise in normoxia after the exposure program. In the second week, changes in packed cell volume and blood hemoglobin concentration were nonsignificant. CONCLUSIONS: After short-term intermittent exposure to hypobaric hypoxia, subjects increased their ventilatory response and SaO2 during exercise at simulated altitude. These changes may be interpreted as acclimatization to altitude. The monitoring of ventilatory response and SaO2 during moderate exercise in hypobaric hypoxia may be used to detect the first stages of acclimatization to altitude.

Intermittent hypobaric hypoxia induces altitude acclimation and improves the lactate threshold.

The physiological responses to short-term intermittent exposure to hypoxia in a hypobaric chamber were evaluated. The exposure to hypoxia was compatible with normal daily activity. The ability of the hypoxia program to induce hematological and ventilatory adaptations leading to altitude acclimation and to improve physical performance capacity was tested. Six members of a high-altitude expedition were exposed to intermittent hypoxia and low-intensity exercise (in cycle-ergometer) in the INEFC-UB hypobaric chamber over 17 d, 3-5 h x d(-1), at simulated altitude of 4,000 m to 5,500 m. Following this hypoxia exposure program, significant increases were found in packed cell volume (41 to 44.6%; p<0.05), red blood cells count (4.607 to 4.968 10(6) cells x microL(-1); p<0.05), and hemoglobin concentration (14.8 to 16.4 g x dL(-1); p<0.05), thus implying an increase in the blood oxygen transport capacity. Significant differences in exercise blood lactate kinetics and heart rate were also observed. The lactate vs. exercise load curve shifted to the right and heart rate decreased, thus indicating an improvement of aerobic endurance. These results were associated with a significant increase in the ventilatory anaerobic threshold (p<0.05). Significant increases (p<0.05) in pulmonary ventilation, tidal volume, respiratory frequency, O2 uptake, CO2 output and ventilatory equivalents to oxygen (VE/Vo2) and carbon dioxide (VE/co2) were observed at the ventilatory threshold and within the transitional zone of the curves. We conclude that short-term intermittent exposure to moderate hypoxia, in combination with low-intensity exercise in a hypobaric chamber, is sufficient to improve aerobic capacity and to induce altitude acclimation.

Intermittent hypobaric hypoxia stimulates erythropoiesis and improves aerobic capacity.

PURPOSE: The purpose of the study was to examine the effect of a very short intermittent exposure to moderate hypoxia in a hypobaric chamber on aerobic performance capacity at sea level and the erythropoietic response. The effects of hypobaric hypoxia alone and combined with low-intensity exercise were also compared. METHODS: Seventeen members of three high-altitude expeditions were exposed to intermittent hypoxia in a hypobaric chamber over 9 d at simulated altitude, which was progressively increased from 4000 to 5500 m in sessions ranging from 3 to 5 h x d(-1). One group (N = 7; HE group) combined passive exposure to hypoxia with low-intensity exercise on a cycle ergometer. Another group (N = 10; H group) was only exposed to passive hypoxia. Before and after the exposure to hypoxia, medical status, performance capacity, and complete hematological and hemorheological profile of subjects were evaluated. RESULTS: No significant differences were observed between the two groups (HE vs H) in any of the parameters studied, indicating that hypoxia alone was responsible for the changes. After the acclimation period, a significant increase in exercise time (mean difference: +3.9%; P < 0.01), and maximal pulmonary ventilation (+5.5%; P < 0.05) was observed during the maximal incremental test at sea level. Individual lactate-velocity curves significantly shifted to the right (P < 0.05), thus revealing an improvement of aerobic endurance. A significant increase was found in PCV (42.1-45.1%; P < 0.0001), RBC count (5.16 to 5.79 x 10(6) x mm(-3); P < 0.0001), reticulocytes (0.5 to 1.1%; P < 0.0001) and hemoglobin (Hb) concentration (14.2 to 16.7 g x dL(-1); P < 0.002). CONCLUSIONS: It was concluded that short-term hypobaric hypoxia can activate the erythropoietic response and improve the aerobic performance capacity in healthy subjects.

Effect of temperature on oxygen stores during aerobic diving in the freshwater turtle Mauremys caspica leprosa.

Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15 degrees, 25 degrees, and 35 degrees C) and during the thermal transient (30 degrees-15 degrees C) induced by immersion in cold water. The term "aerobic dive limit" has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15 degrees C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30 degrees-15 degrees C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.

Hematological, electrolyte, and biochemical alterations after a 100-km run.

Seven well-trained male long-distance runners were studied during a 100-km road race. Hematologic parameters, plasma electrolytes, glucose, lactate, urea, and creatinine content in plasma and the activity of the enzymes gamma-glutamyltransferase and creatinine kinase were determined before and after the race. A slight increase in hematocrit was found after the race, although the red blood cell count and hemoglobin concentration remained unchanged. Further, a significant rise in the number of white blood cells, lymphocytes, and neutrophils was found after the race. Postrun concentrations of plasma sodium and potassium increased significantly from 142 +/- 7 to 161 +/- 7 mmol.L-1, and from 4.22 +/- 0.37 to 5.15 +/- 0.46 mmol.L-1 (p < 0.05), respectively. Plasma concentrations of lactate (1.29 +/- 0.31 vs. 3.57 +/- 1.22 mmol.L-1), urea (6.09 +/- 1.0 vs. 8.35 +/- 1.35 mmol.L-1), creatinine (73.4 +/- 3.5 vs. 117.6 +/- 19.4 mumol.L-1), plasma creatine kinase (91.1 +/- 25.1 vs. 2843 +/- 2341 IU.L-1), and gamma-glutamyltransferase (20.28 +/- 1.88 vs. 24.14 +/- 4.09 IU .L-1) increased significantly (p < 0.05) after the run. It was concluded that during ultralong-distance races, acute renal dysfunction and muscle damage could contribute to the observed hypernatremia and hyperkalemia.

Changes in blood ammonia and lactate levels during a triathlon race.

Blood ammonia and lactate concentrations were analyzed in 7 volunteer male athletes before and immediately after each segment of an endurance triathlon. The purpose of this study was to examine the effects of triathlon on ammonia and lactate blood levels and the possible correlation between both in each different event. Concentrations of blood ammonia were increased after each of the three segments, reaching a peak after the 40 km bicycle ride. Concentrations of blood lactate were also increased over baseline. However, there was a higher increase after the 1.4 km lake swim, than after the 40 km bicycle ride or after the 10 km run. No correlation was found between the levels of ammonia and lactate, suggesting that ammonia and lactate follow different metabolic patterns.

Respiratory gas exchange using a triaxial alveolar gas diagram.

A triaxial alveolar gas diagram to depict fractional concentration of oxygen, carbon dioxide and nitrogen is described, in which the R = 1 line is always implicit. Although it is not claimed that this representation leads to new insights into respiratory physiology, a method of plotting on a triaxial coordinate system has been found to be well suited to many applications when a direct display of fractional nitrogen concentration is required.

A method for sampling representative muscular venous blood during exercise in rats.

A technique for chronic cannulation of the muscular branch of the femoral vein in the rat is described. The method was validated by the application of vascular corrosion casts and comparative analysis of lactate concentration with mixed venous blood and arterial samples taken through the cannulas during lower hindlimb muscle contraction in anaesthetized rats.

Plasma and red blood cell magnesium levels and plasma creatinine after a 100 km race.

Magnesium homeostasis is critical for exercise performance. In this report the effect of long distance race on the erythrocyte and plasma magnesium concentration is determined in a group of 7 well-trained male amateur runners. After a 100 km race the plasma Mg2+ levels increased significantly from 0.845 +/- 0.074 to 0.934 +/- 0.099 mmol.l-1 (p < 0.05). However, the intra-erythrocyte Mg2+ concentrations were not modified significantly (2.10 +/- 0.2 mmol.l-1 versus 2.14 +/- 0.12 mmol.l-1). Creatinine plasma levels increased significantly from 73.4 +/- 3.5 mumol.l-1 to 117.6 +/- 19.4 mumol.l-1 (p < 0.01), suggesting impairment of the renal function. A significant positive correlation between plasma magnesium and plasma creatinine, r = +0.65 (p < 0.01) was found. These results suggest that an increase in the magnesium plasma levels could be related to renal failure during long-distance running.