The influence of endurance exercise on the antioxidative status of human skin

Oxidative stress is supposed to be responsible for a diversity of diseases. For protection purposes, the human organism exhibits a line-up of antioxidant substances functioning as radical catchers. As a result of neutralization of free radicals, antioxidants are destroyed. Therefore, the degradation of the antioxidants can be utilized as an indirect parameter for the measurement of free radical formation. As physical exercise may also induce oxidative stress, the aim of the present study was to determine the antioxidant substances, and more precisely, the carotenoid concentration in the skin of male volunteers during different sportive exposures (cycling and running with two different exercise intensities) with resonance Raman spectroscopic measurements. The results revealed that moderate and high intensity cycling and running decrease the carotenoid concentration of the skin, whereas both sport disciplines and both exercise intensities revealed similar results. It can be concluded that above a certain threshold, physical exercise leads to oxidative stress also in the skin associated with the decrease in the antioxidant concentration. This gives rise to the impairment of the first defence line of the skin and means an increase in the risk of sun exposure-induced damage, e.g., when exercise training is performed outside. Nevertheless, it has to be emphasized that sport in general applied at moderate loads has predominantly positive effects on the health of humans especially concerning cardiovascular and metabolic diseases.     

Glucose utilization during exercise: influence of endurance training

During exercise skeletal muscle glucose utilization is higher than at rest. This is due to the combined effect of an increase in glucose supply, increased surface membrane glucose transport capacity and increased muscle glucose metabolism during exercise. The kinetics of glucose utilization in skeletal muscle during exercise in humans show an apparent K_m of ～10 mM , indicating that changes in the blood glucose concentration around the physiological level of ～5 mM almost linearly translate into changes in muscle glucose utilization. The signalling events responsible for increased glucose transport in contracting muscle are not well understood, although calcium seems to be involved. Contractions do not utilize the proximal part of the insulin signalling cascade to activate glucose transport, because contractions do not cause phosphorylation of insulin receptor substrate 1 or activation of phosphatidylinositol 3-kinase. Endurance training leads to a decrease in glucose utilization during submaximal exercise of a given absolute submaximal power output in spite of a large increase in the total muscle GLUT4 content. The molecular mechanism behind this decrease in glucose utilization seems to be blunted exercise-induced translocation of GLUT4 protein to the sarcolemma, in turn blunting the exercise-induced increase in sarcolemmal glucose transport capacity.     

The influence of hydration status on stress-induced hemoconcentration

This study examined the effects of hydration status on rheological and hemodynamic activity during rest, mental stress, postural stress, and combined mental/postural stress in 24 men when euhydrated and hyperhydrated. The stress tasks elicited hemoconcentration, although the effects were less pronounced during mental stress. Hyperhydration was associated with higher plasma volume throughout. All stress tasks also perturbed hemodynamic activity, irrespective of hydration status, with the exception of heart rate reactivity, which was attenuated when hyperhydrated. As expected the combined stress during euhydration was associated with an unfavorable rheological and cardiovascular profile, which may help explain the increased incidence of cardiovascular events in the morning.     

The effect of hydration status on plasma vasopressin release during physical exercise in man

The effect of hydration status on plasma vasopressin release was studied in six healthy volunteers undergoing a 15-min bicycle ergometer exercise. The hydration states were dehydration, produced by a 14-h abstinence from fluids, euhydration, and hyperhydration caused by drinking 20 ml kg-1 water 2 h before the exercise. The exercise load was individually adjusted to 70% of maximal oxygen uptake. Exercise resulted in a significant increase in plasma vasopressin only during euhydration, in spite of the marked increase in plasma osmolality in all hydration states. The vasopressin concentrations during hyperhydration were significantly lower than during euhydration. Plasma volume and serum sodium were significantly affected by the exercise. The highest responses were obtained in euhydration and the lowest in hyperhydration. On this basis, the body's drive towards normal homeostasis and to the best ability to respond to the challenges of the environment is rational.     

Changes in salivary antimicrobial peptides,immunoglobulin A and cortisol after prolonged strenuous exercise

The aim of the present study was to examine whether amount of oral antimicrobial components, human β-defensin-2 (HBD-2), cathelicidin (LL-37), and immunoglobulin A (IgA), might be affected by prolonged strenuous exercise. Ten young male volunteers either exercised on recumbent ergometer at 75% [(V)\dot]\textO_2max \dot{V}{\text{O}}_{{2\max }} for 60 min (exercise session) or sat quietly (resting session). Saliva samples were obtained at 60-min intervals during sessions for measurements of saliva antimicrobial components (HBD-2, LL-37, and IgA), saliva cortisol and osmolality. Saliva flow rate was decreased and saliva osmolality was increased during the 60-min exercise. Saliva HBD-2 and LL-37 concentrations and secretion rates were increased during and after the exercise, whereas saliva IgA concentration and secretion rates were decreased after the exercise. Saliva cortisol was increased during and after the exercise. The areas under the curve of the time courses of saliva levels of HBD-2 and LL-37 were negatively correlated with those of cortisol levels in saliva. The present findings suggested that a single bout of prolonged strenuous exercise caused a transient increase in the oral HBD-2 and LL-37 levels.     

Effect of endurance training on liver cAMP response to prolonged submaximal exercise

Endurance-trained rats utilize liver glycogen at a reduced rate during exercise compared to nontrained rats. We have compared liver cAMP responses to exercise in trained and nontrained rats in an attempt to elucidate the mechanism of this adaptation. Rats were trained on a motor-driven rodent treadmill 5 days/wk for 12 wk. On the day of the test, trained and nontrained rats were quickly anesthetized after running at 21 m/min up a 15% grade for periods up to 90 min. After 45 min of running, liver cAMP had increased from 0.60 +/- 0.01 to 0.90 +/- 0.03 pmol/mg in nontrained rats whereas no significant increase had occurred in livers of trained rats. Plasma glucagon and norepinephrine levels were significantly lower in trained rats at this point. At the end of 90 min hepatic cAMP was 1.28 +/- 0.12 in nontrained compared to 0.83 +/- 0.06 pmol/mg in trained rats. Plasma glucagon was markedly elevated in nontrained but not in trained rats at this time. The lower rate of liver glycogen utilization in trained rats is consistent with the lower cAMP levels maintained early in exercise.     

The effects of heat stress on neuromuscular activity during endurance exercise

This study analysed the effect of hot (35 degrees C) and cold (15 degrees C) environments on electromyographic (EMG) signal characteristics, skin and rectal temperatures and heart rate during progressive endurance exercise. Eight healthy subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak sustained power output and then cycled at increasing (15 W/min) work rates to exhaustion in both 35 degrees C and 15 degrees C environments. Skin and rectal temperatures, heart rate and EMG data were measured during the trials. The skin temperatures were higher and the subjects felt more uncomfortable in the hot conditions (Bedford scale) ( P<0.01). Rectal temperature was slightly, but not significantly, higher under hot conditions. Heart rate was significantly higher in the hot group (between condition P<0.05). Peak power output (267.4+/-67.7 W vs. 250.1+/-61.5 W) and time-to-exhaustion (55.7+/-16.7 min vs. 54.5+/-17.1 min) (COLD vs. HOT) were not different between conditions. There were no differences in integrated EMG (IEMG) or mean power frequency spectrum between conditions. Rating of perceived exertion increased similarly in both conditions over time. Although the hot conditions increased heart rate and skin temperature, there were no differences in muscle recruitment or maximal performance, which suggests that the thermal stress of 35 degrees C, in combination with exercise, did not impair maximal performance in this study.     

Effects of aerobic endurance training status and specificity on oxygen uptake kinetics during maximal exercise

The main purpose of this study was to analyze the effects of exercise mode, training status and specificity on the oxygen uptake (O₂) kinetics during maximal exercise performed in treadmill running and cycle ergometry. Seven runners (R), nine cyclists (C), nine triathletes (T) and eleven untrained subjects (U), performed the following tests on different days on a motorized treadmill and on a cycle ergometer: (1) incremental tests in order to determine the maximal oxygen uptake (O_2max) and the intensity associated with the achievement of O_2max (IO_2max); and (2) constant work-rate running and cycling exercises to exhaustion at IO_2max to determine the effective time constant of the O₂ response (O₂). Values for O_2max obtained on the treadmill and cycle ergometer [R=68.8 (6.3) and 62.0 (5.0); C=60.5 (8.0) and 67.6 (7.6); T=64.5 (4.8) and 61.0 (4.1); U=43.5 (7.0) and 36.7 (5.6); respectively] were higher for the group with specific training in the modality. The U group showed the lowest values for O_2max, regardless of exercise mode. Differences in O₂ (seconds) were found only for the U group in relation to the trained groups [R=31.6 (10.5) and 40.9 (13.6); C=28.5 (5.8) and 32.7 (5.7); T=32.5 (5.6) and 40.7 (7.5); U=52.7 (8.5) and 62.2 (15.3); for the treadmill and cycle ergometer, respectively]; no effects of exercise mode were found in any of the groups. It is concluded that O₂ during the exercise performed at IO_2max is dependent on the training status, but not dependent on the exercise mode and specificity of training. Moreover, the transfer of the training effects on O₂ between both exercise modes may be higher compared with O_2max.     

Relationship between stress hormones and testosterone with prolonged endurance exercise

Previous pharmacological and pathological studies have reported negative relationships between circulating testosterone and certain stress hormones (i.e., cortisol and prolactin) in humans. These relationships have subsequently been used in hypotheses explaining the subclinical resting testosterone levels often found in some endurance-trained males, but as of yet no one has specifically examined these relationships as they relate to exercise. Thus, we examined the relationship between total and free testosterone levels and cortisol, and between total and free testosterone and prolactin following prolonged endurance exercise in trained males. Twenty-two endurance-trained males volunteered to run at 100% of their ventilatory threshold (VT) on a treadmill until volitional fatigue. Blood samples were taken at pre-exercise baseline (B0); volitional fatigue (F0); 30 min (F30), 60 min (F60), and 90 min (F90) into recovery; and at 24 h post-baseline (P24 h). At F0 [mean running time = 84.8 (3.8) min], exercise induced significant changes (P<0.05) from B0 in total testosterone, cortisol and prolactin. All three of these hormones were still significantly elevated at F30; but at F60 only cortisol and prolactin were greater than their respective B0 values. Free testosterone displayed no significant changes from B0 at F0, F30, or the F60 time point. At F90, neither cortisol nor prolactin was significantly different from their B0 values, but total and free testosterone were reduced significantly from B0. Cortisol, total testosterone and free testosterone at P24 h were significantly lower than their respective B0 levels. Negative relationships existed between peak cortisol response (at time F30) versus total testosterone (at F90, r=–0.53, P<0.05; and at P24 h, r=–0.60, P<0.01). There were no significant relationships between prolactin and total or free testosterone. In conclusion, the present findings give credence to the hypothesis suggesting a linkage between the low resting testosterone found in endurance-trained runners and stress hormones, with respect to cortisol.     

Effect of ambient temperature on caffeine ergogenicity during endurance exercise

It is well established that caffeine ingestion during exercise enhances endurance performance. Conversely, the physiological and psychological strain that accompanies increased ambient temperature decreases endurance performance. Little is known about the interaction between environmental temperature and the effects of caffeine on performance. The purpose of this study was to compare the effects of ambient temperature (12 and 33°C) on caffeine ergogenicity during endurance cycling exercise. Eleven male cyclists (mean ± SD; age, 25 ± 6 years; [(V)\dot] \textO_2max , {\dot V \text{O}}_{2\max } , 58.7 ± 2.9 ml kg⁻¹ min⁻¹) completed four exercise trials in a randomized, double blind experimental design. After cycling continuously for 90 min (average 65 ± 7% [(V)\dot] \textO_2max {\dot V \text{O}}_{2\max } ) in either a warm (33 ± 1°C, 41 ± 5%rh) or cool (12 ± 1°C, 60 ± 7%rh) environment, subjects completed a 15-min performance trial (PT; based on total work accumulated). Subjects ingested 3 mg kg⁻¹ of encapsulated caffeine (CAF) or placebo (PLA) 60 min prior to and after 45 min of exercise. Throughout exercise, subjects ingested water so that at the end of exercise, independent of ambient temperature, their body mass was reduced 0.55 ± 0.67%. Two-way (temperature × treatment) repeated-measures ANOVA were conducted with alpha set at 0.05. Total work (kJ) during the PT was greater in 12°C than 33°C [P < 0.001, η² = 0.804, confidence interval (CI): 30.51–62.30]. When pooled, CAF increased performance versus PLA independent of temperature (P = 0.006, η² = 0.542 CI: 3.60–16.86). However, performance differences with CAF were not dependent on ambient temperature (i.e., non-significant interaction; P = 0.662). CAF versus PLA in 12 and 33°C resulted in few differences in other physiological variables. However, during exercise, rectal temperature (T _re) increased in the warm environment (peak T _re; 33°C, 39.40 ± 0.45; 12°C, 38.79 ± 0.42°C; P < 0.05) but was not different in CAF versus PLA (P > 0.05). Increased ambient temperature had a detrimental effect on cycling performance in both the CAF and PLA conditions. CAF improved performance independent of environmental temperature. These findings suggest that caffeine at the dosage utilized (6 mg/kg body mass) is a, legal drug that provides an ergogenic benefit in 12 and 33°C.     

Role of taurine in osmoregulation during endurance exercise

Taurine is released by contracting muscles, but its actual role remains unspecified. In this study, we investigated whether the exercise-stimulated release of taurine from muscle into the plasma regulates the modification of osmolality induced by intramuscular osmolyte production. Six subjects performed 90 min of cycling exercise (at 70% maximum power output) on two occasions, with (HC) or without (DC) fluid intake. Taurine content was determined in plasma, blood cells and urine before and after the endurance events, together with plasma osmolality. Plasma osmolality increased by 4% in the DC experiment (P<0.01), but remained stable in the HC condition. The exercise also induced changes in the mean (SD) plasma taurine content to a greater degree in HC [+63 (26)%] than in DC [+33 (18)%; P<0.05], supporting the hypothesis that taurine is released into the plasma via an osmoregulatory process. However, the higher plasma taurine content in HC was not related to changes in renal taurine. In addition, the increase of taurine in plasma was not related to its release from blood cells since their taurine concentration increased by 70% both in HC [429 (77) to 680 (82) μM; P=0.003] and in DC [451 (57) to 731 (34) μM; P<0.001]. The lack of correlation between plasma volume modification and the mass ratio of taurine would exclude a major role for taurine exchange in plasma volume regulation. Sodium (R=0.967, P<0.001), chloride (R=0.917, P<0.001) and osmolality (R=0.924, P<0.001) seem to be the main regulators of plasma volume changes during exercise. In conclusion, changes in the plasma taurine content during endurance exercise is related to an osmoregulatory process, but this alone does not control plasma volume changes. Electronic Publication     

The danger of an inadequate water intake during prolonged exercise

Summary To prevent thermal injuries during distance running, the American College of Sports Medicine proposes that between 0.83 and 1.65 l of water should be ingested each hour during prolonged exercise. Yet such high rates of fluid intake have been reported to cause water intoxication. To establish the freely-chosen rates of fluid intake during prolonged competitive exercise, we measured fluid intake during, body weight before and after, and rectal temperature after competition in a total of 102 runners and 91 canoeists competing in events lasting from 170–340 min. Fluid intakes during competition ranged from 0.29–0.62 l · h^–1; rates of water loss ranged from 0.69–1.27 l · h^–1 in the runners; values were lower in the canoeists. Mean post-race rectal temperatures ranged from 38.0–39.0° C. There was no relationship between the degree of dehydration and post-race rectal temperature. We conclude that hyperthermia is uncommon in prolonged competitive events held in mild environmental conditions, and that exercise intensity, not the level of dehydration, is probably the most important factor determining the postexercise rectal temperature. During prolonged exercise in mild environmental conditions, a fluid intake of 0.5 l · h^–1 will prevent significant dehydration in the majority of athletes.     

Left ventricular function in endurance runners during exercise

Left ventricular function in elite runners and controls was compared by means of nuclear angiocardiography. Fifteen middle- or long-distance runners and a control group of 10 sedentary to moderately physically active subjects were studied at rest and during semi-sitting incremental exercise. Ejection fraction was higher in the runners than the controls both at rest and during exercise. At the transition from rest to exercise left ventricular end-diastolic volume initially increased similarly in runners and controls by an average of 14 and 12%, respectively, with an increase in stroke volume by ≈25 and 23%. The parallel increase in stroke volume and left ventricular end-diastolic volume could a least partly be because of the 10 –Starling mechanism. With increasing workloads, left ventricular end-diastolic volume and ejection fraction remained fairly constant, resulting in an unchanged stroke volume from the lowest to the highest exercise intensity. This was in the runners?accomplished by a 41% increase in peak filling rate and a 38% increase in peak emptying rate with similar changes observed in the controls. This has to be due to increased myocardial contractility paralleling the systolic shortening with increasing heart rate. We conclude that endurance-trained athletes have a better systolic function expressed as higher ejection fraction both at rest and during exercise than untrained subjects reflecting an enhanced myocardial contractility contributing to the maintenance of a large stroke volume during exercise. The regulatory mechanisms however, appear to be similar for athletes and healthy controls.     

An acute oral dose of caffeine does not alter glucose kinetics during prolonged dynamic exercise in trained endurance athletes

This study investigated the possible influence of oral caffeine administration on endogenous glucose production and energy substrate metabolism during prolonged endurance exercise. Twelve trained endurance athletes [seven male, five female; peak oxygen consumption ( ) = 65.5 ml·kg^–1·min^–1] performed 60 min of cycle ergometry at 65% twice, once after oral caffeine administration (6 mg·kg^–1) (CAF) and once following consumption of a placebo (PLA). CAF and PLA were administered in a randomized double-blind manner 75 min prior to exercise. Plasma glucose kinetics were determined with a primed-continuous infusion of [6,6-²H]glucose. No differences in oxygen consumption ( ), and carbon dioxide production ( ) were observed between CAF and PLA, at rest or during exercise. Blood glucose concentrations were similar between the two conditions at rest and also during exercise. Exercise did lead to an increase in serum free fatty acid (FFA) concentrations for both conditions; however, no differences were observed between CAF and PLA. Both the plasma glucose rate of appearance ( ) and disappearance ( ) increased at the onset of exercise (P<0.05), but were not affected by CAF, as compared to PLA. CAF did lead to a higher plasma lactate concentration during exercise (P<0.05). It was concluded that an acute oral dose of caffeine does not influence plasma glucose kinetics or energy substrate oxidation during prolonged exercise in trained endurance athletes. However, CAF did lead to elevated plasma lactate concentrations. The exact mechanism of the increase in plasma lactate concentrations remains to be determined. Electronic Publication     

The influence of the initial state of hydration on endocrine responses to exercise in the heat

Summary This study examines the effect of the initial state of hydration on hormone responses to prolonged exercise in the heat. Five subjects at two initial hydration levels (hypohydrated and hyperhydrated) were exposed to a 36°C environment for 3 h of intermittent exercise. During exercise, the subjects were either fluid-deprived, or rehydrated with water or an isotonic electrolyte sucrose solution (ISO). Both the stress hormones, adrenocorticotropic hormone and cortisol, and the main fluid regulatory hormones, aldosterone, renin activity (PRA) and arginine vasopressin (AVP), were measured in blood samples taken every hour. Prior hyperhydration significantly reduced initial AVP, aldosterone and PRA levels. However, except for AVP, which responded to exercise significantly less in previously hyperhydrated subjects (p<0.05), the initial hydration state did not influence the subsequent vascular and hormonal responses when the subjects were fluid-deprived while exercising. Concurrent rehydration, either with water or with ISO, reduced or even abolished the hormonal responses. There were no significant differences according to the initial hydration state, except for PRA responses, which were significantly lower (p<0.01) in previously hyperhydrated subjects who also received water during exercise. These results indicate that prior hydration levels influence only slightly the hormonal responses to prolonged exercise in the heat. Progressive rehydration during exercise, especially when extra electrolytes are given, is more efficient in maintaining plasma volume and osmolarity and in reducing the hormonal responses.     

Sex differences in endurance capacity and metabolic response to prolonged,heavy exercise

Summary In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n=6) and men (n=7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes ( ). The groups were matched for age and physical activity habits. At 80% the women performed significantly longer (P<0.05), 53.8±12.7 min vs 36.8±12.2 min, respectively (means ± SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90% the endurance times were similar for men and women, 21.2±10.3 min and 22.0±5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol·l^–1) than those obtained at , suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.     

Immunological relationship between anionic antimicrobial proteins from caries-free individuals and known salivary antimicrobial factors

We examined whether the anionic inhibitory proteins identified in mixed saliva from certain caries-free individuals are fragments or degradation products of recognized salivary antimicrobial factors. In the experiments reported here, the anionic inhibitory proteins did not produce precipitin reactions with antisera to any of the established salivary antimicrobial factors examined. Additionally, native, heat-treated, or urea-denatured known salivary antimicrobial factors did not react with the antiserum to the anionic inhibitory proteins. However, the antiserum to the anionic inhibitory proteins was found to be reactive with a protein concentrate from mixed saliva or from separate submandibular and parotid secretions from a number of different donors, as well as with a purified protein fraction containing the homologous anionic inhibitory proteins. These findings suggest that the anionic inhibitory proteins represent intact and unique salivary proteins and not the degradation fragments of salivary antimicrobial protein factors within the oral environment.