Oxidative Stress After Three Different Intensities of Running - CiteSeerX

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Oxidative Stress After Three Different Intensities of Running Cláudia Dornelles Schneider1, Jaqueline Barp2, Jerri Luiz Ribeiro1, Adriane Belló-Klein2, and Alvaro Reischak Oliveira1

Catalogue Data Schneider, C.D.; Barp, J.; Ribeiro, J.L.; Belló-Klein, A.; and Oliveira, A.R. (2005). Oxidative stress after three different intensities of running. Can. J. Appl. Physiol. 30(6): 723734. © 2005 Canadian Society for Exercise Physiology. Key words: free radicals, lipid peroxidation, erythrocytes, antioxidant enzymes, exercise Mots-clés: radicaux libres, peroxydation lipidique, érythrocytes, enzymes antioxydantes, exercice physique

Abstract/Résumé In 8 trained subjects (T) and 9 untrained subjects (UT), lipid peroxidation (LPO), total antioxidant capacity (TRAP), superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities were measured in the blood before and after three different intensities of exercise on the treadmill, determined from ventilatory threshold and maximal oxygen uptake data, obtained from a maximal aerobic power test. In plasma, LPO decreased from 3589 ± 193 to 3274 ± 223 cps·mg Hb–1 (p < 0.05), and TRAP increased from 304 ± 45 to 384 ± 57 µmol·L–1 trolox (p < 0.05) after high intensity exercise in T. GPx activity increased in the T group as compared to the UT group, after exercise in moderate (25.90 ± 3.79 to 15.05 ± 3.23 nM·min–1·mg protein–1) and high (21.75 ± 4.91 to 12.1 ± 2.46 nM·min–1·mg protein–1) intensities (p < 0.05). Superoxide dismutase activity increased after exercise at low (8.35 ± 0.85 to 9.23 ± 1.03 U SOD·mg protein–1) and moderate (8.89 ± 0.98 to 10.44 ± 0.86 U SOD·mg protein–1) intensity in UT (p < 0.05). There were no changes in catalase activity. These findings indicate that exercise in this model did not increase lipid peroxidation, probably because of the alterations in TRAP and enzymatic antioxidants.

1Lab.

de Pesquisa do Exercício, Escola de Educação Física, Univ. Federal do Rio Grande do Sul, Rua Felizardo 750, CEP 90690-200, Porto Alegre, RS, Brazil; 2Lab. de Espécies Ativas de Oxigênio, Dept. de Fisiologia, Univ. Federal do Rio Grande do Sul, Rua Sarmento Leite 500, CEP 90050-170 Porto Alegre, RS, Brazil. 723

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Huit sujets entraînés (T) et 9 sujets non entraînés (UT) ont participé à trois . épreuves sur tapis roulant et d’intensité différente établie d’après le seuil ventilatoire et le VO2max mesurés au cours d’un test de puissance aérobie maximale. Avant et après chacun des efforts, on a analysé la peroxydation lipidique (LPO), la capacité antioxydante totale (TRAP), et les activités de la superoxyde dismutase (SOD), de la catalase, et de la glutathion peroxydase (GPx). La LPO plasmatique diminua de 3589 ± 193 à 3274 ± 223 cps·mg Hb–1 (p < 0,05), et la TRAP augmenta de 304 ± 45 à 384 ± 57 µmol·L–1 de trolox (p < 0,05) après l’exercice de forte intensité dans le groupe T. Comparativement au groupe UT, l’activité de la GPx dans le groupe T fut plus élevée (p < 0,05) après l’exercice d’intensité modérée (25,90 ± 3,79 comparativement à 15,05 ± 3,23 nM·min–1·mg de protéine–1) et d’intensité élevée (21,75 ± 4,91 comparativement à 12,1 ± 2,46 nM·min–1·mg de protéine–1). Dans le groupe UT (p < 0,05), l’activité de la SOD passa de 8,35 ± 0,85 à 9,23 ± 1,03 U SOD·mg de protéine–1 à la suite de l’exercice de faible intensité et passa de 8,89 ± 0,98 à 10,44 ± 0,86 U SOD·mg de protéine–1 à la suite de l’exercice d’intensité modérée. On n’observa aucune variation de l’activité de la catalase. D’après les observations dans ce contexte expérimental, l’exercice physique n’augmente pas la peroxydation lipidique, et cela est probablement dû à la modification de la TRAP et de l’activité des enzymes antioxydantes.

Introduction Physical exercise leads to increased oxygen consumption, which in turn generates free radicals (Heunks et al., 1999). If these free radicals overwhelm the antioxidant system, we have oxidative stress affecting lipids, proteins, and nucleic acids (Sies, 1986). The antioxidant defense system includes enzymes such as superoxide dismutase, glutathione peroxidase, and catalase, and other substances found in plasma (uric acid, vitamins, etc.), which in a cooperating system provide protection (Yu, 1994). It has been postulated that oxidative stress occurs during high intensity exercise (Ebbeling and Clarkson, 1989; Lovlin et al., 1987). However, it is not clear at which intensity it occurs, and whether different . levels of fitness have an influence on oxidative stress. Maximal oxygen uptake (VO2max) is considered the best cardiorespiratory endurance and fitness measurement (Wilmore and Costill, 2001). However, the capacity of prolonged exercise is only partly explained by . VO2max. Thus, another index must be used to assess athletes and healthy persons. In order to determine effort intensity more precisely for each subject, we . used the ventilatory thresholds rather than percent VO2max or maximal heart rate, in agreement with Lucía et al. (2000) and Wasserman et al. (1994). Therefore, the purpose of this study was to examine the effect of three exercise intensities based on ventilatory thresholds on blood enzyme activities, antioxidant capacity, and lipid peroxidation. We hypothesized that high intensities of exercise would induce oxidative stress, and that responses would be different in trained triathletes as compared with nonathletes.

Material and Methods SUBJECTS

Seventeen healthy young men volunteered for the study and were assigned to groups using a 2 × 3 × 2 factorial design according to training level (trained or untrained),

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exercise intensity (low, moderate, or high intensity) and exercise time (before or after exercise). This method was chosen in order to build a robust process, with minimum variability of external sources. The subjects were divided in two groups: 8 triathletes in the trained group (T) and 9 physical education students in the untrained group (UT). Age, height, weight, and % fat were, respectively for T and UT groups, 27 ± 1 and 24 ± 1 years; 175 ± 2 and 177 ± 3 cm; 72 ± 2 and 73 ± 4 kg; 8 ± 0.5 and 12 ± 1%. As expected, % fat was smaller in T (p < 0.05). The volume of training was assessed by the subject’s weekly schedule of training. All subjects were informed about the possible risks and discomforts involved in the study, and all signed a consent form. This study was approved by the ethics committee of the Federal University of Rio Grande do Sul (Protocol No. 200024). EXPERIMENTAL DESIGN

All tests were undertaken in the morning. Triathletes maintained their training programs during the study, and all subjects were asked to maintain their normal diet in this period. Individuals who had never undergone a maximal exercise test were submitted to one prior to the study so as to familiarize themselves with the treadmill. Each subject underwent 4 exercise tests on an electronic treadmill. In the first test . a progressive incremental protocol was used to determine the individual’s VO2max, aerobic threshold (AeT), and anaerobic threshold (AnT). The other three exercise tests were performed in random order and were designed so that, after a 10-min .adaptation period, subjects were able to maintain a steadystate oxygen uptake (VO2) corresponding. to that at 10% below AeT, 10% below AnT, and the average between AnT and VO2max, for 30 min. Respectively, these were called VT1, VT2, and AnM intensities. This protocol was established to guarantee that 3 different exercise intensities would be used: low (VT1), intermediate (VT2), and high (AnM). A standard pretest meal composed of 1 g carbohydrate per kg of body mass (Carb up, Probiótica, São Paulo, Brazil) was eaten 1 hr before the submaximal tests. Prior to the submaximal tests, blood samples were taken and cooled. The subjects breathed through a facemask connected to a pneumotachograph and a gas analyzer (MGC CPX/D, Medical Graphics Corp., St. Paul, MN). The ventilatory variables were calculated on-line using a microcomputer (software Breeze Ex v.3.06 supplied by Medical Graphics). ECGs were recorded continuously for the determination of heart rate. Maximal Exercise Test. The initial velocity was 5 km·h–1 for both groups, then work rate was increased by 0.5 km·h–1 every 20 s (T) and by 0.5 km·h–1 every 30 s (UT) until the exercisers were unable to run any longer and asked to stop. An incremental test with ramp protocol was chosen to allow for better identification of ventilatory threshold (VT) (Lucía et al., 2000). The first VT (AeT) was . determined by a computerized analysis of the regression equation between V O2 and . VCO2, known as V-slope (Beaver et al., 1986). The second VT (AnT) was determined using the criterion of increase in ventilatory equivalent for oxygen and ventilatory equivalent for carbon dioxide, with a concomitant decrease in end tidal pressure (Ribeiro et al., 1986). The thresholds were expressed as the corresponding . . VO2 which was determined from a linear regression equation relating time and VO2.

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Submaximal Tests. The intensity of exercise for each test day was established based on the oxygen uptake of the previously established thresholds. The subjects exercised at progressively higher intensities until they reached the target . VO2 according to the protocol .by Ribeiro et al. (1986). This protocol allowed all subjects to attain steady-state VO2 at the required level by 10 minutes and, when necessary, the velocity of the treadmill was adjusted during the test to maintain . VO2 next to the level required. Subjects were encouraged to exercise for 40 min in the VT1 and VT2 tests and for as long as they could tolerate in the AnM test. Blood Analysis. Blood samples were taken with the subjects seated, within 15 min before exercise and immediately after exercise by venous puncture of an antecubital vein. Blood samples of 7 mL were drawn into a tube with 100 µL EDTA 10% for hemoglobin (Hb), lipid peroxidation, TRAP, superoxide dismutase (SOD), catalase (CAT), and GPx analysis. After collection, samples were centrifuged for 5 min at 1,000 g. Plasma was stored at –70 °C for further analysis of TRAP. Erythrocytes were washed and centrifuged three times with the same volume of saline solution. Then 75 µL of erythrocytes were diluted in 500 µL of saline solution for LPO and Hb analysis. Both measurements were made on the same day of collection. Remaining erythrocytes were prepared and stored at –70 °C for protein and antioxidant enzyme analysis. AO enzymes were measured in red blood cells. SOD Activity. Superoxide dismutase activity was determined by the inhibition rate of pyrogallol auto-oxidation at 420 nm. This activity was determined from a standard curve of commercially available SOD (percentage inhibition of pyrogallol auto-oxidation). The reaction medium consisted of 50 mmol·L–1 tris buffer (pH 8.2), 24 mmol·L–1 pyrogallol, and 30 µmol·L–1 catalase. The results were expressed as U SOD·mg protein–1 (Marklund, 1985). GPx Activity. Glutathione peroxidase activity was measured by following NADPH oxidation at 340 nm. The reaction medium consisted of 143 mmol·L–1 phosphate buffer (pH 7.5), 1 mmol·L–1 sodium azide, 0.5 mmol·L–1 tert butyl hydroperoxide, 0.25 U·mL–1 glutathione reductase, 0.24 mmol·L–1 NADPH, and 5 mmol·L–1 reduced glutathione. The results were expressed as nmol·L–1·min–1·mg protein–1 (Flohé and Gunzler, 1984). CAT Activity. Catalase activity was measured by following the decrease in absorption at 240 nm. The reaction medium consisted of 50 mmol·L–1 phosphate buffer (pH 7.4) and 0.3 mol·L–1 hydrogen peroxide. The results were expressed as nmol·L–1·mg protein–1 (Boveris and Chance, 1973). Lipid Peroxidation. Lipid peroxidation was measured in erythrocytes using 400 mmol·L–1 tert butyl hydroperoxide initiated chemoluminescence. The light is emitted from the reaction between tert butyl hydroperoxide and lipids, and is measured in a liquid scintillation counter, adapted to count light emission using a tritium channel (LKB Rack Beta Liquid Scintillation Spectrometer, model 1215, LKB-Produkter AB, Bromma, Sweden). The reaction medium consisted of 120 mmol·L–1 KCl and 30 mmol·L–1 phosphate buffer (pH 7.4). The results were expressed as cps·mg Hb–1 (Gonzalez-Flecha et al., 1991; Llesuy et al., 1990). TRAP. Total antioxidant capacity was measured in plasma using 320 µmol·L–1 trolox as standard antioxidant. The reaction medium consisted of 20

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mmol·L–1 AZO, 50 mmol·L–1 phosphate buffer (pH 7.4), and 5.6 mmol·L–1 luminol. The results were expressed as µmol·L–1 trolox (Lissi et al., 1995). Protein. Protein was measured using the method of Lowry et al. (1951). STATISTICS

Descriptive data are presented as mean ± standard error of mean (± SEM). Threeway ANOVA was used to identify the existence of main effects of independent variables, with Student-Newman-Keuls post hoc. T-tests were used to evaluate differences between groups related to antioxidant parameters. Significance was accepted at the p < 0.05 level.

Results . VO2max averaged 56 ± 1 ml·kg–1·min–1 (T) and 43 ± 11 ml·kg–1·min–1 (UT), and week training volume averaged 19 ± 1.0 h (T) and 2.5 ± 0.7 h (UT). Both results differed significantly between groups. The steady-state oxygen consumption was maintained after 10 min of exercise in the submaximal tests at the target levels, as determined in the maximal tests. All subjects were able to complete 40 min of exercise at low and moderate intensities. During the high intensities, T stopped after 21.7 ± 2.1 min and UT stopped after 28 ± 3.9 min of exercise. OXIDANT AND ANTIOXIDANT PARAMETERS

There was a main effect of exercise on TRAP, which increased following exercise, and a main effect of fitness on GPx activity which was greater in trained individuals. Data on lipid peroxidation (LPO), total antioxidant capacity (TRAP), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) for both groups are presented in Tables 1 and 2. There was a decrease in lipid peroxidation after exercise in T at high intensity (3589 ± 193 to 3274 ± 223 cps·mg Hb–1, p < 0.05). No changes were observed at low and moderate intensities in T, nor at any intensity in UT. Furthermore, when the groups were compared, LPO did not change at any intensity. There was an increase in total antioxidant capacity after exercise in T at high intensity (304 ± 45 to 384 ± 58 µmol·L–1 trolox, p < 0.05), as well as in UT at low (334 ± 23 to 388 ± 27 µmol·L–1 trolox, p < 0.05) and high (307 ± 17 to 348 ± 16 µmol·L–1 trolox, p < 0.05) intensities. No changes in TRAP were observed when comparing groups at all intensities. In UT the superoxide dismutase activity was increased after exercise at low (8.35 ± 0.85 to 9.23 ± 1.03 U SOD·mg protein–1, p < 0.05) and moderate (8.89 ± 0.98 to 10.44 ± 0.86 U SOD·mg protein–1, p < 0.05) intensities. At high intensities no changes were observed. The T group did not show any difference after exercise at any intensity. No changes in SOD activity were observed when comparing groups at all intensities. Catalase activity was unchanged in all circumstances, including inter- and intragroup analysis at all intensities. No differences were found in glutathione peroxidase activity after exercise in either group. But comparisons between groups showed higher GPx activity after exercise in T as compared to UT, at moderate (25.90 ± 3.79 to 15.05 ± 3.23

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Table 1 Lipid Peroxidation and TRAP (M ± SEM) in Both Groups in the 3 Exercise Intensities Trained Exercise Intensity Low Before exercise After exercise Moderate Before exercise After exercise High Before exercise After exercise

Untrained

LPO

TRAP

LPO

TRAP

4127 ± 183 4420 ± 197

307 ± 234 357 ± 19

3535 ± 240 3926 ± 368

334 ± 23 388 ± 27*

3824 ± 214 3903 ± 260

352 ± 27 373 ± 50

3686 ± 318 3615 ± 339

407 ± 33 390 ± 29

3589 ± 193 3274 ± 223*

304 ± 45 384 ± 57*

3793 ± 269 4049 ± 458

306 ± 17 348 ± 16*

Note: LPO = lipid peroxidation (cps·mg Hb–1); TRAP = total antioxidant capacity (µmol·L–1 Trolox). * Significant difference between before and after, p < 0.05.

nM·min–1·mg protein–1) and high (21.75 ± 4.91 to 12.1 ± 2.46 nM·min–1·mg protein–1) intensities (p < 0.05).

Discussion An interesting feature . of this study was the use of the aerobic and anaerobic thresholds rather than % VO2max as a way to prescribe exercise intensity. The pretest meal had an antioxidant capacity of 429 µmol × L–1 trolox in a 10% carbohydrate concentration. All subjects consumed the pretest meal; therefore, biochemical measurements were affected equally in all subjects. According to McAnulty et al. (2003), carbohydrate supplementation (1 L·h–1, 6% solution) would attenuate elevations in oxidative stress markers and increase or maintain plasma antioxidant capacity during exercise of long duration. We found a reduction in lipid peroxidation after exercise of high intensity in T. Oztasan et al. (2004) did not find changes in LPO following exhaustive exercise in the erythrocytes of trained rats. They suggested that the beneficial effects of the endurance training on exercise-induced oxidative stress were partly camouflaged because of the exhaustion model of the study; i.e., if the exercise protocol were performed for a fixed time rather than to exhaustion, the protective effects of training would have been observed. While our results are in agreement with Subudhi et al. (2001), they are opposed to other data in which high intensities of exercise increase LPO (Ebbeling and Clarkson, 1989; Lovlin et al., 1987). The fact that TRAP was increased at high intensity suggests that physiological stress at this level could result in the release of antioxidant (AO) into plasma to

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Table 2 Antioxidant Enzyme Activity (M ± SEM) in Both Groups in the 3 Exercise Intensities

Exercise Intensity Low Before exercise After exercise Moderate Before exercise After exercise High Before exercise After exercise

SOD

Trained CAT

GPx

SOD

Untrained CAT

GPx

8.84 ±1.04 9.18 ±1.02

0.38 ±0.05 0.36 ±0.05

24.2 ±7.5 18.5 ±3.8

8.35 ±0.85 9.23 ±1.03*

0.39 ±0.03 0.42 ±0.04

14.7 ±4.8 17.0 ±3.7

8.81 ±0.70 9.63 ±1.01

0.33 ±0.02 0.37 ±0.03

24.7 ±5.3 25.9 ±3.7#

8.89 ±0.98 10.44 ±0.86*

0.37 ±0.04 0.38 ±0.03

22.0 ±5.0 15.0 ±3.2

7.98 ±1.04 9.30 ±1.42

0.32 ±0.03 0.36 ±0.05

19.1 ±4.6 21.7 ±4.9#

8.98 ±0.54 10.43 ±1.06

0.37 ±0.04 0.34 ±0.04

11.3 ±2.0 12.1 ±2.4

Note: SOD = superoxide dismutase (U SOD·mg prot–1); CAT = catalase (nmol·L–1·prot–1); GPx = glutathione peroxidase (nmol·L–1·min–1·mg prot–1). Significant difference, p < 0.05: * between before and after; # between trained and untrained.

protect against reactive oxygen species, as reported by Child et al. (1998). Between AO, uric acid helps to suppress LPO in erythrocytes (Ames et al., 1981) and confers potentially important free-radical-scavenging effects in vivo (Waring et al., 2003). Child et al. (1998) found an increase in LPO after a half-marathon of 87 . min duration and intensity of 77.1% VO2 peak. This intensity was close to our moderate intensity in the T group, but the duration of exercise was 40 min. It is possible that the exercise in our study did not last long enough to cause an imbalance in pro- and antioxidant systems, and thus did not cause oxidative stress. Our study did not demonstrate LPO changes in the UT group, which may suggest that some compensatory changes could have happened in the AO system. In support of this hypothesis, we found increased SOD activity at low and moderate intensities and increased TRAP at low and high intensities. Moreover, the techniques employed in the present study, as well as in the one by Quindry et al. (2003), were not sensitive enough to detect oxidative stress at submaximal intensities. New methods, such as the copper-induced lipoprotein oxidation measurement used by Cazzola et al. (2003), could be employed.

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There was a main effect of exercise increasing TRAP. More specifically, there was an increment of TRAP at high intensity in T, and at low and high intensities in UT. Child et al. (1998) found an increase in AO capacity of trained subjects after a half-marathon. The intensity was similar to the one in our moderate test, but the duration was more than double (87 × 40 min) and probably results in release and consumption of AO into plasma to provide a metabolic balance at this intensity. With regard to the rise in TRAP at high intensity, it is possible that great effort to run at the highest velocity with high oxygen uptake may have led to greater release of antioxidants. Possibly such antioxidants were not consumed due to the short duration of exercise (21.7 ± 2.1 min). Cazzola et al. (2003) found that nonenzymatic AO such as uric acid, ascorbic acid, and α-tocopherol increased in the plasma of athletes as compared to controls. Mastaloudis et al. (2001) found that another kind of exhausting exercise like running 50 km led to an increased concentration of uric acid in plasma. And by studying untrained people, Waring et al. (2003) found that high concentrations of circulating uric acid can prevent oxidative stress in vivo during intense physical exercise. We did not find differences in TRAP when comparing the groups. In marathon runners, Bergholm et al. (1999) found a lower concentration of uric acid than in untrained subjects. The T group had a tendency for increased SOD activity, but it was not significant. In a study by Marzatico et al. (1997), SOD activity in erythrocytes increased after a half-marathon, just as reported by Ozlasan et al. (2004), in which SOD activity was increased in trained rats submitted to strenuous exercise. On the other hand, Subudhi et al. (2001) found a decrease in SOD activity in Alpine skiers after 10 weeks of training. There is evidence .relating aerobic training to increasd SOD activity, such as a correlation between VO2max and SOD activity in human vastus lateralis. This adaptation seems more important in highly oxidative muscles (Powers et al., 1999). The only difference found in our study was an increase in SOD activity only in the UT group after low and moderate intensity exercise. No changes were found at high intensity, unlike the results obtained by Vesovic et al. (2002), which reflect the presence of oxidative stress in erythrocytes of control subjects following strenuous exercise. Perhaps superoxide radical production was responsible for this increase. On the other hand, the study by Oztasan et al. (2004) demonstrated decreased SOD activity in erythrocytes in sedentary rats after strenuous exercise. Comparing groups at all intensities, no significant difference was found. This is in accordance with Selamoglu et al. (2000), who compared long-distance runners and untrained subjects. In contrast, other studies found an increase in SOD activity in the blood of trained individuals (Balakrishnan and Anuradha, 1998; Cazzola et al., 2003; Marzatico et al., 1997; Metin et al., 2003) and in the hearts of trained rats (BellóKlein et al., 2000) as compared to untrained counterparts. This result could be attributed to enzyme activation in response to an augmented production of ROS. Studies involving exercise show contradictory results. At any rate, SOD is an enzyme that is responsive to exercise and deserves further research (Subudhi et al., 2001). Our findings of CAT activity in erythrocytes did not show significant differences between groups or between intensities of exercise. Results in the literature

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agree with our findings. Balakrishnan and Anuradha (1998) did not find changes in CAT activity comparing trained and untrained subjects, and Belló-Klein et al. (2000) did not find changes. in CAT activity when comparing the hearts of rats trained for 4 weeks at 50% VO2max and their controls. By contrast, in a study by Marzatico et al. (1997), long-distance runners and sprinters demonstrated higher basal levels of CAT as compared to controls. Inal et al. (2001) found that in aerobic and anaerobic swimmers, CAT activity was increased following exercise. It is interesting to note that several studies have assessed the human antioxidant defense system measuring the glutathione system, GSH/GSSG (Dufaux et al., 1997; Itoh et al., 1998), glutathione peroxidase (Ramires and Ji, 2001) and superoxide dismutase (Subudhi et al., 2001), and total antioxidant capacity (Venditti and Di Meo, 1997; White et al., 2001), but CAT activity was not measured. Maybe our protocol did not cause an increase in hydrogen peroxide but in another organic peroxide, since GPx activity was enhanced. For GPx, there was a main effect of fitness showing that triathletes had higher GPx activity than untrained subjects. The GPx antioxidant potential in erythrocytes (Tessier et al., 1995) and in vastus lateralis muscle (Hellstein et al., 1996) may have. developed with endurance training, and there is a positive correlation between VO2max and GPx activity in erythrocytes (Margaritis et al., 1997). Our GPx results were significantly higher after moderate and high intensity exercise in T as compared with UT, and they are in accord with Inal et al. (2001), who found a rise in erythrocyte GPx activity in swimmers after aerobic and anaerobic exercise. However, these results could be influenced by gender. The presence of 17β estradiol in females can increase GPx activity (Kanaley and Ji, 1991). Several works show increased GPx activity both in human and animal blood and tissues. Our data corroborate this finding. Training probably promotes a chronic increase in the formation of lipid or nonlipid hydroperoxides, such as H2O2, inducing an increase in GPx activity.

Conclusion In summary, our data indicate that total antioxidant capacity was increased after exercise, and that GPx activity was higher in triathletes than in untrained subjects. CAT activity showed no changes, indicating that the ROS involved in this model were probably organic peroxides which were scavenged by GPx. On the other hand, we can speculate that this model of exercise could raise plasma uric acid, vitamins, and other AOs, which would increase serum antioxidant capacity and reduce exercise-induced oxidative stress in this population. Acknowledgments This research was supported by CAPES, CNPq, and the Federal Ministry of Sports of Brazil.

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