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Original Research

Increased Oxidative Stress Blood Markers in Well-Trained Rowers Following Two Thousand-Meter Rowing Ergometer Race

Kyparos, Antonios1; Vrabas, Ioannis S2; Nikolaidis, Michalis G1,3; Riganas, Christos S2; Kouretas, Dimitrios1

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Journal of Strength and Conditioning Research: August 2009 - Volume 23 - Issue 5 - p 1418-1426
doi: 10.1519/JSC.0b013e3181a3cb97
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Abstract

Introduction

The generation of reactive oxygen and nitrogen species (RONS) is a physiological process that occurs as a consequence of normal cellular metabolism. However, the overproduction of RONS may be harmful to the cell oxidizing basic cell structures (such as lipids, proteins, and DNA), a process known as oxidative stress. To cope with oxidative stress, which can be further defined as the imbalance between pro-oxidant and antioxidant molecules in favor of the former, the human body employs a range of defense antioxidant mechanisms, including enzymatic and nonenzymatic antioxidants (27,38).

Acute intensive aerobic and anaerobic exercise induces oxidative stress, yet it also affects the levels of enzymatic and nonenzymatic antioxidant molecules (reviewed in (4,14,49)). Both these types of exercise increase antioxidant enzyme activity, as an immediate adapting response to the scavenging requirements imposed by RONS production. However, it seems that the upregulation of antioxidant enzyme activity is not proportional to RONS production. Similarly, both aerobic and anaerobic training are associated with prolonged adaptive response to RONS generation. With respect to endurance training, it is not clear as yet whether the reduction in oxidative stress is the result of a decreased RONS production during exercise or an increased antioxidant system efficiency or both, whereas in anaerobic training, an accumulated period of intensive exercise could in fact cause increased oxidative stress (4,14,49).

The physiological requirements of competition-level rowing are very demanding (19,34) involving maintenance of high power mostly produced from aerobic metabolism (18,35,36,46). Moreover, unlike other endurance-type events, in which a steady effort is maintained throughout the greatest portion of the race, competitive rowing appears to elicit energy production in a rather inefficient approach due to the unusual pattern elite oarsmen use in competition. More specifically, in a typical 6-minute rowing race, the initial brief (of about 1 minute) anaerobic metabolism-depended vigorous sprint is followed by a longer (of about 4 minutes) extremely high aerobic steady state and then over the last minute by an “all-out” sprint to the finish (19,20,22). This unique metabolically diverse race pattern is one of the reasons that physiology of rowing has attracted exercise scientists' research attention.

An instrument commonly used for evaluating rowing performance in the laboratory and is also internationally accepted as the standard measuring tool in rowing testing is the rowing ergometer (8,19,24). The use of the rowing ergometer test to assess rower's physical performance was first introduced in 1971 by Hagerman and Lee (25). As the technology advanced, this very first fixed-resistance mechanical rowing ergometer (as described in (22,36)) has been later substituted with more contemporary variable-resistance devices (e.g., Concept II ergometer). The 2,000-m rowing ergometer maximal performance is one of the most extensively used protocols for evaluating rower's physical capacity because it resembles the conditions of the actual competition in terms of action, duration, and intensity (19,23,32). Moreover, the 2,000-m rowing test has high reliability in determining performance in well-trained rowers; thus, it can be a useful tool for tracking potential changes in athletic performance when administered during the competition season (26,42).

Studies examining oxidative stress in response to competitive rowing are scarce. The 2 relevant studies found in the literature have looked into the effect of antioxidant supplementation on pro-oxidant and antioxidant equilibrium by determining selective blood oxidative stress markers in well-trained rowers who were studied before (45) or during (50) the competitive period of training. To further expand the knowledge on this topic, more research is required by examining additional and frequently used oxidative stress markers studied in a different training period. Thus, the present study aimed at investigating oxidative stress in response to a standard 2,000-m rowing race simulation test in highly trained rowers during the preseason preparatory training period.

Methods

Experimental Approach to the Problem

To examine oxidative stress in response to rowing race, blood redox status indices before and immediately after a simulated 2,000-m maximal rowing ergometer performance in well-trained male rowers were assessed using a paired Student's t-test. Evaluation of selective frequently used blood oxidative stress markers was performed during the preparatory training period. In particular, the concentration of the nonenzymatic molecules reduced (GSH) and oxidized (GSSG) glutathione, the activity of catalase enzyme, total antioxidant capacity (TAC), and the concentration of thiobarbituric acid-reactive substances (TBARSs) and protein carbonyls, as markers of lipid peroxidation and protein oxidation, respectively, were determined.

Subjects

Nineteen highly trained international level rowers volunteered to participate in this study. All athletes were members of the Greek National Rowing Team, and the measurements were carried out during the preseason preparatory training period. The subjects' characteristics are presented in Table 1. A written informed consent was provided by the athletes after they were fully informed of the nature, potential risks, discomforts, and benefits involved in this investigation. All experimental procedures were performed in accordance with the policy statement of the American College of Sports Medicine on research with human subjects as published in Medicine and Science in Sports and Exercise and were approved by the Institutional Review Board.

Table 1
Table 1:
Anthropometric and physiological characteristics of the subjects (n = 19).*

Preliminary Measurements

Each athlete reported to the indoor training facility in the morning of the experiment after an overnight fast of about 10 hours and abstained from consuming alcohol and caffeine-containing beverages for 24 hours. Athletes were also instructed to avoid taking any vitamin supplements or changing their regular diet the last week before testing. Body mass was measured to the nearest 0.1 kg (Beam Balance 710; Seca, Birmingham, UK) with subjects lightly dressed and barefooted. Standing height was measured to the nearest 0.5 cm (Stadiometer 208; Seca).

Experimental Protocol

Rowers performed a simulated 2,000-m rowing race on a wind resistance-braked rowing ergometer (Concept II, Morrisville, VT). The rowers were fully familiarized with the use of this apparatus. The subjects were asked to cover the 2,000-m distance on the rowing ergometer in the least time possible (2,000-m all-out test). To simulate race conditions and enhance motivation, 2 ergometers were placed side by side so that athletes performed the test in pairs competing with each other. Rowers were instructed to compete with each other as if they participated in an actual race, and they were verbally motivated by assistants to stroke at maximal effort throughout the race. Power and stroke frequency, total freewheel revolutions, and elapsed time were delivered continuously by the computer display of the rowing ergometer. Drag factor was set at 135.

Heart rate (HR) was measured at rest and continuously monitored during testing using short-range radio telemetry (Polar Sportstester; Vantage NV, Kempele, Finland). Heart rate at the completion of the 2,000-m rowing test for each subject was recorded. Time for 2,000 m was also recorded. Blood lactate in the fifth minute of recovery was determined. A standardized 5-minute warm-up on the rowing ergometer followed by a 5-minute stretching exercise was performed by the athletes before the maximal 2,000-m rowing test. Subjects were provided with water (3 ml·kg−1 body mass) after the warm-up, as well as after completing the rowing test. During testing, the temperature and relative humidity in the indoor facility where the test was performed were kept constant at 21° C and 55%, respectively.

Blood Sample Collection and Handling

Before exercise and within 5 minutes of the completion of exercise, a venous blood sample was drawn from the left antecubital vein of the reclining subjects using standard phlebotomy procedures. A portion of blood was collected into tubes containing K2EDTA as the anticoagulant and used for the determination of hematocrit (Hct) and hemoglobin (Hb). Whole blood lysate was produced by adding 5% trichloroacetic acid to whole blood (1:1 vol/vol) collected in K2EDTA tubes, vortexed vigorously, and then centrifuged at 4,000g for 10 minutes at 4° C. The supernatant was removed and centrifuged again at 28,600g for 5 minutes at 4° C. The latter step was repeated twice. The clear supernatant was then transferred to eppendorf tubes and used for reduced (GSH) and oxidized (GSSG) glutathione determination. Another portion of blood was collected and allocated to serum separation tubes, left on ice for 20 minutes to clot, and centrifuged at 1,500g for 10 minutes at 4° C. The resultant serum was transferred to eppendorf tubes and used for the determination of TBARSs, protein carbonyls, catalase, and TAC.

Blood Lactate Concentration

Blood samples were drawn from fingertip, and the concentration of blood lactate was determined in the fifth minute of recovery by using a lactate photometer analyzer (Accusport; Boehringer, Mannheim, Germany).

Plasma Volume

Postexercise plasma volume changes were calculated on the basis of Hct and Hb using the method employed by Dill and Costill (13). Hematocrit was measured by microcentrifugation, and Hb was measured using a kit from Spinreact (Santa Coloma, Spain).

Assays

Glutathione Status

Reduced glutathione and GSSG were measured according to Reddy et al. (40) and Tietze (48), respectively. For GSH, 20 μL of whole blood lysate treated with 5% trichloroacetic acid (TCA) was mixed with 660 μL of 67 mM sodium-potassium phosphate (pH 8.0) and 330 μL of 1 mM 5,5′-dithiobis-2 nitrobenzoate (DTNB). The samples were incubated in the dark at room temperature for 45 minutes, and the absorbance was read at 412 nm. GSSG was assayed by treating 50 μL of whole blood lysate with 5% TCA and neutralized up to pH 7.0-7.5 with NaOH. One microliter of 2-vinyl pyridine was added, and the samples were incubated for 2 hours at room temperature. Five microliters of whole blood lysate treated with TCA was mixed with 600 μL of 143 mM sodium phosphate (6.3 mM EDTA, pH 7.5), 100 μL of 3 mM reduced nicotinamide adenine dinucleotide phosphate (NADPH), 100 μL of 10 mM DTNB, and 194 μL of distilled water. The samples were incubated for 10 minutes at room temperature. After the addition of 1 μL of glutathione reductase, the change in absorbance at 412 nm was read for 1 minute.

Thiobarbituric Acid-Reactive Substances

For serum TBARSs, a slightly modified assay of Keles et al. (31) was used. One hundred microliters of serum was mixed with 500 μL of 35% TCA and 500 μL of Tris-HCl (200 mM, pH 7.4) and incubated for 10 minutes at room temperature. One milliliter of 2 M Na2SO4 and 55 mM thiobarbituric acid solution was added, and the samples were incubated at 95° C for 45 minutes. The samples were cooled on ice for 5 minutes and were vortexed after adding 1 mL of 70% TCA. The samples were centrifuged at 15,000g for 3 minutes at 25° C, and the absorbance of the supernatant was read at 530 nm. A baseline shift in absorbance was taken into account by running a blank along with all samples during the measurement.

Protein Carbonyls

Serum protein carbonyls were determined based on the method of Patsoukis et al. (39). Fifty microliters of 20% TCA was added to 50 μL of serum, and this mixture was incubated in an ice bath for 15 minutes and centrifuged at 15,000g for 5 minutes at 4° C. The supernatant was discarded and 500 μL of 10 mM 2,4-dinitrophenylhydrazine (in 2.5 N HCL) for the sample, or 500 μL of 2.5 N HCL for the blank, was added in the pellet. The samples were incubated in the dark at room temperature for 1 hour, with intermittent vortexing every 15 minutes, and were centrifuged at 15,000g for 5 minutes at 4° C. The supernatant was discarded and 1 ml of 10% TCA was added, vortexed, and centrifuged at 15,000g for 5 minutes at 4° C. The supernatant was discarded and 1 mL of ethanol-ethyl acetate (1:1 vol/vol) was added, vortexed, and centrifuged at 15,000g for 5 minutes at 4° C. This washing step was repeated twice. The supernatant was discarded and 1 mL of 5 M urea (pH 2.3) was added, vortexed, and incubated at 37° C for 15 minutes. The samples were centrifuged at 15,000g for 3 minutes at 4° C, and the absorbance was read at 375 nm. Total serum protein was assayed using a Bradford reagent from Sigma-Aldrich.

Catalase

Catalase activity was determined using the method of Aebi (1). According to this protocol, 2,975 μl of 67 mM sodium-potassium phosphate (pH 7.4) was added to 20 μl of serum and the samples were incubated at 37° C for 10 minutes. Five microliters of 30% hydrogen peroxide was added to the samples, and the change in absorbance was immediately read at 240 nm for 2 minutes.

Total Antioxidant Capacity

The determination of TAC was based on the method of Janaszewska and Bartosz (29). Four hundred eighty microliters of 10 mM sodium-potassium phosphate (pH 7.4) and 500 μL of 0.1 mM 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical were added to 20 μL of serum, and the samples were incubated in the dark for 60 minutes at room temperature. The samples were centrifuged for 3 minutes at 20,000g, and the absorbance was read at 520 nm.

Each assay was performed in duplicates on the same day to minimize variation in assay conditions and within a month of the blood collection. Blood samples (serum and whole blood lysate) were stored in multiple aliquots at −80° C and thawed only once before analysis. The intra- and interassay coefficients of variation for each measurement were 4.1 and 4.5% for GSH, 6.1 and 7.3% for GSSG, 4.7 and 5.9% for TBARSs, 5.4 and 7.0% for protein carbonyls, 7.0 and 10.0% for catalase, and 3.4 and 5.4% for TAC, respectively. All reagents were purchased from Sigma-Aldrich (St. Louis, MO).

Statistical Analyses

Data were analyzed using SPSS, version 14 (SPSS, Chicago, IL), and presented as mean ± SEM. The distribution of all dependent variables was examined by the Shapiro-Wilk test and was found not to differ significantly from normal. To evaluate any differences in the blood oxidative stress markers of the subjects between pre- and postexercise, a paired Student's t-test was applied. The level of statistical significance was set at α = 0.05. To determine the meaningfulness of the effect of exercise on each dependent variable, effect sizes were calculated as the difference between post- and pre-exercise mean concentrations divided by the SD of the pre-exercise concentration. Effect sizes of 0.2, 0.6, 1.2, 2.0, and 4.0 were considered to be small, moderate, large, very large, and nearly perfect, respectively, according to a modified Cohen's scale (http://newstats.org). For comparison, the values of the original Cohen's scale are 0.2 for small, 0.5 for moderate, and 0.8 for large effects (9).

Results

The subjects' characteristics are presented in Table 1. Mean time for T2,000 m was 409.4 ± 4.0 seconds. Mean HR at 2,000 m (HR2,000 m) was 197.8 ± 1.0 b·min1. There was a significant change in Hct (40.8 ± 2.9% vs. 41.8 ± 2.7%, p < 0.0001) and Hb (14.6 ± 0.9 g·dL−1 vs. 14.7 ± 0.8 g·dL−1, p < 0.23) values before and after exercise, respectively. Postexercise plasma volume relatively to pre-exercise value was 0.975 ± 0.03. All postexercise values were corrected for plasma volume change. Postexercise blood lactate levels were 11.2 ± 0.6 mmol·L1.

Glutathione Status

Data of the oxidative stress markers examined are presented in Figures 1-3. GSH concentration remained unchanged (pre 0.52 ± 0.03 vs. post 0.50 ± 0.03 mM, p > 0.05) (range 36-78 vs. 0.29-0.79), whereas GSSG concentration was increased (pre 0.063 ± 0.01 vs. post 0.075 ± 0.01 mM, p < 0.05) (range 0.02-0.10 vs. 0.04-0.15), after the 2,000-m rowing ergometer test. As a result, GSH:GSSG ratio was significantly decreased after exercise (pre 9.9 ± 1.6 vs. post 7.1 ± 0.7, p < 0.05) (range 6.2-34.6 vs. 0.4-0.18). The effect size of exercise on GSH, GSSG, and GSH:GSSG ratio was −0.15, +0.60, and −0.39, respectively.

Figure 1
Figure 1:
Glutathione status pre (open bars) and post (solid bars) exercise. Values represent mean ±SEM (n = 19). A) GSH = reduced glutathione. B) GSSG = oxidized glutathione. C) GSH:GSSG ratio. Asterisk indicates significant difference (p < 0.05).
Figure 2
Figure 2:
A) TBARS and (B) protein carbonyl concentration pre (open bars) and post (solid bars) exercise. Values represent mean ±SEM (n = 19). TBARSs = thiobarbituric acid-reactive substances. Asterisk indicates significant difference (p < 0.0001).
Figure 3
Figure 3:
A) Catalase activity and (B) TAC concentration pre (open bars) and post (solid bars) exercise. Values represent mean ±SEM (n = 19). TAC = total antioxidant capacity. Asterisk indicates significant difference (p < 0.0001).

Thiobarbituric Acid-Reactive Substances and Protein Carbonyls

Both TBARS (pre 4.0 ± 0.5 vs. post 5.8 ± 0.5 μM) (range 1.0-8.0 vs. 3.4-11.3) and protein carbonyl (pre 0.43 ± 0.03 vs. post 0.73 ± 0.04 nmol·mg−1 protein) (range 0.22-0.66 vs. 0.46-1.07) concentration was increased (p < 0.0001) after the 2,000-m rowing ergometer performance. The effect size of exercise on TBARSs and protein carbonyls was +0.86 and +2.50, respectively.

Catalase and Total Antioxidant Capacity

Similarly, catalase activity (pre 14.0 ± 1.4 vs. post 28.7 ± 3.8 mM·min−1) (range 6.6-27.0 vs. 9.9-65.0) and TAC (pre 0.68 ± 0.01 vs. post 0.74 ± 0.01 mM [DPPH]) (range 0.60-0.76 vs. 0.63-0.85) were significantly increased (P < 0.0001) after rowing test. The effect size of exercise on catalase and TAC was +2.45 and +2.20, respectively.

Discussion

Our data demonstrate that maximal 2,000-m rowing ergometer performance increases oxidative stress in well-trained rowers, as evidenced by the significant increase in serum TBARSs, protein carbonyls, catalase activity, TAC, and whole blood lysate GSSG concentration, as well as the significant decrease in GSH:GSSG ratio.

These findings are in agreement with the results of recently published studies that examined selective blood oxidative stress markers in response to 2,000-m rowing ergometer test performed before (45) or during (50) the competitive period of training. It is noted that both above-mentioned studies used well-trained male rowers of similar-to our subjects-age, years of training, and physical capacity (the mean time for the 2,000-m test was 6.6, 6.8, and 6.8 minutes in Skarpanska-Stejnborn et al., Zembron-Lacny et al., and our study, respectively), yet our measurements were carried out during the preseason preparatory training period.

More specifically, Skarpanska-Stejnborn et al. (45) found a 7% increase in plasma TAC and a 94% increase in red blood cell lysate TBARSs immediately after the rowing test compared with 9 and 45% increase in serum TAC and TBARSs, respectively, observed in our study. Accordingly, Zembron-Lacny et al. (50) showed a 76 and 12% increase in red blood cell lysate TBARS and catalase activity, respectively, compared with 105% increase in serum catalase detected in our study. Besides, postexercise increase in plasma protein carbonyl concentration (78%) was similar to that found in our study (70%). The different percent increase in TBARS and catalase activity observed between our study and that of the 2 aforementioned studies could be attributed to the fact that we measured these markers in serum, whereas Skarpanska-Stejnborn et al. (45) and Zembron-Lacny et al. (50) estimated them in erythrocytes. Nevertheless, the changes observed in these parameters were to the same direction, suggesting increased oxidative stress.

In a recent work conducted in our laboratory, we studied oxidative stress using an exercise modality of approximately the same duration to that of the rowing ergometer test. The findings of our previous work were consistent to the ones of the present study showing that an acute 6-minute exhaustive aerobic exercise, consisting of shuttle runs toward the sidelines within the tennis singles court, significantly increased all oxidative stress blood markers currently examined (33).

The extent of oxidative damage during physical activity depends on several parameters including exercise duration and adaptation level to the particular activity. However, the intensity of the effort is recognized as the key factor to elicit oxidative stress during physical activity (4,14). The 2,000-m rowing ergometer test is a relatively short high-intensity endurance event that closely mimics the metabolic demands of the actual race, thus adequately representing the task of race rowing (18,19,22,35,46). In this regard, ergometric rowing can provide valid and reliable data for evaluating aerobic capacity (19).

Increased oxygen consumption during exercise is associated with a rise in reactive oxygen species (ROS) production probably due to the electron leakage in mitochondrial respiratory chain where oxidative phosphorylation takes place (6,10). In our study, o2 during the 2,000-m maximal rowing ergometer test has not been directly measured. Therefore, to estimate the relative contribution of aerobic and anaerobic metabolism during the task, we must rely on the data of previous studies that actually measured o2. Mickelson and Hagerman (36) found that the world-class male oarsmen during a progressive exercise test to exhaustion on a rowing ergometer were able to generate approximately 72% of the total power output at anaerobic threshold, which corresponded to 83% of o2max. The anaerobic threshold occurred between 10 and 11 minutes, whereas the o2max was reached at approximately 15 minutes. However, in the 6-minute maximal rowing test, due to the unusual pacing pattern of the race, peak o2 values were often achieved during the second to the fourth minute, rarely in the fifth minute, and never in the sixth minute of the rowing test (22).

A previous work of the same research group also showed that 70% of the mean power output in elite rowers during a 6-minute simulated rowing test was produced aerobically and the rest 30% anaerobically (22). These values seemed to be relatively proportional to those calculated (16) who reported an 80% aerobic and 20% anaerobic relative contribution during a 5-minute maximal exercise. Support to these findings was also provided by the data on the relative contribution of aerobic energy system to the total energy supply during varying periods of intensive exercise, presented by Gastin (15). In this work (15), the aerobic contribution during a 7-minute maximal trial was estimated to be around 90%, the rest coming from the anaerobic metabolism. Nevertheless, equal maximal aerobic values between rowing race simulated test and graded treadmill exercise test were reported (7,21), probably reflecting a similar amount of muscle mass engaged in each exercise modality.

Heart rate has been traditionally used as an indirect indicator of average exercise intensity as it is linearly related to o2 during exercise (12). Hagerman et al. (24) have demonstrated a very strong linear relationship between HR and o2 during both incremental rowing ergometer and cycle ergometer exercise tests in untrained men and women ranging in age from 20 to 74 years. In the rowing test, these authors reported correlation coefficients between HR and o2 as high as r = 0.989 and r = 0.971, for men and women, respectively, whereas the respective correlations in cycle ergometer exercise were r = 0.997 and r = 0.990.

In the present study, the rowers' mean HR of 198 b·min1, measured at 2,000-m rowing ergometer race, represents about 98% of the subjects' predicted maximal HR, which in turn corresponds to about 95% of their predicted maximal oxygen consumption (37,47). Similar HR values to that recorded in our subjects were also reported during an all-out 2,000-m rowing ergometer test (45,50) and associated with high values (68 ml·kg1·min1) of maximal oxygen consumption (45), indicating that maximal exercise intensity was reached. More importantly, similar maximal HR values, averaging 190-200 b·min1, were reported during simulated and actual rowing (25,28,43), suggesting that both tasks induced comparable physiological alterations.

Although increased aerobic metabolism is considered to have the prevalent role in inducing ROS production, the anaerobic component of exercise should not be underestimated, as accumulative evidence shows that anaerobic metabolism also induces significant oxidative stress (4,5,14). The production of lactic acid is a potential mediator to oxidative stress related to anaerobic exercise. It was demonstrated in vitro that acidosis triggered increased ROS formation and lipid peroxidation in brain tissue homogenates, whereas it also related to decreased tissue content of vitamin E, a known antioxidant (44). These effects are likely involving enhanced formation of the protonated form of superoxide radicals, which is highly pro-oxidant. More interestingly, a linear direct correlation between blood lactate concentration and glutathione oxidation after exhaustive exercise was observed (41), whereas antioxidant supplementation attenuated blood lactate concentration after a maximal exercise test (2).

The significant involvement of anaerobic metabolism in 2,000-m simulated rowing ergometer test, also indicative of the intensive effort exerted by the rowers, is manifested by the high levels of blood lactate following the task. Hagerman et al. (22) demonstrated that lactate peak concentration was occurred at the second minute and essentially maintained thereafter until cessation of exercise, suggesting lactate oxidation during the 6-minute rowing ergometer test. In our study, the high postexercise blood lactate values (11.2 mmol·L1) were in agreement to the peak blood lactate values reported by other investigators during a simulated rowing test (14.7, 15.4, and 14.1 mmol·L1, in studies (23,45,50), respectively).

The data of the present study coupled with those of Skarpanska-Stejnborn et al. (45) and Zembron-Lacny et al. (50) indicate that a relatively short predominantly aerobic event of maximal intensity can induce oxidative stress. This finding becomes of a relevant importance given that the subjects were highly trained rowers who performed an accustomed type of exercise specific to rowing. These findings indicate that despite the high training status of rowers employed in the present study blood oxidative stress could not be prevented.

Chronic aerobic exercise has been associated with a training-induced adaptation response against oxidative stress. The majority of studies indicate that endurance training increases antioxidant defense status and reduces ROS production, thus overall reducing postexercise oxidative stress (14). In contrast, the relatively few data about the effect of anaerobic training on such adaptation responses are controversial, failing to clearly show amelioration in oxidative stress postexercise after implementation of anaerobic training protocols (4,14). In the single study found in the literature on oxidative stress during high-intensity rowing training, chronic strenuous rowing exercise did not appear to either increase or decrease oxidative stress (11). Blood and muscle TBARSs were found to be essentially unchanged in collegiate rowers during a 4-week high-intensity rowing training, suggesting no apparent training-induced effect on oxidative stress (11).

Even though it is generally accepted that changes in certain blood biomarkers are indicative-to a degree-of alterations that take place in a particular tissue, a limitation of the present study may be considered by the fact that the oxidative stress indices measured in blood may not be safely generalized to other tissues (3). Changes in blood oxidative stress biomarkers may not be able to proportionally reflect the extent of oxidative damage that occurs in muscles. Until this issue is fully resolved, we may accept with reservation that blood oxidative stress markers adequately reflect muscle oxidative stress.

Studies have showed that antioxidant supplementation partially attenuated oxidative damage after a 2,000-m rowing ergometer race. A single high dose of vitamin E administered before 2,000-m rowing ergometer test resulted in 13, 17, and 24% reduction in erythrocyte catalase, TBARSs, and plasma protein carbonyls, respectively, in well-trained rowers (50). No difference in 2,000-m rowing performance before and after vitamin E supplementation was found.

The involvement of free radicals in physiological adaptations during exercise has been discussed by Gomez et al. (17,30). If indeed free radicals are vital for both adaptations and performance, this is to be resolved.

Practical Applications

Based on the findings of the present study, it appears that oxidative stress increases after a rowing simulation race. Competitive rowing resulted in oxidative damage of lipids and proteins. Enzymatic and nonenzymatic molecules were elevated to cope with oxidative stress, yet oxidative stress could not be deterred. The fact that the subjects employed in the present study were well trained and accustomed to the specific rowing race simulation test suggests that oxidative damage could not be prevented by the rowers' high training level. In addition, the data of this work combined with that of other studies indicate that a maximal rowing effort induces oxidative stress to the oarsmen independently of the training season. Therefore, coaches when designing the training plan or scheduling a competition need to bear in mind that an all-out rowing effort may produce oxidative stress whether it is performed in the preparatory or competition season. In this respect, if an evaluation rowing test or a major competition is to be scheduled, coaches should allow the athletes to have sufficient recovery time between the test and the last training session, particularly if this session involves intensive training work. In addition, to better simulate the metabolic conditions that occur during the actual competition, the coach could design a microcycle training program that involves equal number of races at near-maximal effort as those performed in an actual competition (i.e., heats, semifinals, final). Proper nutrition and training status might be possible factors interfering with the degree of exercise-induced oxidative stress. The present work also showed that the 2,000-m rowing performance is a suitable test to assess oxidative stress in rowers and could potentially serve as a model to study oxidative damage in sports science. In future, it would be worth noting to examine whether the response of the less-trained novice rowers to oxidative damage produced during the rowing race would be greater than that found in elite rowers. It would be also interesting to conduct studies using oarswomen to examine the potential gender-related differences in response to oxidative stress.

Acknowledgments

No external financial support for this project was received.

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Keywords:

oarsmen; reactive oxygen species; oxidative damage; maximal effort; crew

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