In sport disciplines relying on speed endurance or strength endurance, anaerobic glycolysis provides the primary energy source for muscular contractions. The total capacity of the glycolytic pathway is limited by the progressive increase of acidity within the muscles, caused by the accumulation of hydrogen ions (Verbitsky et al., 1997). The increase in acidity ultimately inhibits energy transfer and the ability of the muscles to contract, forcing the athlete to decrease the intensity of exercise (Costill et al., 1984; Harrison and Thompson, 2005; McNaughton, 1992). The naturally occurring bicarbonates are the body's first line of defense against increased acidity. When the buffering capacity within the cell is exceeded, lactate and hydrogen ions diffuse outside the cells (McNaughton, 1992). It has been reasoned that increasing the body's extracellular buffering capacity, by boosting the bicarbonate reserve, will allow hydrogen ions to leave the exercising muscles at a faster rate; consequently, more hydrogen ions and lactate can be produced before the acidity within the muscle cells reaches a limiting level (Faff, 1993; Harrison and Thompson, 2005). The benefit from sodium bicarbonate supplementation would thus be a delayed onset of fatigue during anaerobic exercise (Cairns, 2006; Hollidge-Horvat et al., 2000; Thomas et al., 2005).

Studies with bicarbonate loading have employed various exercise protocols, different doses and times of ingestion. Ergogenic effects were investigated in relation to sprint and middle distance running, rowing, swimming, cycling and different forms of strength exercises. In most of them, significant improvements in performance have been recorded (Gao et al., 1988; Goldfinch et al., 1988; McNaughton, 1990; 1999; McNaughton and Cedero, 1991; Pilegaard et al., 1999; Thomas et al., 2005). There are however studies that do not show benefits of bicarbonate ingestion on performance (Cairns, 2006; Hollidge-Horvat et al., 2000). Experiments have been conducted with different doses of sodium bicarbonate, ranging from 100 to 500 mg/kg of body mass (Horswill et al., 2004; McNaughton et al., 1999). The research literature suggests that doses below 200 mg may cause elevations in blood bicarbonate but do not improve anaerobic performance. Ingesting doses greater than 300 mg does not further increase alkalosis, thus most scientists suggest this dose (McNaughton et al., 1999). The time allowed between ingestion and exercise has also varied from 30 to 150 min in endurance exercise and may had an effect on the alkalotic state achieved prior to exercise (Horswill et al., 2004; McNaughton, 1992; McNaughton et al., 1999; Parry-Billings and MacLaren, 1986). In well trained athletes performance benefits following bicarbonate ingestion are most often observed in single bouts of anaerobic exercise, lasting from 60 to 240s however ergogenic benefits of bicarbonate ingestion were also registered in short duration repeated sprints or resistance exercises, yet during final few repetitions or in the last trials of an exercise protocol (Bishop et al., 2004).

In swimming, athletes begin intensive training between the age of 9 and 11 (Denadai et al. , 2000) and child, youth as well as adult athletes usually take part in the same training regime. Almost all studies with buffering substances have been conducted on adult athletes or untrained male and female adults (Cairns, 2006; McNaughton, 1990; McNaughton et al., 1999; Thomas et al., 2005). Since no data is available on the effects of bicarbonate ingestion in youth athletes, we decided to investigate whether the ingestion of sodium bicarbonate brought beneficial effects on buffering capacity and swim performance in youth swimmers.

Subjects
A group of eight, well trained competitive youth male swimmers took part in the experiment. All subjects were informed of the nature of the study and possible side effects, and the parents of all the subjects gave their written consent for participation. The project was approved by the Ethics Committee for Scientific Research at the Academy of Physical Education in Katowice. The evaluation of biological development of the adolescent swimmers (Tanner's scale) confirmed that all of the subjects were post puberty.

The basic physical characteristics of the subjects were: (Mean ± SD) age 15.1 ± 0.4 years, body mass 56.1 ± 1.2 kg, height 1.66 ± 0.03 m, training experience 6.6 ± 0.6 years. The research was conducted in the pre-competitive period of an annual training cycle. During this period all swimmers trained approximately 25 h per week, including 2.5 h of strength training on land. The average volume of swim training equaled 69.5 km per week.

Protocol
Each subject completed two test trials consisting of 4 x 50 m front crawl swims with a 1 min passive rest interval between each sprint. The subjects were instructed to swim as fast as possible during each 50 m swim. The two test trials were conducted in a double blind fashion on separate days, 72 hours apart at the same time of the day. One week before and during the experiment the swimmers were placed on a mixed, isocaloric diet which included 60% carbohydrate, 20% protein and 20% fat. The average caloric value of the diet was calculated from a 3 day (2 weekdays and 1 weekend day) diet diary which was analyzed by a computer program (Dieta 2, Warsaw, Poland). The subjects arrived in the laboratory in a 3 h post-absorptive state. The pre-trial meals were standardized for all athletes and consisted of carbohydrates (70%), fat (20%) and protein (10%). During the first trial, four randomly chosen swimmers were given a 500 ml solution containing 300 mg of sodium bicarbonate (NaHCO₃) per kg of body mass while the other four athletes received a placebo solution containing an equimolar dose of sodium chloride NaCl (Van Montfoort et al., 2004). The solutions were sugar free and fruit flavored. All subjects reported similar taste of the experimental and placebo treatment solution. In the second trial the order was reversed.

The fluid was ingested over a 15 min period, 90 min before the start of the test trial. All subjects were interviewed regarding gastrointestinal distractions following sodium bicarbonate ingestion. None of the participants reported serious gastrointestinal distractions. After ingesting the solution the athletes were allowed to rest quietly for 60 min prior to testing. Before the time trials the swimmers performed a specific warm-up, which also allowed to maintain the acid-base balance at an appropriate level by stimulating the buffering capacity (Beedle et al., 2007; Poprzecki et al., 2007). The warm up procedure included continuous swimming over 300 m with moderate intensity (HR= 140-150 bts·min^-1), stretching and 3 x 25m swims with high intensity. The time of the swim trials was recorded electronically, and the average swim speed in m/s was calculated.

Blood samples were drawn from the finger tip 3 times during each trial; upon arrival to the laboratory (pre ingestion), 60 min after ingestion of placebo or the bicarbonate solution (post ingestion) and during the 1^st min of recovery (post exercise). Plasma lactate (LA) concentration was determined enzymatically using commercial kits (Boehringer Diagnostika, Mannheim, Germany). Blood pH, standard bicarbonate (SB) and base excess (BE) were measured using a 168pH Blood-Gas Analyzer (Ciba-Corning, Basel, Switzerland). The intra and interassay coefficients of variation for lactate were 3.2 and 8.9% respectively.

Statistical analysis
All results are presented as mean values and standard deviations (SD). The data was analyzed using parametric statistics following confirmation of a normal distribution by repeated Kolmogorov-Smirnov tests. To evaluate the effects of sodium bicarbonate intake on swim performance and chosen biochemical variables a two-way ANOVA for repeated measures (trial, measurements over time) was used, followed by the Tukey's post hoc test for paired observations to determine the significance of differences. Statistical significance was accepted at p < 0.05.

The swimming speed of each 50 m time trial is presented in Figure 1. The results of the ANOVA (F_(2.28)=5. 63, p < 0.05) indicate a significant effect of sodium bicarbonate ingestion on swimming performance in youth athletes during the 4 x 50 m front crawl test protocol. Post hoc tests reveal a statistically significant difference in swimming speed only in the first 50m sprint (1.92 vs. 1.97 m·s^-1, p < 0.01). In trials 3 and 4 swimming speed was higher after bicarbonate ingestion, yet these differences were statistically insignificant. There was a significant difference in the completion time of the 4 x 50 m swim protocol between the control and experimental trials (1.54.28 vs. 1.52.85 min, p < 0.001).

Pre and post ingestion as well as post exercise values of acid-base equilibrium variables (HCO₃^-, BE, pH) are displayed in Figure 2 and 3. The results of ANOVA indicated a significant effect of sodium bicarbonate ingestion on blood concentration of bicarbonates (F_(2.28) = 18.06 p < 0.01, Figure 2). The post hoc analysis indicated no differences in the pre ingestion and post exercise state, while a significant difference between the control and experimental trial was observed in the post ingestion state (25.13 vs. 28.49 mM, p < 0.001). When considering base excess, it must be indicated that bicarbonate intake resulted in higher values in the post ingestion state and lower ones immediately after exercise, yet these changes were not significant. The ingestion of bicarbonate had a statistically significant effect on blood pH (F_(2.28)) = 10.02, p < 0.01, Figure 3). Sixty minutes after the ingestion of sodium bicarbonate, blood pH in the experimental trial was significantly higher in comparison to the placebo trial (7.41 vs. 7.33, p < 0.01).

The results of the ANOVA also revealed a significant effect of sodium bicarbonate ingestion on plasma lactate concentration (F_(2.28) = 17.81, p < 0.001) which only appeared in the 1^st minute after exercise cessation(13.06 vs. 11.27 mmol·l^-1, p < 0.001). No changes in LA concentration occurred in the pre- and post ingestion states (p > 0.05).

There is a growing body of evidence to suggest that induced metabolic alkalosis in adults improves performance in repeated short duration sprints, in single effort prolonged sprints and in prolonged intermittent exercise of high intensity (Hollidge-Horvat, 2000; McNaughton, 1992; Parry-Billings and MacLaren, 1986). Recently obtained results indicate that sodium bicarbonate supplementation can also improve 200 m freestyle performance time in elite male competitors (Lindh et al., 2008). In the present study, we extended these findings, showing that the ingestion of sodium bicarbonate is an effective means during high intensity swimming, which improves performance in well-trained youth athletes. This was evidenced in the present study by significant improvement of swim speed of the first 50 m sprint as well as the total time of the 4 x 50 m swimming test protocol following sodium bicarbonate ingestion (Figure 1). Furthermore, evidence in favor of beneficial effects of sodium bicarbonate intake include, significantly elevated blood bicarbonates and higher blood pH in the post-ingestion state, (Figure 2, 3) as well as elevated plasma lactate concentration after exercise. It is therefore sensible to postulate that the elevation of buffering capacity following bicarbonate intake can be also used in practice in youth athletes to increase training intensity and swimming performance in competition at distances from 50 to 200 m in which energy production relies to a significant extent on the glycolytic pathway within working muscle cells (Cairns, 2006; McNaughton, 1992).

Of interest is the fact that similar sodium bicarbonate ingestion in adult athletes as applied in our study, raises blood pH up to 7.48, increases resting blood bicarbonate levels to 32- 36 mM and maintains anaerobic glycolysis at a rate which results in plasma post exercise lactate concentrations of 22-28 mM (Gaul et al., 1995; Parry-Billings and MacLaren, 1986; Thomas et al., 2005). In our subjects the considered acid-base balance variables and lactate concentration were also affected significantly by the intake of sodium bicarbonate and the occurred changes revealed a similar pattern to that reported for adult athletes, yet the effects were less pronounced. The lower LA production seen in our study after high intensity exercise is not surprising, because it is a well documented fact that children and youth, whether trained or untrained have a significantly smaller anaerobic capacity than adults (Hebestreit et al., 1996). This is explained, at least partially, by lower activity of muscle glycolytic enzymes (Inbar and Bar-Or, 1986). This is in accordance with studies which show that lactate production during exercise and changes in glycolytic enzyme activity in both human and animals become increasingly more effective with age (Berg et al., 1986; Billat et al., 2003; Denadai et al., 2000). It was reported that in boys, plasma norepinephrine levels were positively correlated with testosterone levels (Rowland et al., 1996). These findings suggested that glycolytic performance of youth athletes was partially depended on hormonal status and might be attributed to maturity-related differences.

While lower glycolytic capacity and the restricted reliance on high threshold motor units during intensive exercise in immature subjects (Inbar and Bar-Or, 1986) may fully account for lower LA production seen in our study, the cause of diminished plasma sodium bicarbonate concentration remains to be investigated and explained. However, based on data available in literature, a few possible mechanisms may be taken into account for HCO₃^- down regulation. Ratel et al., 2002 suggested that the limited decline in pH may be due to a different time course of regulation of arterial pCO₂ by a greater ventilation compensatory response in children. In this regard, an important finding is that children breathe more during exercise to eliminate a given amount of CO₂ (Nagano et al., 1998) which in turn leads to a lower arterial pCO₂ set point (Armon et al., 1991; Cooper et al., 1987). Additionally, aforementioned studies also showed that in children arterial pCO₂ increased with age while the ratio of alveolar pCO₂ to VO₂ decreased at the ventilatory anaerobic threshold.

• Sodium bicarbonate is an effective ergogenic aid, also in youth athletes.
• Sodium bicarbonate intake improves swimming sprint performance.
• Sodium bicarbonate intake increases resting blood pH and bicarbonate level