Introduction
Many team and individual sports require short bursts of high intensity movements interspersed with periods of reduced intensity or complete rest. These short intense bursts of movement rely mainly on the two anaerobic energy systems: the phosphocreatine system and anaerobic glycolysis. The phosphocreatine system is significantly limited in duration, providing only a few seconds of energy (generally 10 seconds or less). Glycolysis allows for more energy production and henceforth provides greater sustainability of movement. With this increased sustainability, greater amounts of byproducts are produced. The byproducts of anaerobic glycolysis include intracellular accumulation of hydrogen ions and lactate. Specifically, hydrogen ions have been one of many different factors believed to contribute to muscle fatigue. Intracellular accumulation of hydrogen ions can depend on the extracellular hydrogen concentration. During high intensity exercise, extracellular hydrogen ion concentrations are high. This high extracellular accumulation of hydrogen inhibits the hydrogen efflux out of the muscle cell. The increased extracellular hydrogen results in a lowering of blood pH (greater acidity), which is negatively associated with an athletes repeat sprint performance. One theoretical method to combat the negative effects of hydrogen accumulation is to ingest alkaline nutritional supplements. Theoretically, these alkaline substances would act as a natural buffer by accepting the hydrogen ion and neutralizing it. This would allow the muscle cell efflux to continue to remove intracellular hydrogen and ultimately delay the onset of fatigue. A nutritional supplement being explored in this capacity is sodium bicarbonate. The ingestion of sodium bicarbonate raises the amount of bicarbonate in the blood (HCO3-). This alkaline molecule neutralizes extracellular hydrogen by converting it into carbonic acid and eventually into carbon dioxide and water. This in turn promotes greater efflux activity. Previous research has supported this theory, as generally higher amounts of lactate are found in the blood post sodium bicarbonate ingestion and exercise, suggesting greater efflux activity (hydrogen and lactate are exported together). However, there has not been any research which has examined the mechanisms which alkalosis improves repeat sprint performance. Therefore, the purpose of this study is twofold. First, to investigate if sodium bicarbonate improves sport simulated repeat sprint performance. Second, to investigate the mechanisms which sodium bicarbonate may induce this improvement.
Purpose: The purpose of this research study is to a.) examine the effectiveness of sodium bicarbonate on repeat sprint ability and b.) to examine the mechanisms by which sodium bicarbonate may induce performance enhancement.
Subject Description: Ten recreational, team-sport playing females volunteered for this study. The mean age of the subjects was 19 ±1 year. The mean body mass was 64.3 kg ± 10 kg. The mean VO2max was 49.4±12.8 mL·kg-1 ·min-1. The mean lactate threshold was 34.5±10.2 mL·kg-1 ·min-1.
Procedures and Methods: The study was a random counter-balanced design consisting of a total of three testing sessions. A minimum of 48 hours between the baseline test and follow-up testing was required and a minimum of a week between the two testing sessions. The study was initiated with a baseline graded exercise test to determine lactate threshold and VO2max. The graded exercise test was performed on an air-braked track-cycle ergometer and consisted of graded exercise steps for four minutes with intermittent rests of one minute between bouts. The test started at 50W and was increased 30W after each four minute bout until volitional exhaustion. The subjects were required to maintain the current power output. Lactate threshold was calculated using the modified Dmax method. VO2 was calculated using the continuous analysis of O2 and CO2 during the test using Ametek analyzers. Ventilation was recorded every 15 seconds using a ventilator. The sum of the four highest consecutive 15s values was used at the VO2max.
Supplementation consisted of either 0.3 g·kg-1 NaHCO3 or 0.207 g·kg-1 of NaCl (placebo) with 500 mL of water 90 min before performing the RSA test.
Testing started with a 5 minute cycling warm-up and three practice sprints. The subjects then performed a 10s maximal sprint test on a cycle ergometer. The total work was recorded in the first 6s of the 10s sprint was used as the criterion score during the following five, 6s cycle tests. After the 10s sprint the subjects were given 5 minutes of rest. Testing consisted of five, 6s maximal sprints with 24s passive rest between sprints. Subjects were required to achieve 95% of their criterion on the first sprint. Sprints were performed in the standing position and verbal encouragement was given to subjects.
50L of blood was collected during the initial baseline test and 100L during the testing sessions. Blood samples were taken at rest and immediately post sprint testing. Blood pH was determined using a Ciba Corning blood gas analyzer.
Muscle biopsy was performed during the two testing sessions. The first sample (50-80mg) was taken before wam-up and the second (50-80mg) immediately post session. The samples were freeze-dried and dissected of connective tissue and blood.
Muscle buffering capacity was measured by taking freeze dried muscle samples and placing them in 30 mg dry muscle ·mL-1 of homogenizing solution. The solution was placed in a bath at 37°C for 5 minutes prior to measuring pH. pH was measured using a microelectrode connected to a pH meter. The solution was titrated and the number of moles of hydrogen ions was measured. Freeze-dried samples were also used to determine lactate levels. Buffer capacity was estimated from the changes in lactate and pH.
Results: Sodium bicarbonate significantly reduced blood hydrogen concentration (37.2 ± 0.5 vs 31.5± 0.8 nmol·L-1 ; P< 0.05) and increased HCO3– concentration (23.6 ± 1.1 vs 30.0 ± 3.0 mmol·L-1 ; P<0.05) with no changes noted in the control group. Posttest hydrogen and sodium bicarbonate were also significantly lower and higher in the supplement group verses control (p<0.05). After sprint testing, lactate concentrations were significantly higher in both groups (P<0.05). Lactate concentration in blood sampling was 28% higher in the supplement group verses control (p<0.05). Posttest muscle lactate concentration also was 72% higher in supplement than placebo (P< 0.05). Total work was significantly higher in the supplement group verses the control (p<0.05). This was mainly due to increases in sprints 3, 4, and 5. Peak power was also significantly improved during these sprints (P<0.05).
Discussion: Ingestion of sodium bicarbonate successfully demonstrated the ability to raise blood levels of bicarbonate and reduce hydrogen ion concentration. Interestingly, muscle levels of hydrogen ions and lactate remained unchanged at rest. Posttest revealed a 72% increase in muscle lactate and a 28% increase in blood levels. This was the first study to reveal the effects of metabolic alkalosis on muscle lactate levels. The increased levels of lactate in the blood are most likely due to changes in lactate clearance to the blood (increased efflux). The reasoning for higher levels of lactate in the muscle are less clear. It is hypothesized that increasing metabolic alkalosis increases the muscle’s use of glycogen as fuel thereby increasing lactate byproduct. As expected, ingestion of sodium bicarbonate resulted in higher blood pH levels posttest. This can be contributed to the reduction in posttest blood concentrations of hydrogen ions. Additionally, there was a greater change in muscle lactate concentration for the same change in muscle pH, suggesting a higher pH in muscle. These results suggest that a critical level of muscle pH may limit repeat sprint performance. Lastly, the increased amount of work and power output demonstrates that metabolic alkalosis helps delay the onset of fatigue. In conclusion, supplementation of sodium bicarbonate appears to positively influence both blood and muscle pH levels and improves repeat sprint performance in recreational female athletes.
My Thoughts: Overall, I think it is pretty amazing a supplement as simple as baking soda has flown under the radar for so long. Especially with most of the overall data being positive. It would be interesting to see if sodium bicarbonate would positively influence events dominated by anaerobic glycolysis such as the 400 or 800m races. Another area I think would be interesting to study would be resistance training in the 8-20 rep range. It seems plausible that sodium bicarbonate would increase repetitions to failure. Additionally, with the increased usage of glyocogne, lactate buildup, and overall repetitions, it would seem reasonable to believe increases in muscle hypertrophy could be obtained. The limitations of this study include only having one sex and a small number of participants. Furthermore, the subjects were not highly trained. It is possible highly trained individuals may already be nearly optimal in their ability to efflux ions and therefore wouldn’t derive any benefit from further alkaline supplementation.
BISHOP, D., EDGE, J., DAVIS, C., & GOODMAN, C. (2004). Induced Metabolic Alkalosis Affects Muscle Metabolism and Repeated-Sprint Ability. Medicine & Science in Sports & Exercise, 807-813. doi:10.1249/01.mss.0000126392.20025.17
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