TweetBuffering Agents and Exercise Performance



1. How do buffering agents work?

During high intensity exercise, the main source of energy is rapid glycolysis, a process that results in the production of high amount of lactate anions and hydrogen ions. In turn, the eventual buildup of these ions is thought to contribute to muscular fatigue by reducing muscle and blood pH levels, a state called metabolic acidosis. Buildup of hydrogen ions can inhibit glycolysis by inhibiting the activities of phosphofructokinase and phosphorylase, inhibit calcium binding to troponin C and its release from the sarcoplasmic reticulum, and reduce muscle contractile force [1-2]; all of these can result in increased fatigue and reduced performance.

Given that acidosis is responsible for many of the processes that can contribute to muscular fatigue, preventing this state may improve performance. This is the rationale for the use of buffering agents, which can counteract the exercise-induced decrease in muscular and plasma pH. The two most popular buffering agents used for this purpose are sodium citrate and sodium bicarbonate (baking soda), and research has consistently found that oral administration of these substances in sufficient quantity prevents the exercise-induced decrease in pH levels. These agents function both by facilitating lactate efflux and by increasing glycolytic energy production [2-5].

Mechanisms for improved performance other than increased peripheral buffering capacity have also been postulated. Buffering agents may also influence the afferent stimulation from contracting muscles, causing a change in the hormonal and central response to exercise [2]. High sodium intake also leads to increased plasma volume, which may improve perfousion of skeletal muscle and alter sensory feedback to the brain [2], but it is unlikely that this is the only effect, since many studies finding improved performance from buffering agents use sodium chloride as a positive control.

2. Are buffering agents effective for all types of exercise?

Studies have been done on the use of buffering agents for many types of exercise. In theory, buffering agents would be primarily useful for short-term, high-intensity, intermittent exercise where glycolytic energy production is a major limiting factor. In support of this, the largest effect is generally seen with exercise bouts lasting one minute up to 4-8 minutes [4-5]. Buffering agents are less effective for exercise bouts of shorter duration; this may be because such exercise does not sufficiently challenge intrinsic buffering capacity and/or because rapid glycolysis is not as important of an energy source during this type of exercise. Sport specific protocols have found that buffering agents improve performance in sprinting, interval swimming, rowing, and cycling [5]. There are trends toward a greater effect in repeated, high intensity exercise vs. single, exhaustive bouts, in upper body exercise as compared to lower body exercise, and in less trained individuals, presumably because they do not have as high of a natural buffering capacity [5]. Even with high-intensity, intermittent exercise, some studies do not yield positive results [6], but this may be explained by use of a dose lower than the ideal [3], inadequate sample size, inadequate study duration (the effect is more pronounced during later exercise bouts), or differing study design.

More recent research has addressed a possible performance enhancing effect for endurance exercise. There is evidence that during endurance exercise, despite reliance on aerobic energy production, anaerobic glycolysis still plays a significant role, as evidenced by increased lactate concentration [2]. Some studies on the effects of buffer ingestion on endurance exercise have found no benefit, but others have yielded promising results. It has been pointed out that in studies that showed no effect, subjects were not allowed to alter their running pace, which is not representative of real world conditions [2]. In one study, trained cyclists performed 30-km time trials in a crossover design, and the average time was significantly faster after citrate ingestion (57:36.6 min:s compared to 59:22.3 min:s) [1]. Other studies have also found improved performance in both intermittent and steady state prolonged exercise after buffer ingestion [1-2, 7].

3. What is the optimal dosage to use for increased performance?

Of course, not all of the news is positive. The amount of sodium citrate or bicarbonate required to significantly increase exercise performance is substantial. The effective dose falls in the range of .2-.6 g/kg of either substance – for most individuals, this will be 15 grams at the very least. Doses this high can lead to significant gastrointestinal discomfort.

Studies that have compared doses indicate that the optimal dose for performance is in the .4-.6 g/kg range. One study found that .6 g/kg of sodium citrate lead to the optimal changes in blood pH, while another found improved one minute spring performance in the .3-.5 g/kg range, with the greatest effect at .5 g/kg [1]. Another study reports that .5 g/kg sodium citrate is the ideal amount for changing blood pH [2]. For sodium bicarbonate, the lowest reported effective dose was .2 g/kg in one trial [1]. However, other literature indicates that .3 g/kg is not as effective as higher doses [3], and most studies utilize .3-.5 g/kg. It would appear that from a performance standpoint, .5 g/kg of either substance is optimal, while .3 g/kg, and possibly .2 g/kg, can still be of benefit. Doses lower than this are unlikely to change pH enough to significantly improve performance.

Research has also been done on the optimal timing of ingestion, which falls in the range of 1-3 hours before exercise [7]. In one study, ingestion of .5 g/kg sodium citrate lead to an optimal alkalotic state 100-120 minutes after ingestion [2] – but one must keep in mind that having this period coincide with the later period of exercise would be ideal, so for a 45 minute training session, for example, one would want to consume the buffering agent 80-90 minutes before exercise.

The performance standpoint is not the only one that should be taken into consideration. Reports indicate that gastrointestinal discomfort is quite common, although it generally occurs in the first hour after ingestion, and therefore shouldn't coincide with the exercise period [2]. The best way to reduce this side effect is by lowering the dose. Reports of gastrointestinal discomfort and stomach cramps are much more common after .6 g/kg sodium citrate than .4 g/kg (five of eight subjects complaining versus two of eight) [1]. This effect may also be worse with sodium bicarbonate [2]. In three trials with .5 g/kg sodium citrate, one reports GI discomfort in 3 of 8 subjects while the other two report no problems [2]. It would appear that .4 g/kg sodium citrate is a relatively comfortable dose, with .5 g/kg still being tolerable to many. Since individual reactions can vary, experimentation is necessary to determine the highest tolerable dose.

A final issue is whether or not chronic ingestion is superior to acute ingestion. To answer this question, a study was conducted comparing .5 g/kg sodium bicarbonate acutely or over a period of six days on 90 second maximal cycling performance. Both groups had improved performance, but performance was still increased two days after chronic supplementation was discontinued [8]. This indicates that chronic ingestion of buffering agents may yield a greater and longer lasting effect. It is also possible that the required dosage needed for a benefit is lower with chronic ingestion.

4. What type of buffering agent is best?

Many forms of citrates and bicarbonates are available, including sodium, potassium, calcium, and magnesium. Although the research in athletes has been carried out with sodium citrate and bicarbonate, the other forms will presumably have the same effect.

A gram of calcium daily can be taken safely. Some people are comfortable taking more, while others are not. Some literature recommends that those on high protein diets take a gram of calcium per 50 g protein to begin with. Magnesium can then be added in a 2:1 calcium:magnesium ratio, although greater amounts are acceptable. Too much magnesium has a laxative effect.

Sodium and potassium are two electrolytes commonly recommended during endurance exercise. There is now substantial evidence that many endurance athletes, especially those who are less experienced, do not consume enough sodium during exercise, which can result in hyponatremia (low blood sodium), which has dangerous or even fatal effects. Hyponatremia is most common in endurance athletes, military trainees, and hikers. Although the common perception is that electrolytes should be supplemented during exercise because they are lost in sweat, the majority of cases of hyponatremia are due to fluid overload. This is because a large amount of secondary literature urges athletes to consume too much water during exercise. Most organizations and researches recommend that water intake be in the range of .5-1 liters hourly during exercise. Additionally, each liter of water should contain 400-800 mg, more than in most sports drinks. Thus, supplementation with sodium citrate or bicarbonate will provide more protection against this condition. [9-12]

In contrast, large amounts of potassium supplements are strongly discouraged during intense exercise. Exercise causes the release of potassium from muscle cells, which elevates blood levels of potassium (known as hyperkalemia). This is rapidly corrected after exercise is completed, but hyperkalemia has been linked to some cases of sudden death and other incidences of cardiovascular problems in endurance athletes with cardiovascular conditions. It is doubtful that this is a significant risk in healthy individuals, but there is no reason to worsen the situation by consuming a large amount of potassium supplements, which will significantly elevate blood levels of potassium leading to an additive effect. Potassium supplements after exercise and during other periods are acceptable, and in some cases recommended. [12]

In summary, the use of buffering agents has the potential to improve performance for many types of exercise. The optimal dosage is .5 g/kg of sodium citrate or sodium bicarbonate; although other buffering agents (such as calcium or magnesium citrate) presumably work, they have not been tested. This dose should be worked up to until the maximum tolerable dose is achieved, and sodium citrate may be more tolerable than sodium bicarbonate. Chronic ingestion may cause a further increase in exercise performance.