The use of sodium bicarbonate to boost high-intensity exercise performance continues to tantalise despite its potential drawbacks. Andrew Hamilton looks at more recent research on our old friend and comes up with promising findings... MORE
Sports nutrition: does sodium bicarbonate supplementation improve performance?
It’s been used in baking for years and briefly found favour with athletes, but as Keith Baar and Andy Philp explain, new research suggests that taking sodium bicarbonate before you train really could lead to better endurance performance.
During intense training, our muscles produce a substance called lactate and hydrogen ions (acid) faster than we can use or get rid of them. The result is a build up of these by-products in the exercising muscle. People have long believed that this increase in acid and lactate is a direct cause of fatigue. However, scientists still argue over this point despite over a century of investigation.
Our bodies have a number of protective mechanisms that try to prevent the build up of acid. One of the most important of these is bicarbonate, which is alkaline – ie it helps neutralise acid. Bicarbonate is not only used as a raising agent in baking, but is also made throughout our bodies. One of the biggest bicarbonate producers is the stomach, where bicarbonate is made as a by-product in the process of making our digestive juices. After we eat, the rush to make stomach acid results in an increase in bicarbonate released into the bloodstream. This ‘alkaline tide’ is what makes us feel sleepy after a meal – not what will help us improve performance.
Bicarbonate in the body
During exercise, bicarbonate is initially made as a way to get rid of the carbon dioxide (CO2) produced by our muscles. The increased requirement for ATP to power our muscles results in an increase in CO2 production as a by-product of the breakdown of fats and carbohydrates. In the blood that feeds the muscle, CO2 and water (H2O) are converted to HCO3- (bicarbonate) and H+ (acid) by red blood cells using the enzyme carbonic anhydrase. At the lung, the reaction is reversed and the CO2 and water are released in the breath. This allows us to exhale the waste and maintain the correct acid/alkaline balance in our muscles.
For years, this was believed to be the reason that the lactate threshold and the ventilatory threshold coincided. The idea was that, at our lactate threshold, oxygen delivery to the muscles was insufficient and this resulted in a shift towards energy production without oxygen and the production of lactate and hydrogen ions. Since acid production was turned on, the increase in acid would mean the process above was accelerated, resulting in a sharp rise in ventilation.
While the theory of the relationship between the lactate and ventilatory thresholds makes sense, it doesn’t appear to be right. Newer studies show that oxygen delivery to the muscle is not limited during sub-maximal exercise, so that a lack of oxygen in our muscle cells isn’t what causes lactate production(1). What we really think causes both the lactate and ventilatory thresholds is a rise in the ‘fight or flight’ hormone called adrenaline, and a change in which muscle fibres we use. As the exercise intensity rises, we start to use more type II glycolytic muscle fibres. These fibres produce more lactate than type I or type II oxidative fibres, resulting in increased lactate accumulation in the blood.
At the same time, there is a sharp rise in adrenaline. This is because as the intensity of exercise increases it becomes a greater stress on our body and this activates the flight or flight response: releasing adrenaline. The rise in adrenaline causes our muscles to break down stored carbohydrate (glycogen) faster and decreases blood flow to the liver and kidneys (where lactate is normally removed from the blood), contributing to the accumulation of lactate. Adrenaline also directly increases our respiratory rate, contributing to the ventilatory threshold.
Bicarbonate and performance
No matter their cause, lactate and ventilatory threshold play a significant role in performance. The higher that we can get our speed/power at lactate threshold, the better our performance will be. Therefore, if we can focus our training on increasing speed/power at lactate threshold, we can maximise our performance adaptation.
One way might be to boost the amount of bicarbonate that we have in our blood on the day of the big event. The extra bicarbonate should buffer the acid our muscles produce and therefore increase the intensity we can maintain before lactate begins to build up in our blood.
People have tested the effects of bicarbonate on performance for over 75 years, on the premise that acid accumulation limits our endurance performance.
In 1931, scientists showed that drinking a solution that contained baking soda (sodium bicarbonate or bicarb) prior to exercise could improve running performance (2). These experiments were confirmed 2 years later, but a huge amount of conflicting research in the following 75 years has made people question whether bicarb can really be used as an ergogenic aid.
Beyond the scientific uncertainty, one of the biggest concerns with using bicarb on the day of performance is that drinking large amounts of baking soda can cause severe intestinal distress (read bloating, nausea and diarrhoea). Since these types of complications are the last thing anyone wants to have to deal with on the day of competition, a lot of athletes have quite understandably shunned the use of bicarb (but see box 1 for tips on decreasing intestinal problems when taking bicarb).
Bicarb training research
While the effects of bicarb on the day of the competition are uncertain and the potential negative effects on the gut might make an athlete unlikely to use bicarb for an important event, there might be good reasons to use bicarb during training. In the last three years, two studies have come out showing that taking bicarbonate during training improves performance.
In the first study, 16 moderately trained women exercised three times a week for eight weeks(3). One group drank a bicarb solution at 90 and 30 minutes prior to performing each high-intensity interval training session (containing 0.2g of bicarb per kilo of bodyweight) while group two drank a similar tasting salt solution.
In weeks one and two, each subject performed six to nine 2-minute intervals on a bike at 140% of their initial power at lactate threshold. The number of intervals and the relative intensity increased every second week until they were performing twelve 2-minute intervals at 160% of the power at lactate threshold in week seven. For week eight, the number of intervals was decreased to six to nine again, but the power was increased to 170%. Before and after training the subjects performed both a graded exercise test for peak VO2 and a time to fatigue test to measure endurance.
In the group that took the bicarb, the alkalinity, the concentration of bicarb, and the amount of lactate in the blood was higher during each training session. This tells us that the drink was absorbed and had the effect of making the blood less acidic. After the 8-week training programme, both groups improved their peak oxygen uptake (VO2) by approximately 18%. However, the group that took bicarb before each training session improved their power at lactate threshold 9.6% more than the group that took the saline solution.
As discussed above, power at lactate threshold is one of the most important parameters for determining endurance performance. Therefore, it was not surprising to see that the bicarb group showed a 41% greater improvement in time to fatigue (see figure 1). While this isn’t a direct measure of performance, the increased endurance and improved power at lactate threshold are strongly associated with better performance.
After discovering that drinking bicarb during training improved performance in humans, some of the same scientists went on to try to determine how bicarb might be exerting its positive effects (4). To do this, they switched from people to rats, allowing a more controlled experiment and detailed analysis of muscle adaptation to training. They split the rats into three groups:
- A control that didn’t exercise or take bicarb;
- An exercise group that drank water;
- An exercise group that drank a bicarb solution 30 minutes before exercise.
Like the human subjects in the first study, the rats increased their training from six to twelve 2-minute intervals, but with a running speed increase of 37 to 52 metres/min over the five weeks of the study.
At the end of training, the bicarb-drinking group had increased the number of mitochondria in one of their running muscles 7.5% more then the water group even though the animals did exactly the same amount of work. The authors of the study also found that the bicarb group increased the production of the transporter protein called MCT4, which helps remove lactate from the muscles (see figure 2). The fact that there was a greater rise in mitochondria tells us that adding baking soda to your training schedule would result in better performance even if you were to do no more work.
When we saw this data, we were excited by the fact that simply adding bicarb increased the number of mitochondria in muscle. The fact that they only measured this in a ‘slow’ muscle was interesting because we think that the greatest effect would be in fast twitch muscle where the ability to increase mitochondria is the strongest. Since the number of mitochondria in our fast muscles is one of the best determinants of speed/power at lactate threshold, we wondered whether the improved performance was due to a direct effect of bicarb on our mitochondria.
To study this question, Andy Philp performed a series of experiments on isolated muscle cells. The logic is that if bicarb is exerting its benefits on muscle cells and not the whole body, by just feeding the cells bicarb, we should see the same effects that the researchers above saw in people and rats.
So, Andy set up a (as yet unpublished) cells study in which one cell culture got a salt solution and the other got a solution containing about the same amount of bicarb as would have been circulating in the human study (3). After three days of treating the cells in this way, we saw an increase in the amount of mitochondrial protein in the cells of approximately 50% (see figure 3).
The reason for this increase in mitochondrial protein appears to be that bicarb is able to directly turn on a regulator of the number of mitochondria in our cells. The amount of this protein, PGC1alpha, is one of the most important factors in making new mitochondria. Simply adding bicarb to the cells resulted in a 5-fold increase in PGC1alpha. This increase in PGC1alpha is almost identical to what is seen after endurance exercise. These data tell us that simply taking bicarb may provide some of the same effects as exercise!
The other interesting findings from this study are that the cells that got the bicarb treatment consumed more energy at rest, they were better able to transport glucose, and they contained more of the glucose and lactate transporters. This tells us that after three days treatment with bicarb, the cells looked more like those in the muscles of an endurance athlete, because endurance athletes have a higher resting metabolism and are better able to take up lactate and sugar from the blood.
The last question that remained was whether the adaptation is a direct effect of the bicarb or whether it is an effect of increasing the alkalinity around the cells. To study this question, Andy employed another popular agent used to control acid/alkaline balance, called sodium citrate. When Andy did the same experiments using citrate, he saw a small increase in PGC1alpha, but not as much as during the bicarb experiments. So, this means that it’s the bicarb that acts directly on our muscle cells to increase mitochondria rather than any change in acid/alkaline balance.
Drinking baking soda solution before exercise means that there is high bicarb concentration in the blood during exercise. Doing high intensity intervals directs that blood to the ‘fast twitch’ muscle fibres (that do a lot of the work at high intensity). The bicarb is taken up in these fast fibres and acts to increase the mitochondrial controller (PGC1alpha). The increase in PGC1alpha signals these fast fibres to make more mitochondria. As discussed above, power at lactate threshold reflects the amount of mitochondria we have in our fast twitch muscle fibres. Therefore, by targeting these fibres with training and nutrition, we can improve their adaptation and, by extension, our performance.
So using sodium bicarbonate during training could be an inexpensive but powerful tool to add to your training regime. It would have a positive effect at any point in training, but the biggest effect on performance will be when you are trying to improve speed/power at lactate threshold using high intensity workouts.
Keith Baar runs the functional molecular biology laboratory at the University of California.
Andrew Philp is a postdoctoral fellow at the University of California and has performed all of the experiments on the effects of bicarb on muscle mitochondria. Both authors are scientific consultants with the English Institute of Sport and British Cycling.
1. J. Appl. Physiol. 1998 85: 627-634
2. J Clin Invest. 1931 9: 601-13
3. J Appl Physiol. 2006 101: 918-25
4. Am J Physiol Endocrinol Metab. 2007 293: E916-22