4 min read

Triumph Over Exhaustion with BCAA

Tomasz Jankowski ✓

Diets Premium Expert • 22.03.2026

✓

Scientifically reviewed by a clinical dietitian: This article has been peer-reviewed for adherence to IŻŻ, WHO, and PTGiP clinical nutritional standards.

Diets Premium Expert Tomasz Jankowski

min read 4 min

Scientifically reviewed by a clinical dietitian 22.03.2026

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Key Takeaways

Lack of stimulation, loss of focus, and even excessive perspiration affects everyone's training. Some experience it more frequently, but no one is immune to occasional motivation dips. Is it the fault of idleness and the mental weakness that we've created ourselves? No. Contrary to popular opinion, it's not also the fault of inclement weather. Each of us has the right to have a bad day where our 100% is not as it usually is. Thanks to the advancements in human sciences, we are gradually beginning to understand what the causes of such bad days might be - which means that we can also counteract them and fight against perspiration attacks. Fascinatingly, a strong weapon in the fight for effective workouts turns out to be a substance that typically does not possess stimulating properties, namely BCAA.

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Types of exhaustion experienced during physical exercise

"I'm exhausted" – those are words that not only make a weak excuse for not wanting to continue training, but also make a very inaccurate description of our current physiological state. We can be more precise by saying that we feel high peripheral or high central fatigue. Both types of fatigue will lead to a decrease in intensity of training, and ultimately to its cessation, but on a physiological level, they are completely different. Muscles require increased energy expenditure to perform repeated contractions during training. Muscles utilize all sources of energy to enable the work ordered by the brain. Small reserves of adenosine triphosphate are used up first, but after a few seconds, phosphocreatine must be added and replaced by glucose. During training with lower intensity, but longer duration, muscles are more likely to use fat to power the training. Although nature has given us so many versatile sources of energy, they will eventually be significantly reduced and even exhausted during long and intense training. Then it can come to a situation where we are motivated to continue training, but the muscles simply do not have the energy to continue working.

Reciprocal interaction between BCAA and serotonin

The process of serotonin synthesis in the brain is a multi-step process, but the first step is catalyzed by the enzyme hydroxylase tryptophanase, and as the name suggests, the substrate used in the process of synthesizing serotonin is tryptophan. It is one of the essential amino acids, with several unique characteristics. The first is that tryptophan is the only amino acid transported in the bloodstream by binding to the transport protein albumin. Only about 10% of tryptophan is transported into the bloodstream in this form, and will not be bound to albumin. Free tryptophan can cross the blood-brain barrier, entering the brain where it is further converted to serotonin. This transport to the brain is regulated by several factors, including the ability of blood-brain barrier transporters, the concentration of free tryptophan in the blood, and also the presence of other large, neutral amino acids such as leucine, valine, and isoleucine, the branched-chain amino acids BCAA. These are transported via the same route as tryptophan, hence they compete for the attention of these transporters. This is important from the perspective of central fatigue, as supplementation with BCAA will lead to an increased ratio of BCAA: free tryptophan in the blood, leading to limited transport of tryptophan, conversion to serotonin, and reduction of central fatigue during training.

Practical Directives

The physiological processes described above do indeed seem to be applicable in practice. Human studies indicate that the BCAA mixture taken during physical activity helps to lessen fatigue. In one study, when testing the time to exhaustion in endurance training, BCAA supplementation helped to prolong training from 137 to 153 minutes. However, these results were obtained in people who trained at elevated temperatures. The results were not so clear in lower temperatures. This observation is supported by Professor Yannis Pitsiladis, who noticed an increase in serotonin levels in the brain during training at 30°C, but not at 10°C, in his study. Of course, in order to benefit from the aforementioned advantages, BCAA should be taken before training or possibly at the start of training. The recommended dose is 5 to 10 g BCAA per serving.