There are a lot of research in processes of pain modulation and pain perception that are modulated by serotonin and also on relation between brain serotonin and L-tryptophan biodisponability.
The daily tryptophan requirements are approximately 3.5 mg per kilogram weight by adults (Wurtmann et al., 1981).

Plasmatic tryptophan has a free form or is bounded to albumin. Free tryptophan, which some authors consider to be the most available form of transport to   the brain, means only 15-20% of the whole plasmatic tryptophan (Wurtmann et al., 1981).

The positive effect of tryptophan on tiredness can be explained through the capacity of the serotonin, a brain neurotransmitter produced from tryptophan, to reduce nociceptic transmission, which comes from muscle, tendons and ligaments under effort conditions, during physical training. A decrease of tiredness perception raises, indirectly, physical performance and wellness feeling. A supplement of vitamin-T® favours the transformation process of tryptophan to serotonin since it contains tryptophan and those vitamins related with this process.