At least that's what Eva Blomstrand suggest in her paper A Role for Branched-Chain Amino Acids in Reducing Central Fatigue.
The theory is that exercise increases the uptake of tryptophan by the brain leading to increased 5-HT levels which has been suggested to cause fatigue.
Exercise causes an increase in neurotransmitter release. Among those neurotransmitters is 5-hydroxytryptamine (5-HT) which is involved in the control of arousal, sleepiness, mood and possibly fatigue. Exercise also causes an increased uptake of BCAAs to the muscle, which decreases plasma concentration. Exercise also elevates the plasma level of fatty acids and typtophan. The author postulates that by elevating the plasma concentration of BCAAs it will decrease the transport of tryptophan into the brain. This decrease in tryptophan is relevant because the rate-limiting step in the synthesis of 5-HT is the transport of tryptophan across the blood–brain barrier.
So by increasing plasma concentration of BCAAs it will reduce the uptake of tryptophan by the brain and consequently reduce 5-HT synthesis which will result in the delay of fatigue.
The theory is that exercise increases the uptake of tryptophan by the brain leading to increased 5-HT levels which has been suggested to cause fatigue.
Exercise causes an increase in neurotransmitter release. Among those neurotransmitters is 5-hydroxytryptamine (5-HT) which is involved in the control of arousal, sleepiness, mood and possibly fatigue. Exercise also causes an increased uptake of BCAAs to the muscle, which decreases plasma concentration. Exercise also elevates the plasma level of fatty acids and typtophan. The author postulates that by elevating the plasma concentration of BCAAs it will decrease the transport of tryptophan into the brain. This decrease in tryptophan is relevant because the rate-limiting step in the synthesis of 5-HT is the transport of tryptophan across the blood–brain barrier.
So by increasing plasma concentration of BCAAs it will reduce the uptake of tryptophan by the brain and consequently reduce 5-HT synthesis which will result in the delay of fatigue.