Why L-glutamine for recovery In the 24-48 hours following exercise, it is critical that athletes address protein metabolism as it determines the impact on muscle hypertrophy. Amino acid availability, including L-glutamine, is an important regulator of muscle protein metabolism. Glutamine is one of the most abundant amino acids in the human body accounting for greater than 60% of the total intramuscular free amino acids in the body and virtually every cell uses it. During exercise, the body may be depleted of glutamine, therefore supplemental replenishment may be beneficial for athletes.