Disclosed is an amino acid composition when used non-therapeutically to improve endurance during exercise comprising the amino acids in the following amounts wherein the total quantity of the amino acids is 100 parts by mass； aspartic acid 3.0 to 10.0 parts by mass； threonine 2.5 to 9.0 parts by mass； serine 2.0 to 9.5 parts by mass； glutamic acid 12.0 to 40.0 parts by mass； proline 7.0 to 20.0 parts by mass； glycine 0.5 to 4.5 parts by mass； alanine 1.0 to 4.5 parts by mass； valine 3.0 to 12.0 parts by mass； cystine 0.1 to 0.8 part by mass； methionine 1.5 to 5.0 parts by mass； isoleucine 2.0 to 8.0 parts by mass； leucine 5.0 to 15.0 parts by mass； tyrosine 3.0 to 10.0 parts by mass； phenylalanine 3.0 to 10.0 parts by mass； lysine 4.0 to 15.0 parts by mass； tryptophan 0.8 to 4.0 parts by mass； histidine 1.5 to 5.0 parts by mass； and arginine 2.0 to 6.0 parts by mass. Further disclosed is a non-therapeutic method for improving endurance during exercise comprising administering the composition as defined above.
