PROBLEM TO BE SOLVED: To provide an anti-fatigue agent which can prevent both of muscle fatigue and nerve strain concurrently.SOLUTION: The invention provides an anti-fatigue agent which prevents both of muscle fatigue and nerve strain concurrently, the agent containing an amino acid composition consisting of specific kinds and specific amounts of amino acids. As for the kinds and the ratio of the amounts of the amino acids contained in the amino acid composition, the amino acid composition preferably contains 30 to 200 pts.wt. of proline, 60 to 140 pts.wt. of glycine, 25 to 260 pts.wt. of alanine, 40 to 130 pts.wt. of lysine, 20 to 75 pts.wt. of tryptophan and 15 to 40 pts.wt. of histidine, preferably further contains 35 to 65 pts.wt. of threonine, 15 to 65 pts.wt. of tyrosine, 25 to 45 pts.wt. of arginine, and preferably still further contains 30 to 55 pts.wt. of valine, 35 to 60 pts.wt. of leucine and 25 to 45 pts.wt. of isoleucine.【課題】筋肉疲労と神経疲労との双方を同時に防止することが出来る疲労防止剤の提供。【解決手段】特定種・特定量のアミノ酸からなるアミノ酸組成物を含む、筋肉疲労と神経疲労との双方を同時に防止する疲労防止剤。好ましいアミノ酸種と量比としては、プロリン３０～２００重量部；グリシン６０～１４０重量部；アラニン２５～２６０重量部；リジン４０～１３０重量部；トリプトファン２０～７５重量部；ヒスチジン１５～４０重量部を含むアミノ酸組成物。さらスレオニン３５～６５重量部；チロシン１５～６５重量部；アルギニン２５～４５重量部を含むことが好ましく、またバリン３０～５５重量部；ロイシン３５～６０重量部；イソロイシン２５～４５重量部を含むことが好ましいアミノ酸組成物。【選択図】なし
