He has played more samurai than even he can keep track of.

（彼は自分でも把握できないほどたくさんのサムライ役を演じてきた。）
　バッドマンの最新作「Batman Begins」についての記事より渡辺謙に関する紹介文から。

• "keep track of" の track は追跡するのニュアンスか。熟語で「〜の経過を追う／…を見失わないようにする／ずっと〜の情報を得る」。
  • Keep track of the time you work at the computer.
  • Please carefully keep track of your expenses during the trip.
  • It's difficult to keep track of all the new discoveries in genetics. （genetic：遺伝学の）
  • She had lost all track of time and had fallen asleep.
  • I just lost all track of time.