I rewatched the Thrilla in Manila with Muhammad Ali. He still winced at the blows years later

This week marks the 50th anniversary of one of boxing's greatest fights. As Muhammad Ali's biographer, I knew the toll the bout took on him

In 1989, with Muhammad Ali sitting beside me, I watched a tape of Ali's historic triumph over Joe Frazier in Manila, which took place 50 years ago this week.

For months, Ali and I had been reviewing his fights for a book I was writing as his authorized biographer. We'd watched Henry Cooper knock Cassius Clay to the brink of oblivion with a picture-perfect left hook. From the vantage point of my living room, that had amused Muhammad.