Manuel, the first African-American woman to win individual Olympic swimming gold, had revealed after failing to reach the 100m freestyle final at the CHI Health Center that she had been diagnosed with "overtraining syndrome" and had had to take three weeks off during March and April.

After finishing in 24.29sec on the final night of the eight-day trials, the 24-year-old said: "That 50 may have been the longest 50 of my life."

Abbey Weitzeil, winner of the 100m freestyle, finished 0.01 behind her in second.

Caeleb Dressel matched his United States record of 21.04 with victory in the men’s 50m freestyle.

It was Dressel’s third victory at the trials, and he could also be involved in up to four relays in Tokyo.

Michael Andrew took second place in 21.48 to qualify for his third individual event at the Games, where he is also due to compete in one relay.

Nathan Adrian, seeking a fourth Olympic appearance after recovering from cancer treatment, just missed out on the top two qualifying places, clocking 21.73 for third place.

Bobby Finke won the final event of the trials, the men’s 1,500 freestyle, in 14min 46.06sec, half the pool ahead of Michael Brinegar, who claimed his Tokyo berth with a time of 15:00.87.