Adamson qualified for the marathon at the 1984 Olympic Games, where he finished 52nd in a time of 2:25:02. Later in the year, he was scheduled to compete at the 1984 New York City Marathon, but withdrew before the start as the weather was too warm. In the same year, he won the 1984 Philadelphia Marathon in a time of 2:16.39, a Jamaican national record in the event. In 1985, Adamson won the event for a second consecutive year in a time of 2:18:27, 5 minutes and 13 seconds ahead of anyone else. After the race, Adamson said that he had hoped to have run a faster time, but was slowed down by the wind. Adamson competed in the marathon at the 1988 Olympic Games, finishing 84th, and also ran the 10,000 metres at the 1990 Commonwealth Games, where he finished ninth.