Forbes was an Australian men's gymnastics team member from 1975 to 1980 and during this period he represented Australia at the 1977 Summer Universiade in Sofia, Bulgaria, 1978 World Artistic Gymnastics Championships in Strasbourg, France, 1979 Summer Universiade in Mexico City and 1979 World Artistic Gymnastics Championships in Fort Worth, Texas. At the 1978 Commonwealth Games in Edmonton, Canada, he won a bronze medal in the men's team competition.