In 1976, still only 21 years old, Brydenbach competed at the 1976 Summer Olympics in Montreal. After running in 45.28 seconds in the semi-final, he improved to 45.04 seconds in the final race. He finished fourth, but the time was a lifetime best result. It was a Belgian record, and stood until 2003 when Cédric Van Branteghem broke it. He came close to improving the result at the 1980 Summer Olympics, where he finished fifth in the final with 45.10 seconds. He also competed in the 4 x 400 metre relay, but the team failed to finish. The next year he contributed to a Belgian record in this event—3:03.68 minutes, which stood until 2008. Brydenbach also won the gold medal at the 1977 Summer Universiade. His new championship record of 45.18 seconds stood for two years.