Modra began pole vaulting in 1987 and won the pole vaulting competition at the 1989 Australian All-School Championships. He competed in athletics at the 1988 Seoul Paralympics where he competed in the Men's 1500 m B3 and Men's Javelin B3. He took up swimming to aid his recovery from a knee injury, and began competing in the sport in 1990. At the 1992 Paralympics in Barcelona, where he competed in both athletics and swimming, he won two bronze medals in the Men's 100 m Backstroke B3 and Men's 200 m Backstroke B3 events.