Complex sentence: Hart continued to train and improve his abilities and by 1937 he was the Dominion welterweight champion, also in 1937 he won a gold medal in the welterweight class from the Amateur Athletic Union of Canada.
Split into simpler sentences: Hart continued to train and improve his abilities and by 1937 he was the Dominion welterweight champion. In 1937 also he won a gold medal in the welterweight class from the Amateur Athletic Union of Canada.