Lermusiaux won his preliminary heat of the 800 metres with a time of 2:16.6. This qualified him to compete in the final, but Lermusiaux chose not to do so.
In the 1,500 metres, which was run in a single heat, Lermusiaux lead for most of the race. In the final straight, he was passed by Edwin Flack (Australia) and Arthur Blake (USA), and finished third. His time was 4:37.0 for the race.
In the military rifle shooting event, Lermusiaux's place and score are unknown, though he was not among the top 13 in the 42-man competitions.
Lermusaiux's final competition of the Games was the marathon. He led for 32 kilometres, dropping out with only 8 remaining.