If music is useful for your triathlon training or running training, why on earth do the organizers of races not allow to use MP3 players on the race lane? 2007 NY Marathon forbid music during the run with a lot of news headlines (one idea behind the ban is to limit tactical communication between coaches and their athletes).
But music can have a significant effect on your training. Music can drag your attention back to your training when you start getting fatigue. Music in your triathlon training can positively influence your emotions (most athletes hear loud, beat-up music) to “psych up” them. The tempo of your music can regulate your movements and prolong your performance. There are some more positive effects of music on your training, if you’re interested in the scientific background, read this article of the SportJournal.
Select the type of music for your training based on the type of activity and the intensity.
Here are some playlists of athletes:
Be careful will using your MP3 during training (especially bike training) that you don’t overhear the traffic around you and please always read the regulations of your races before you use your MP3 player during a race.