An old memory came to mind while watching some of the snowboarding events in the recent 2018 Winter Olympics. I noticed how some of the athletes would rhythmically sway their heads, arms and hips prior to a run. They seemed relaxed and calm. According to a commentator, they were listening to music under their helmets.
Many years ago, there was a fellow student at our university kendo club who, in a way, was ahead of the times. At one particular tournament, I remember seeing his eyes, face and demeanor behind the mengane. He seemed to be in the zone, focused and on a mission. He was on fire in his shiai‘s at the kyu or shodan level and he did well. If I recall correctly, between his shiai‘s, club members and I noticed the faint sound of music around him. We eventually discovered that he had been listening to his favorite heavy metal music while fighting!
In those days, the Walkman was the cutting-edge in technology. He had managed to fit earpieces or a headset with a line under his men and the portable tape cassette somewhere around his body.
Rest assured that he removed what could have been construed as a performance enhancing device. A senpai likely explained to him that it was not listed in the rule-book as an approved piece of equipment for shiai.
Certainly, music can inspire a person and/or calm the nerves. How creative of him.