According to some experts, music makes running very easy, as per studies, music decreases your perception of how hard you have been running by around ten per cent. There is a scientific reason too behind it. Any external force like music creates certain blockage to some of the internal stimuli which is trying to reach the brain like tiredness from muscles to other organs. As these messages get blocked, you also feel like you can run more and more with very little or without any tiredness. Secondly music also makes your mood better like happiness and excitement and negates any effect of tension, confusion or fatigue.
However one biggest drawback of the headphone is that it makes you devoid of the other sound that emanates because of running, like breathing and foot-strike. You are unable to judge the amount and extent of your running. With the headphone in your ears, you seemed to be lost in another world of your own, whereby you are not able to hear any sound too around you, not even the horn of a vehicle. Obviously while racing too, you may not judge the directions of officials.
It is also true that music is not effective for the people who are 'associators'. Associators means athletes who concentrate more on their heart rate, breathing and muscular tension during running, and naturally music may not be of great benefit to them.
Music can naturally give you complete delightful feeling, With the music you enjoy your task more and feel like being yourself and have a complete holistic experience. You may feel running like boring but you can make it interesting and appealing by listening to the music. It may also be true that running with music on treadmill can obviously be better choice as compared to road running, as there are no distractions, and less boredom. But here too, much use of headphones can prevent you from hearing your footfalls and breathing. In short whether you are using headphones for running outside or on treadmill, effects are the same.
It is also a matter of one's taste and capability. Many runners can run for quite a prolonged period without use of any headphone because they love running, but some run just for their exercise and workout and for them earphones appear as a boon. Even though they are not runners, but when they have their earphones on their ears, they do not feel themselves less than any professional runners.
This is a magic of this small yet powerful headphones.