Not sure that there really is a 'legal' way to download music without paying for it. Unless you go to bandcamp and an artist has a pay what you want that starts at $0. http://bythebirch.bandcamp.com/releases
The right tunes can motivate you to upgrade your workout from just ok to great. If you are looking for ideas for motivating pop workout music, I’ve got you covered. Here are my favorite pop songs from 2015!