MyGroupFit is a great resource specifically for fitness instructors. Not only does the site consists of music mixes, but clips of exercise moves you can use in your classes, and health and fitness-based educational articles.
The music mixes aren't free, but they are good! You can download a digital copy of each mix for $18.79 or purchase the CD version for $19.95. The site makes it easy to find a mix based on genre, tempo or class type.
Recently, MyGroupFit added an app (both for Apple and Android products) where all your purchased mixes can be viewed, and a subscription service is also available. While you'll have all of these mixes in one place, the drawback is that you can't modify the tempo with a tempo app such as Tempo Magic or Audipo.
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