iOS: Syncing your music's beats per minute (BPM) to your heart rate energises your workout, especially if you're doing interval training. RockMyRun reads data from a Bluetooth heart rate monitor and adjusts the music to match.
The "MyBeat" function in RockMyRun is currently just for iOS. Once you sync your heart rate monitor, the app shows your current heart rate. As your heart rate increases, the tempo of your music increases. You can select an initial BPM range when picking your music, too. Basic mixes are free, and there's an ad-free premium option that gives you more mixes and longer workouts.
You'll need to either download the mix in advance or use Wi-Fi to sync your heart rate to the music. The MyBeat function doesn't work over cellular connections.
RockMyRun [Google Play]
RockMyRun [iTunes App Store]