When you're running at a consistent pace, you can focus both on song lyrics and the activity, says David Siik, LA-based senior manager of running for Equinox and creator of Precision Run. But if you throw intervals into the mix, your brain becomes overstimulated.
“Keep the beat but take away the lyrics and you reduce the noise,” Siik explains. “This allows your limbic system, which is responsible for behavior and motivation, to light up.”
Instrumental tracks also allow you to invest early in your technique, the muscle memory of your stride, and the rhythm of your run, says Curtis Longfellow, studio manager and coach at Precision Run in New York City. "Once you have that form locked in, you can cut loose and let your favorite songs push you to the finish."
The bottom line:
For interval workouts, build playlists that contain non-lyrical music for the first third and your favorite running tracks for the rest, Siik says. Keep the beats per minute consistent throughout.