Typically, when we're looking for music to put on an 'exercise playlist', we'll choose modern music with a solid, steady beat. After all, the Moonlight Sonata wouldn't be motivational for a power walk, much less a jog.
Classical music is for relaxation. It's music to read to, music to send you off to sleep, to unwind, or to meditate. At a push, you might use classical music to exercise if your chosen exercise is yoga or Piilates. But for a run, lifting weights or a few rounds of gym equipment, you need something with a bit of oomph. So, that's classical music out, right? Wrong.