If it were easy to stay motivated to work out, then we’d all have rock-hard abs. Alas, the drive to get out of bed for an early morning sweat session is elusive, except for those infectiously positive and perky fitness trainers and instructorsor so you thought. Even they need some encouragement once in a while. We asked four inspiring exercise experts to share what motivates them both in and out of the gym and studio. Their advice could be the extra nudge you need.