Max Heart Rate and Training Zones This is no medical advice. Although moderate to strenuous workouts are generally considered healthy, everything depends on you and your situation. A trial1 at the Mayo Clinic with middle-aged, obese participants concluded that higher intensity workouts have the highest chance of increasing cardiorespiratory fitness while still being medically safe. Nevertheless, if you think you are not healthy, see a doctor. If you are over 40 years old and have not worked out in the last couple of years, go see a doctor before starting a new fitness regime.