As athletes, most of us have been exposed to two forms of pain. The first is physiological and comes from the neurological responses sustained from musculoskeletal injuries. The second form of pain is much more insidious. It creeps up on you in the midst of an intense workout, smothering you until you feel you can no longer breathe. Unlike a torn ligament or pulled muscle, where rest is beneficial, rest only makes this second form of pain persistent and more debilitating. Giving into it makes you less fit in the long run. By now you should be aware that what I'm describing is the pain associated with fatigue -- the heavy arms, the uneasy stomach, the feeling that your lungs are getting smaller as each minute passes. If your diet is clean, you're getting adequate rest, and your mechanics are solid, then intensity is the next step toward improving your fitness. The fittest individuals in our box have learned how to cope with, and even embrace, fatigue. Ask them what makes them push so hard. Each one will have his or her own interesting and unique answer.