Mel Siff Quote

“To me, the sign of a really excellent routine is one which places great demands on the athlete, yet produces progressive long-term improvement without soreness, injury or the athlete ever feeling thoroughly depleted. Any fool can create a program that is so demanding that it would virtually kill the toughest marine or hardiest of elite athletes, but not any fool can create a tough program that produces progress without unnecessary pain.”
Dr. Mel C. Siff

This quote has tremendously influenced my training philosophy.  Progress while avoiding injury should be main goal, not just getting all sweaty and tired with no progress.  If you want to get sweaty and tired do jumping jacks for a couple of hours.