Paul Williams, a runner who completed a marathon in 1988, is more importantly a scientist at Lawrence Berkeley National Laboratory, and has been conducting a study on exercise for the past 20 years! His conclusion? More is always better! He focused his study mostly on runner's because we generally have a better documentation of our exercise schedule and it's results (races!). He's been a critic of the national guidelines advising Americans to get "at least" 30 minutes of exercise per day. His study revealed that while "at least" 30 minutes is good, more is still better. Read the FULL ARTICLE.