Mark Sisson follows up his essay reading last week with an engaging discussion with host Brad Kearns about the dangers of chronic cardio, and some tips to help avoid the drawbacks of chronic exercise patterns. Brad and Mark discuss numerous real-life case studies of elite athletes in endurance sports such as ironman triathlon and long distance running, who have suffered serious heart problems. Mark and Brad mention the tragic deaths of multi-sport athlete Steve Larsen at age 39 (heart attack while running), and Ryan Shay (heart attack while racing the US Olympic trials marathon), along with an assortment of other high profile athletes and their ordeals. Mark presents a compelling solution in essay form, pulling highlights from some popular follow-up blog posts on the subject. Mark mentions eating Primally, downscaling the "filler" workouts that happen between challenging "breakthrough" sessions, and realizing that interval and sprint workouts can deliver a training effect superior to long-duration workouts, while also alleviating the risks of drifting into a chronic pattern. For a good takeaway sound bite, Mark reiterates a message from a popular post about burning a total of only around 4,000 calories per week during structured exercise sessions. This is a general rule of thumb that correlates with an impressive assortment of different types of workouts that develop broad-based functional fitness, and helps protect against the excesses of chronic exercise.