Everyone from Peter Attia to the Global Cycling Network is talking about zone-based fitness training. It’s gaining popularity as a way to optimize your workouts and train like an endurance athlete, all while making sure you don’t work too hard. What is Zone 2 training, and how can you do it effectively— no matter your fitness level? Dr. Stephen Seiler is a professor at Norway’s University of Agder, and for decades he’s been researching the concept of the “polarized training” that separates training styles by lactate range and heart rate. Here, he explores the benefits of slowing down with Medcan CEO Shaun Francis.