This article like class, talks about heart rate reserve. It covers how to calculate it and what I found interesting and useful about it, also tells you what heart rate zone you should be working out depending on what you're trying to achieve. As an example, it talks about how working at 80-90% or the anaerobic zone, "will help to improve your body's ability to deal with lactic acid. It may also help to increase your lactate threshold."Overall, it's a great read for someone wanting to know more about heart rate reserve.