Read this article which I thought was interesting with comparing volume and intensity focus for cross country skiing. Cross-country skiing: high intensity training results in increased VO2 max levels | Peak PerformanceGranted this article focuses on VO2 Max which improves from training VO2 Max. I have been shifting my training to include more low intensity training to follow more of the 80/20 principles for the purpose of improving recovery from high volume of high intensity. However, perhaps 80/20 isn't the primary takeaway and just training the ends of the spectrum are more important than the ratio of one to the other. What are some other studies that compare volume and intensity focus for endurance sports?