This is called "polarized training". Dr Stephen Seiler is the most well-known researcher investigating this and has done many lectures and interviews with endur

This is called "polarized training". Dr Stephen Seiler is the most well-known researcher investigating this and has done many lectures and interviews with endurance sport Youtubers and podascters about this -- just search for his name on Youtube. The research shows that lots of exercise volume at low intensity, a bit of excersise volume at high intensity, and zero volume at mid intensities is (counterintuitively) the most effective way to build performance at all intensities for endurance sports. This applies both for trained professional athletes and regular people who are untrained. In some of the videos you'll find, he provides definitions for these zones and makes suggestions about the ideal volume of exercise, as well as the structure of high intensity workouts (how many intervals? how long? etc -- there is research about exactly what intervals are best) If you are interested in improving cycling performance, https://intervals.icu/ https://intervals.icu/ is a fantastic dashboard that can be used to track training, performance and has many charts directly relating to polarised training and Dr Seiler's research (I'm thinking specifically of charts for time-in-zone, cardiac decoupling and heart rate reserve) There are many cycling training Youtubers but Dylan Johnson is one who comes to mind who looks takes a very evidence-based approach and breaks down the latest research in videos for beginners who want to improve cycling performance