Total frequency and volume
No matter what endurance sport you look at, the very best competitors usually undertake large volumes of training. This will differ by sport, with non-impact sports like cycling and rowing generally recording higher volumes than impact sports like running, but the correlations are very consistent no matter the sport. In short, more is more here but how much training an athlete can manage is where the coaching comes in. Ensuring an adequate progression depending on the age, experience and ability of the rider as well as managing the intensity distribution of their training is vital to ensure they stay illness and injury free and achieve (my favourite word) CONSISTENCY.
High intensity intervals
Many studies over the years have established the effects of high intensity interval training on endurance performance. Usually, these are targeted to improve lactate threshold or VO₂max, measured in a lab, or time trial performance. Interestingly, protocols ranging from 30s all out efforts (Burgomaster et al., 1985), or more traditional longer intervals have both been found to be effective in improving 40km time trial performance in well trained cyclists (Laursen et al., 2005). Different interval protocols can be used to target your goal events or adaptations desired but these are the second well proven layer of the endurance performance pyramid.
Training intensity distribution
If the foundation of the endurance training pyramid can be summarised as 'ride more', training intensity distribution takes this a step further, examining the make up of all those hours of training over an athlete's career. Again, over a variety of sports, top cyclists, runners and rowers tend to follow a polarised training distribution, with roughly 80% of their training at lower intensities (think your traditional Zone 2 base miles), a relatively small amount of training in what we usually call zone 3 and the remainder as high intensity interval training in zone 4+.
