Why are there HIIT sessions in my base phase?

I get this question a fair bit so I’m adding it here to the forum. While there are stories of periodization where athletes have exclusively performed low intensity high volume in the base phase leading to successful outcome, we generally take a more balanced approach to training in line with Rønnestad et al. (2014) where they showed that performance in the following year is better when a small amount of HIIT is included in the base phases. Thus, you’ll note that there is typically only 1 session in the week that hits this target. But (we feel) this is still an important day for you to touch on the high intensity stimulus and to remind the larger muscle fibres and heart that it will need to engage in such high intensity activity in the future…


And they are fun. this time of year when most of the sessions for me need to be done indoors having session variance is important. Most modern preventative cardiologists say VO2 max is one the best variables to indicate life expectancy so it’s great to see these sessions even in the base phase.