So a few important things to emphasise, a lot of the studies into Z2 being more beneficial have a myriad of factors that mean those studies aren’t necessarily applicable to recreational athletes. Firstly, zone 2 is needed for professionals training a large volume as they can accumulate more training stress without the fatigue of intervals and get benefits that are required to those competing in longer multi-day events.
Secondly, zone 2 conducted as x5 1hour sessions is not as beneficial as x2 2.5 or x1 5hour session as several of the key benefits come from the actual duration and repeated muscle contractions of Zone 2 rides. In that scenario, 1 hour of intervals will be better for aerobic endurance than 1 hour of Zone 2
Thirdly, it depends on the population. Zone 2 equivalent exercise is generally better for those who do not exercise as much and want to do it purely for health. Higher intensities are really tough if you are not used to them, so maintaining a plan is difficult and fatigue from the session if it’s HIIT can be too much.
I’ve tried and tested a lot on myself. I was my fittest when I was doing 26-30 hours of riding a week, with around x4 6hour Z2 rides with efforts in the final hour to simulate end of race efforts. I also did x2 e races a week for the very high intensity. This was after uni, mid-pandemic, with not work. Now, I work full time and don’t race. I have no time for lots of Zone 2, and had been doing x4 1-2 hours Z2 a week. Fitness went nowhere. Now I’ve added x2 1 hour intervals a week and aerobic fitness has improved a lot more. I still only train 4-7 hours a week, but HIIT has been essential for me.
So for the majority of users on plans on SYSTM, the current pyramidal structure will be the most appropriate for them and also the best plan to maintain alongside work and family. It’s hard to make enough off-the-shelf plans to fit every single possible time structure that SYSTM users have. So my advice would be to use the sessions during the week, and weekend if time is short, but if you have time maybe do 1-2 longer Z2 rides at the weekend, while doing key interval work during the week