I have been using trainerroad for the last few weeks and have been enjoying it so far. I like that the workouts are set for me, and it takes a lot of the guesswork out of training. I’ve also noticed that each week the workouts are very similar, but a little bit different, ie a certain workout will always resemble 3x 15 minute at 90% FTP intervals, but have different variation in power across the interval. For example take a look at the “Tallac” workout, rather than setting the whole 15 minute intervals at 90% FTP, there are seemingly random fluctuations across the 15 minutes between 88-94%. Alternatively some other interval sessions like Leconte will be similar except for 30 second 105-110% spikes.
I think there is sufficient evidence (peer reviewed studies) that repeated intervals of any length/intensity are effective for improvements in different areas. With that in mind, are these differences between the workouts designed to keep users from getting bored of doing the same 3x15 minute workouts week in week out? Alternatively, do they actually lead to a more effective workout than intervals at a set %FTP? If there are studies which have been conducted to confirm this could you please share them. I am very interested in learning as much as much as possible on the topic.