My impression is that those folks were of the medal contender variety. Be that as it may, I tried that interval protocol in my late 50s. It was extremely effective, but also a very large training load for me, so large that just doing one set/week in addition to my weekly hard group ride had me overtrained in a month way back then. So I quit doing that. YMMV. I was killing it for that month though! Then one day I realized as I was riding uphill to the gym for a workout that I was grabbing a smaller gear rather than a larger. Uh oh.

If you can just barely hold that effort level for 8 minutes, you're doing it right. You should be panting hard all the way after the first minute. It takes a little practice to learn how to titrate the pain. And it's all about recovery.

In my case, the social aspects of the group rides were more important to me so I dropped the intervals. If I were training seriously, I would have done the opposite.