It's funny - I guess it's a Medium thing. I see the majority of comments are from people seeking to fight with the author.

I'd say, if you're over 40 (or 77, as one of the commenters is) and you're TRULY doing HIIT at exactly the level the author describes as valid HIIT, and you're doing well, great. Why pick a fight?

At 67, I took a 40 minute HIIT class and loved it. I had personal training sessions in which the trainer pushed me even harder, and I loved it.

Just after my 71st birthday, my blood pressure, which had been relatively well controlled since my late 50s, (around 125/85) started inching toward 160/100 - the meds I had relied on for 13 years just didn't work any more.

I won't bore you with the details - the meds were adjusted, I'm back to where i was - but boy, I started doing high rep/low weight workouts (like, from 35 to 45 pounds to, yes, 8 pounds).

relax folks. If it works for you, great. I think this was a very well written article, and since 80% of the population doesn't do ANY exercise (other than a few 20 minute walks a week), any article that helps prevent a large number of people from giving up altogether is just fine, as far as I can see.