Fitness

There's a couple of things to be said.

1. The evidence for most exercise programs is pretty flimsy. They all have problems with sample size -it's hard to find people that will take up exercise that haven't been already doing it, and here the evidence shows that it works about as well as you would expect another effective exercise program to do, rather than better.

2. It's not HIIT. There's no real on and off, it's just 7 minutes of fairly consistent intensity. It's also not that intense compared to say playing sport as a hobby. If you're worried about injuries, you want probably want to avoid impacting movements, and ballistic movement, and there's very little of that here. Probably the worst bit is the jumping jacks, which are still likely to be lower impact than going for a run.