Most of what I read points out that it's more likely to happen to untrained individuals. It may be because they start to hard over multiple days, but that's not going against what I've said multiple times: that it's a high risk for untrained individuals jumping into high intensity training. _That's_ my point.
This statement erases all nuance in the real world data and experience of anyone involved in training.
You need to differentiate between one HIIT session and repeated HIIT sessions without recovery. The former doesn't cause injury in the vast majority of individuals. The latter is known to cause injuries in everyone trained or untrained.
You also need to control for what the HIIT session is. If it's spinning on a stationary bike for 2 minutes, an untrained individual generates nowhere near enough force to then injure themselves. If you're putting a set weight on a bar and asking them to shoulder press it, that's self-evidently completely different.
Yet, in your argument, they're exactly the same.
- This wasn't one group session but repeated sessions of HIIT back to back (maybe even daily).
- There wasn't sufficient rest between sessions.
- Some of these were older (50+) patients.
The most important part is the repeated sessions. Doing a single session of HIIT pull-ups or sprint intervals on the bike aren't going to cause major muscle damage, even in an untrained person. Doing 5 days back-to-back, repeatedly going beyond failure (something Crossfit is notorious for), with improper form, are what causes the issue.