High intensity does border on leading to injury

Where are you getting this? The study was about various intensities of cardio - I didn't see it noted, but I'm guessing the high- and medium-intensity groups were on a treadmill, elliptical, or similar. Pretty small chance of injury for the durations they mention, especially as the subjects were monitored while exercising.

And I'm not really surprised by the study - building lean muscle mass takes resistance training, which wasn't part of the study. The study results appear to be inline with what was common knowledge/experience.

And if you're injuring yourself regularly during weight training or other gym activities, I'd suggest you might hire a good coach/trainer for guidance and programming, because that shouldn't happen either.