Wait a minute, the part about injury/death is a bit ridiculous. With this logic, stay sedentary, no risk of injury/death from training ever, that's for sure. An

Wait a minute, the part about injury/death is a bit ridiculous. With this logic, stay sedentary, no risk of injury/death from training ever, that's for sure. And never ever go to the mountains or dive! I do HIIT, with running uphill on treadmill (1 min sprint, 2 mins slow pace, increase inclination, repeat), but it's only one type of running I do (others are slowly increasing speed and inclination every 5 mins, and just circles in hilly park nearby). It's very effective, 'different' type than others (heart rate takes very long to come down for example). Definitely I feel my knees more after usual running on concrete in proper shoes rather than these treadmill sprints. If you don't challenge your body and put some pressure on muscles/joints/ligaments/cardiovascular system etc. it will never reach its potential. Would I do this if 60 years old? No. But I don't consider such blank statements true. If you don't want to do HIIT for whatever reason, that's your choice