Does sprinting/HIIT help define build or add strength or your leg muscles?
I would recommend just regular running, rather than sprinting. You will get a better workout because you will last longer.
sprinting and HIIT are very different.Sprinting is anaerobic, whereas HIIT is aerobic. If you want to add strength/size to your legs, sprinting would be more beneficial than HIIT.
The reason why HIIT works the way it does is it breaks down muscles like lifting does. HIIT is anaerobic as well. If you can manage HIIT while doing a squat at the same time, you'll get twice the benefit. Don't squat more than what you can balance or you might tip over.
SQUAIITZ