Depends on your reasons for doing it I'd think. There is an "exercise addiction" where you exercise to the point where it's obsessive, and you do it until you're in pain... but it could also be self-injurious. Anything in excess can be an injury, therefore self-injury.
Self-injury is basically the intent to cause harm to yourself... if you're only in it to feel pain, then I'd say yes, it could qualify as self-injury.
Can you cut back on your exercise, or find some other way to get rid of your extra energy that wouldn't result in physical pain?
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