Can you hurt yourself jerking-off i.e torn tendents

There is no such thing as a "tendent."

You can hurt yourself if you do it too hard. Also issues at times if you do it too often

Sure, you could get carpal tunnel syndrome.

With any sport or activity that exercises joints there is a possibility of injury. I would just cover up before you call for the medic. :-)

There is also the problem of friction if you don't use enough lube or lotion. This could result in dry and splitting foreskin. If you're circumcised than you don't need to worry about that but the need for lube becomes more dire. I am not circumcised so I am not sure what that feels like.

Lastly you might want to check your grip while masturbating. If you are choking your chicken far too hard than you might be conditioning your penis for a certain style of stimulation. When you get with a woman, it could cause you to lose your erection and a disappointing night. You shouldn't really have your thumb pass any of your fingers while you're beating your meat.

@J_9, it is more of a elbow exercise for me. TMI I know, but still...