Nice and simple- steroids increase muscle size, strength yada yada yada.. but not tendons, ligaments etc as quickly... so? Muscles get big and strong, very fast, but the tendons, ligaments yada yada don't as quickly... therefore, people on steroids, are more prone to muscle tears and tears of the supporting structures which attach muscle to bone etc. this is the simplified 3rd grader explanation, that hopefully even you can understand.
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