In the USA is is the law. Medical issues are private matters between a healthcare provider and patient. If a person's private information was to "get out" it might affect their ability to get a job or they might face other predjudices Also the private insurance numbers could be used to steal someone's identity.
I don't get the last one, so I'll give you the first 2.
COmmuicate:
1. Ask the problem: make sure to listen
2. Show you care about them: give them a reason to live
Offer Help:
1. Tell them that if they need anything, you will be there to help/
2. Get them a Psychiatrist, and tell them they will help
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If you can exercise without fatigue you are fit and healthy :)
To set your intensity level, you need to use your maximum heart rate, which is determined by subtracting age from 220.