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I also primarily do a lot of weight lifting. Its difficult not having the Apple Watch bumping into things with the weights, but I would suggest you could purchase a bumper that surrounds the Apple Watch casing to help protect it.




“If you sell or give away your Apple device, you can also transfer the ownership of your AppleCare Protection Plan or AppleCare+ in regions that allow it. You can also transfer your AppleCare coverage plan between your own devices that are the same type of product and within 30 days of your original device purchase. “

https://support.apple.com/en-us/HT202712
Yes, I have transferred AppleCare on several different devices I purchased secondhand: AppleWatch Series 2, iPad Pro 12.9, worked beautifully.
 
I also primarily do a lot of weight lifting. Its difficult not having the Apple Watch bumping into things with the weights, but I would suggest you could purchase a bumper that surrounds the Apple Watch casing to help protect it.

Twelve South sells an armband for the watch. Some people have given it bad reviews for durability. I have one but have only used it a handful of times. Overall it works well to keep the watch out of harm's way during certain activities.
 
So I sold my Series 1 on Swappa. WOOHOOO!!!™ Just purchased a refurbished Series 3 (GPS) on Apple.com that will arrive Friday. WOOT!!
 
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