Hellow,Sir:
1.FitSDKRelease_20.88.00\cs\Examples\Encode\EncodeDemo.cs   to build "ExampleActivity.fit" ,but 
https://app.trainingpeaks.com/#calendar can not Read this fit. I used Framework 4.5 
2.In folder 
Downloads\FitSDKRelease_20.88.00\examples\Activity.fit can read by 
https://app.trainingpeaks.com/#calendar 
Can you Share .net  Sample Code to me ,Let ME Know How to encode the sample Activity.fit