Flexion extension frequency and static vs active

 The fundamentals course has taught me that I have massive shoulder mobility issues. Especially relating to shoulder extension behind the back

two questions:

1)  i've noticed that many of these exercises instructed us to perform active stretches by moving our limbs.  Would it be bad to do an extension and hold it? 

2)  would it be bad to have a friend help me stretch further? These two exercises in particular instruct us to use our own muscles and doesn't say anything about having someone stretch us further. 

Sorry if that's hard to understand

Like most adults, we all have mobility issues. Holding the crab position is a form a static stretch. And in the next courses Coach Sommer will have exercises that will improve your shoulder extensions. I don't see any issues with some light partner stretching, just make sure the person that is getting the stretch is in control to the tension. Always play on the safe side. 

Got it. So, the mobility work we do in the fundamentals course will continue in the next courses? Or will I need to continue doing the fundamentals exercises in addition to the work in additional courses I subscribe to?