This is an example of intensity change because he is deciding in one moment to add stretching his arms over his head to each set and it is referring to extreme strength, force, and energy.
He is adding more because he wants to make the transformation and strengthen his muscles. The person who is doing exercises can measure his intensity with heart rate and age.
All of these do seem like possible injuries that could happen in sports the answer that makes the most sense to me is B since it seems like getting arthritis from sports injuries does not seem that common,
