@CFS_for_19_years thanks for the tag. I do have an opinion, but it may not be what some expect.
@sharks the challenge with "exercise prescription" is that there are many factors to consider especially when you are looking at someone with ME or POTS. Most exercise guidelines (target HR, Level of resistance, number of reps, duration) are all established based on "norms" or averages of averages. Since there is no "average" person out there, any recommendation for activity or exercise should be based on that specific person (scientifically speaking N=1)
ME and POTS present unique issues most people are not even aware of. Most do not understand the impact or the potential magnitude PEM plays. What might be considered exertion for one person, might not be for another. Also it should also be based on what specific issue(s) the person is experiencing (muscle stiffness, joint stiffness, muscle weakness, muscle imbalance, lack of endurance, balance issues, vestibular problems, etc...).
For someone with ME, monitoring the level of activity and response to it is critical to attempt to avoid PEM or other negative responses. For most, as normal of activity as can be tolerated (without significant negative consequences) would be ideal. That might well mean no specific exercise is warranted. Just normal activity.
For "muscle stiffness" a gentle slow easy stretching program may be beneficial. Should not bounce, but should also not be sustained for longer than a few seconds either (believe it or not this can cut off blood to nerves or create weakness in muscles). Take plenty of time to perform so as to not add stress. Performing it in a comfortable and most restful position sounds right. If by doing this you are able to achieve an improved and sustainable level of activity then what you are doing could be considered successful.
You can't strengthen a muscle that's already in a contracted state.
Agree 100%. Mobility first. Strength second always in my book.