No doubt I have also this weird thing, not able to move quickly. It acts as if the muscle was suddenly stucked. Only doing slow movement is the rule for me. I may increase the duration of the movement/effort (...and then will face PENE), but in no way can I do the same with speed. I noticed it is not even related to increase of cardiac rythm. It feels like speed drives some disorientation to the brain, and muscles will be like "shocked" and petrified. of course this is no science, just the way I feel my body.