Typically, cutting off your own blood flow isn’t an awesome idea, especially if you are exerting more energy and effort than normal – you know, like during a workout. In fact, Chris Hemsworth seems like he is in a significant amount of pain while lifting a relatively small (for someone like Hemsworth, anyway) set of weights while wearing the occlusion bands on his arms. After he is finished with his set and moving on to a different, but one that would be equally mild without the bands, exercise Hemsworth can be heard expressing his apprehension to the method, and later even saying he feels sick.
