As Chris Hemsworth explained, his trainer introduced him to blood restriction training, which forces certain muscles to work while cutting off others and makes the workout difficult -- even with “light” weight. As you can see, the Marvel star immediately felt the difference doing four sets of bicep curls then hanging on a rope to burn his arms. Hemsworth is, of course, very charming and hilarious throughout, but he is clearly going through it. Still, the results speak for themselves.