You may have seen Don Brooks on an episode of KUWTK, taking the Kardashian sisters through one of his intense workouts. (He also works with Kanye West and Fergie.) Brooks created the Don-A-Matrix method, high-intensity intervals with strength-building moves. Follow him at @donamatrixtraining, then try some of the arm moves he uses with Kourtney and Khloé Kardashian.
Photo: Instagram @donamatrixtraining