I wish we could see what your reference was. But stiff isn't exactly the word I would use. It looks without motion. It looks like our man is tired, tried to lift himself onto that ledge, then rested into place. If that is the intent, then it works. But if he is in motion, it is missing that movement in the body. This is typically shown by a stretching in the muscles as they push on the body, curves, bends and twists on the joints. His back is hunched, but if someone were lifting themselves onto a ledge, there would be an arch either in the abdomen, or his back.
