a calisthenics lying triceps extensions tutorial. a) Set up in a plank position with your elbows slightly more forward than standard and your back straight. b) Engage your core and retract your shoulder blades. Your head should be directly above your hands. ACTION: a) Contract your triceps to push your body off the ground and slightly back. b) Squeeze your triceps hard at the top of the rep and slowly return to the starting position. c) Repeat this motion for your desired number of reps.