This workout uses the hollow-body rock—a classic gymnastics position that is great for strengthening the core—and takes it to the next level.
Adding a single dumbbell increases resistance, and therefore strengthens the trunk more than a traditional hollow rock.
Since the added weight is only on one side, your abs must fight rotation in order to stabilize.
"This carries over to life and sports where you are constantly fighting a greater force on one side of your body verses the other," says Andy Speer, creator of The Anarchy Abs Workout from Men's Health.
It also prevents cheating by taking your legs and hips out of the shoulder press, Speer adds.
The pyramid rep scheme, in which each set builds in reps and then works back down, encourages a higher overall volume of reps without reaching failure.
Stopping before reaching the extreme muscular fatigue of technical failure will help you maintain perfect form.
Start by holding the weight with your left hand. Perform 1 rep of the hollow body rock to L-sit press, then 2, then 3, and so forth until you reach 5 total reps.
Transfer the weight to your other hand. Start with 5 total reps. Work your way back down, subtracting 1 rep each subsequent set until you are down to 1 rep.
That's one round. Do 3 to 5 rounds as a finisher for core and upper body. Rest 30 seconds between rounds.