If you want a flat stomach, know this: No amount of crunches or flat-stomach exercises will magically get you there.
That said, these effective flat stomach exercises from Patrick Goudeau, a trainer and studio. manager for Life Time Fitness, work because, yes, they're core moves, but they also recruit other muscles to increase your overall effort level—which burns more calories and will build more muscle elsewhere in your body. The moves are perfect for tacking onto the end of your cardio or strength workout or squeeze in at home when you don't have time to hit the gym. (And, FTR, core strength has a lot of benefits besides helping you get a flat stomach!)
How it works: Do each exercise in order for the indicated number of reps with little to no rest between moves. The complete circuit should take less than 10 minutes. Pair it with one (or a few!) of these best at-home workouts to customize a longer circuit.
You'll need: a medicine ball (optional)