When most people think of ab training, they think of crunches — and for good reason. Done correctly, crunch variations are still one of the best ways to build core strength and definition. In this crunch HIIT workout , you’ll combine three crunch-based moves into a fast-paced 10-minute circuit that hits your abs from multiple angles. The Workout Format: 30 seconds each move 15 seconds rest between moves 3 rounds total Rest 1 minute between rounds Moves: Crunch Reverse Crunch