Some exercises for achieving a flat stomach include the pike and extend, the plank and the squat. These exercises tighten the abdominal muscles and work the adjoining thigh, chest and arm muscle groups.
In the pike and extend, lie face up, lift your legs above your hips, crunch forward and reach so that your fingers touch your feet. Hold for a few seconds and slowly lower your legs and hands back to position on the floor. Do 20 repetitions.
In the plank, start by kneeling on all fours, then slowly lift your knees off the floor so you are in the 'up position' of a push-up. Hold for 1 to 2 minutes while keeping your body long and straight.
In the squat, keep your feet apart and bend your knees as if you are sitting in an imaginary chair, keeping your spine straight as you do this. Repeat 10 times. Increase the level of workout by holding weights to your chest or back.