Start weight training
Start a weight training routine of four to six exercises for three to five days every week. A good weight-training regime includes squats, bicep curls, triceps curls and bench presses. Several variations of each exercise are available, however, consulting a physician to put together a comprehensive strength-training routine for weight gain based on what you is available to you would serve you best.
The Basic Crunch
Lie flat on the floor on your back with your knees bent and your feet flat on the floor. Put your hands behind your head to support it. Now, lift your shoulders a few inches off the floor with only your ab muscles. Keep your upper body up for 3 seconds and lie back on the floor. Do about 10-12 of these crunches.