The hundred is an excellent stomach exercise for developing torso stability and abdominal strength. It is also known as a hundred seconds of pain for obvious reasons as well. It is very important to hold your neck correctly because the exercise is more effective if your head is kept high, this also prevents neck strain. If any neck strain is felt the exercise should be stopped immediately.
Lie on your back with knees bent and feet in the air, shins should be parallel to the floor and hips just apart a little. Push your inner thighs slightly together.
While inhaling, reach your arms straight up with palms forward.
Exhale and lower your arms back to the floor while straightening your legs in the air and slowly rolling your torso up remembering to keep your neck tucked in to your chest with a gap of about a tennis ball.
Leave your legs in that position and while inhaling return your arms to the starting position. Repeat this 10 times.
Each inhale and exhale should last about 5 seconds so this exercise will take 100 seconds, hence the name. The final position should be with shoulder blades slightly off the floor.