abdominal muscles

The abdominal muscles—rectus abdomenus and the internal and external obliques—are part
of the group that form the trunk musculature Weak abdominal muscles are a cause of bad posture
and may be a predisposing factor in chronic lower back pain. Strengthening these muscles
will firm the waistline, improve posture, and result in a trimmer appearance  However, abdominal
exercises do not spot-reduce fat from around the abdomen and waist . Fat is lost only by
expending more calories than are consumed.
The sit-up is one of the most common exercises for abdominal strengthening and toning.
The Bent-Leg Sit-up is popular because it does not cause excessive stress on the lower back.
Straight-Leg Sit-ups are not recommended and should be avoided because they may cause undue strain
on the lower back.(Straight-Leg Sit-ups work the hip flexor muscle as opposed to the abdominals)
authorities agree that (depending on the type of exercise) abdominal muscles, unlike most other muscle
groups, can be worked on a daily

basis. Weight-resistive abdominal exercises should usually be
alternated with a day of rest. Rate of progress is an individual
judgment, but in the beginning it is best to proceed slowly.
Abdominal exercises may be used for fully defined muscular
development or as a warm-up routine for other exercises and
sports. In a muscular development routine, abdominal muscles are
strengthened by:

1.increasing the number of repetitions per set
2.increasing the number of sets
3.progressively shortening the rest periods be-tween sets
4.increasing the angle of the exercise
5.strapping on leg weights for some exercises or holding a weight plate
 while performing other exercises.
Abdominal exercises are usually performed with higher repetitions per
 set than are most weight-training exercises.