If you concentrate on the arms and legs at the expense of core muscles of the abdominals, not only will you look a little flabby, but you won't function well either. Here is how to get serious about core exercises.
The Abdominal Muscles
The 'abs' are the muscles in the abdomen or the stomach region-- generally below the rib cage toward the pelvis and at the sides. The three main groups are:
Rectus abdominis (RA)
The RA flexes the lumbar spine and tilts the pelvis and helps maintain curvature of the lower spine. It is commonly known as the six-pack because with strong muscle development and low body fat these muscles stand out.
Transversus abdominis (TA)
This is a deep layer of muscle supporting the internal structure and organs of the abdomen. It helps flatten the stomach, is used in forced breathing out, and in urination, defecation and childbirth.
The internal (IO) and external obliques (EO)
The internal and external obliques run down the side of the abdomen and help you bend and rotate at the sides and assist in trunk flexion. The external oblique muscles can be made to show through to some extent with exercise development and a low body fat percentage.
Consider four layers of muscle from the external obliques on the outside and to the sides, then the internal obliques followed by the rectus abdominis on the surface and then the transversus abdominis at the deepest level wrapping the abdominal cavity from back to front.
Regular attention to the abdominal muscles not only provides you with a nice looking six-pack, but it provides powerful functionality for most sports. Check out these serious exercises to get those muscles hard and strong -- and more.
The bridge exercise has you on the floor facing up, knees bent, butt pushed in the air and with hands on the floor for support. You perform the exercise by pushing up from the floor until your abs are slightly curved. Hold for 20 seconds or longer, then lower to the floor. Hits the butt (gluteus) and hamstrings as well as the abdominals. Do one set of ten.
Planks position you on the floor facing down and then pushing up so that you balance on the tips of the toes and extended arms while holding the body horizontal. Brace the abdominals. If you can hold for two minutes you are doing well; for three minutes, excellent. Do three sets of 1-3 minutes, one minute rest in between.
You need a rollout wheel, which is a small wheel with bars on each side. For this one you are on your knees on the floor. You bend over and push the wheel outward from the body until you are more or less in the plank position balancing on the toes, abs braced and held firm with the body horizontal to the floor.
Number one is the bicycling crunch. Lying face up on the floor, assume the crunch position with shoulders raised from the floor, but now raise the legs to the point where you can rotate them as you would if cycling. Keep those abs braced and feel the burn. Cycle for twenty seconds. Do one set of ten.
Number two is the combo crunch. With standard starting position for the crunch, you raise the knees from the floor and cross the ankles while bracing the abdominals. Hold for fifteen seconds. Do one set of ten.