Bodybuilders and athletes often fail to understand the specific muscular action and function of various muscles. Because of this they do not always use the best exercises or a sufficient number of different exercises to fully develop the muscles being worked. Thus , to improve your workouts, use anatomy and physiology in your workouts. Let them be your guide.
To illustrate, I will use the four abdominal muscles, three of which are used for movement. The most prominent muscle is the rectus abdominis which runs from the base of the rib cage to the pubic bone. It comprises the outer layer of the abdominal muscles and is involved mainly in flexion of the spine, i.e., raising the head and shoulders when the pelvic girdle is stationary or raising the pelvis when the upper trunk is stationary. In some cases you can find both the pelvis and shoulder girdle in motion at the same time.
The Upper Abs.
Because the rectus abdominis is involved in only flexion, you should do exercises that involve pure flexion. An example of this is the: 1) Sit-up. In the sit-up you raise your head and shoulders about 45 degrees off the floor. The axis of rotation is in the waist so that the lower back is no longer in full contact with the ground (as occurs in the crunch).
The sit-up exercise works mainly the upper portion of the rectus abdominis. It is important to understand that because of the length of the rectus abdominis most of the shortening takes place in the upper end. The lower end undergoes tension but does not experience the same shortening. As a result, the upper rectus abdominis gets most of the development.
2) To increase the difficulty of the sit-up you can do slant board sit-ups, or for even greater effectiveness Glute Ham sit-ups. When the sit-ups are done on the Yessis Glute Ham Back machine, you assume a seated position so that the buttocks are in contact with the seat when your feet are secured. You then lean back and go slightly below the horizontal so that you place the abdominals on stretch.
When a muscle is placed on stretch it can contract with greater force resulting in greater development through the full range of motion. However, you should not excessively arch the back and lower your head and shoulders too far. Go down approximately 20 degrees from the horizontal which is sufficient to create a very powerful stretch of the abdominals and then rise up to the seated position.
In this and other exercises similar to the sit-up, the hip flexors will also be involved, but this is necessary to stabilize the pelvic girdle to allow the trunk to rise up. This is the safe way to do the exercise. You should use other muscles to stabilize the adjacent joint to allow for movement at the joint needed.
Lower Abs.
To work the lower end, you should do an exercise such as the 1) Reverse Sit-up. In this exercise, you lie on your back and then raise the hips (with bent legs) up off the ground in a curling action toward the head. The lower end of the rectus undergoes most of the shortening, and thus it receives most of the development. If you raise the hips sufficiently high the entire rectus shortens.
2) Another exercise that is very effective for development of the lower abdominals is the hanging knee-up or hanging leg raise. To do these exercises, you should assume a hanging arm support position on a hip flexor machine or free hanging from a high bar. When your body is fully extended you then raise the knees as high as possible so that the pelvic girdle undergoes as much rotation as possible.
If you keep the knees bent you will have the greatest range of motion, and when you straighten the legs the resistance increases greatly. Because of this if you can raise the legs to the horizontal or slightly above, you will be getting very good development of the lower abdominals. Thus, some form of sit-up and reverse sit-up is the key to receiving full development of the rectus abdominis.
In regard to the crunch exercise it should be stressed here that this exercise involves flexion of the thoracic spine, not the lumbar spine which is the anatomically correct function of the rectus abdominis. In the crunch there is shortening of the upper fibers of the abdominals, but their action is to pull the rib cage down toward the hips rather than raising (curling) the entire upper trunk. As a result, you get shortening and tightening of the upper rectus, but you also develop round shoulders in the process. Because of this, for bodybuilders and athletes who need good posture and a healthy spine this exercise is contra-indicated.
The negative aspects of the crunch can be neutralized if you also do exercises such as the back raise or floor back arches. These exercises help return the natural curvature of the spine so that you do not become round shouldered.
It is also important from a functional standpoint that the crunch not be done too often. The reason for this is that you do not normally bend in the thoracic area. Doing this accentuates the thoracic curve which compresses the rib cage which in turn may make it more difficult for you to breath. The sit-up is much more effective since it uses an axis in the waist which is a more natural method of bending. However, keep in mind that if you are going to be lifting something heavy the rounded back is not recommended. In this case, you should maintain the spine in its normal slightly arched position and use the gluteus maximus and hamstring muscles to do the work.
In the sit-up and reverse sit-up, two other abdominal muscles are also involved; the internal and external oblique. The external oblique runs at a diagonal on both sides of the rectus abdominis and constitutes the second layer of abdominal muscle. When viewed from the front, the fibers depict a letter “V.”
The internal oblique lies directly under the external and forms the third layer of abdominal muscle. The fibers of the internal oblique run at 90 degrees to the external oblique at the upper end (in the area of the waist), and form an inverted letter “V” when viewed from the front. The fibers change angles as you move toward the hips and run fairly parallel close to the pubic bone. But because of the diagonal line of pull of the oblique muscles their main function is rotation of the spine.
However, in the sit-up or reverse sit-up as the rectus abdominis contracts the internals contract to rotate the shoulders in one direction, while the externals contract to rotate the shoulders in the opposite direction. The opposing muscle pull then becomes equalized and as a result, these muscles have a resultant force which assists in spinal flexion. However, be aware that flexion is not the main function of these muscles; it is rotation. Thus, to fully work the internal and external obliques you must do a twisting-type exercise such as the reverse trunk twist or the Russian twist.
1) In the reverse trunk twist, you lie on your back with the arms out to the side and the thighs perpendicular to the trunk. You then lower the legs to the left and to the right alternately. In this exercise, the pelvic girdle and legs are in motion. In the beginning stages of doing this exercise keep the thighs perpendicular to the trunk and the knees bent maximally so that you have a short lever. To make the exercise more difficult, straighten the legs or keep them slightly bent in the knees if you have tight hamstrings, and then lower the legs from side to side in a repetitive motion.
2) The Russian twist is a more advanced exercise which involves shoulder rotation through a full range of motion, while the legs and hips remain stationary. The exercise is typically done on a Back-Glute-Ham machine with the hips positioned on the seat when the legs are secured. You then lean back with the trunk until your body is in a straight line and horizontal. You raise the arms and hold a weight in the hands if greater resistance is needed. You then rotate the shoulders and the arms a full 90 degrees to one side and then up and over to the other side.
Beware of some of the more common exercises that involve twisting such as the sit-up or crunch with a twist. These exercises create tremendous shearing and compression forces on the spine and are a major cause of back injury. Keep in mind that when you do the sit-up or crunch the spine is flexed. In this situation, the vertebrae open up to the rear and compress on the anterior (inner) side.
As a result, the inner portion of the disc gets compressed maximally. If you then rotate the bones actually rub on the disc quite severely in what is known as a shearing action. If the pressure is sufficiently great it will result in a rupture. This can happen not only in the lumbar area which is involved in a sit-up, but also in the thoracic area which is involved in the crunch.
It is also important to understand that when you rotate (in the crunch or sit-up), it is impossible to go through a full range of motion if the spine is maximally flexed. Rotation occurs most effectively and safely when the spine in its basic or normally slightly arched position. This is why in the reverse trunk twist and Russian twist the spine is basically in its anatomically correct position, i.e., it is neither flexed nor hyper-extended.
It is also important to understand that twisting when the spine is flexed or hyper extended is the number one cause of back problems. When people who injure their back are questioned they invariably state that they were bending over and then twisted or they were reaching up in an arching action and then twisted. Thus, beware of any twisting actions when the spine is in a rounded or flexed position.
In addition, rotating the shoulders and then doing twisted sit-ups is equally dangerous for the same reasons. Thus when you do abdominal exercises the movements should be pure. You should not try doing more than one action at one time, as you will increase the potential for injury. In essence, either flex the spine or twist the spine, but do not do both at the same time.
Based on the above descriptions, you can see that it takes a minimum of three exercises to fully work the abdominal muscles involved in movement. This may explain why if you have only been doing sit-ups you do not get full abdominal development. This is especially true of many women. Some of them do hundreds of sit-ups daily, but yet they still have a pouch in the lower abdomen which they maintain is impossible to get rid of. However, by doing exercises such as the reverse sit-up and reverse trunk twist, they would find that all areas of the abdominals are effectively worked and they will see definite changes.
The fourth abdominal muscle is the transverse abdominis which forms the deepest layer of abdominal muscle. This muscle is not involved in movement and its main function is forced expiration. Thus, it is a breathing muscle. It should be noted here, however, that when you are executing forced exhalation the internal and external obliques also contract to assist in this phase of breathing.
In addition, the transverse abdominis plays a very important role when trying to force out body feces and women rely on this muscle greatly during childbirth. When this muscle contracts it fully squeezes in the abdominal wall which in turn helps push the fetus out the birth canal.
Without special equipment the transverse abdominis is fairly difficult to strengthen with overload, mainly because you can only breathe out so hard or fast. However, today there is a device called The Sports Breather, which allows you to increase the resistance in forced exhalation. In this way the transverse abdominis can more strongly contract to force the air out of the lungs.
Also, you can adjust the resistance for inhalation which helps to strengthen the diaphragm and the internal and external intercostals, which help to lift the ribs up to expand the chest cage when inhaling. The Sports Breather is a relatively small piece of equipment that you can carry with you to practice forced inhalation and exhalation throughout the day.
Studies have shown that not only do you get stronger muscles on both inhalation and exhalation, but you can also narrow the waist. Keep in mind that the internal and external obliques together with the transverse abdominis are the main muscles for holding in the abdominal viscera. These are the muscles that give you a narrower waist and help to force the air out of the lungs.
Thus, the key to developing the abdominals is to work each of the muscles in their main action. The rectus abdominis in flexion, the internal and external obliques in rotation (twisting) and the transverse abdominis with forced exhalation. By doing a minimum of four or more different exercises you will have full development of the abdominals. In addition, you will be able to achieve maximum definition of these muscles if your fat levels are also within an acceptable range.
For more information on execution of any of the above exercises read Biomechanics and Kinesiology of Exercise,
Note: This article was first published in Muscle and Fitness in the 1980s