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Can Strong Abs Prevent Injury and Enhance Performance?


Rippled abdominal muscles get stares and double glances, but how important are they for torso stability to prevent low back pain and injury? And in the sports arena, can strong abdominals really enhance performance?

This article will explore valid and invalid techniques used to assess abdominal strength and discuss the interrelationship between abdominal strength, injury prevention and performance enhancement.

Definition

Unfortunately, the media and most individuals associate strong abs with appearance (six pack) rather than measured strength. In fact, few tests actually assess true abdominal strength. How is true strength of a muscle group defined? There is almost universal agreement that strength is force exerted one time or maximal output for one repetition. This is opposed to muscular endurance, which instead measures the number of repetitions one can perform for a given resistance.

Exploring Procedures

Perhaps the best known test to measure abdominal strength is the timed sit-up. Several organizations, including the National Youth Fitness Test, AAHPER, Boy Scouts (Fit for Tomorrow), West Point, Air Force Physical Fitness, Naval Aviation and Army and Marine Corps have used the timed sit-up as a gold standard in their fitness tests. Their standard protocol utilizes the number of sit-ups a person can perform while placing his/her hands either across the shoulders, behind the neck or alongside the body during a 30- or 60-second time period. Even though over 52 different variations of the sit-up technique have been reported, both physical educators and the military have used the straight leg timed sit-up as a measure of abdominal strength and endurance.

According to Soderberg, the straight leg sit-up contains three integrated parts:

  1. Upward pelvic tilt with reduction of the lumbar curve
  2. Spinal flexion, often referred to as the curl
  3. Flexion of the trunk and hip accomplished by movement of the pelvis on the femur

We now will explore some of the criticism levels at the various forms of sit-ups used to assess abdominal strength.

Sit-up Criticisms

The sit-up has been criticized by several authorities as being detrimental to the lumbar spine. They suggested that increased lordosis of the long lying sit-up can cause a forward displacement of the fifth lumbar vertebra on the sacrum while performing the sit-up motion. Moreover, the main muscles involved are the hip flexors. Perhaps the major criticism is that true abdominal muscle strength is not actually being measured as the number of sit-ups one can perform in a time period only assesses muscular endurance.

The sit-up motion can be performed either with the back flexed or arched. Performing a flexed back sit-up initiates two separate muscle actions. The first action brings the thorax to the pelvis. This flexed trunk then is raised on the legs by the hip flexor muscles to complete the sit-up. Flint and Lancey have found using EMG analysis that the abdominal muscles were primarily active only during the first phase of this sit-up. When the back is arched, there is only one phase during which the person doing the sit-up would be hyperextending his/her back as they lift off the surface. Soderberg has shown that the iliopsoas muscle is primarily active in the flat back sit-up, while others have shown an arched back can result in increased risk of low back injuries.

Flint measured the electrical activity during 12 different exercises using needle electrodes inserted into the upper and lower portion of the rectus abdominis (RA) and iliacus. He found the iliacus muscle (a strong hip flexor) was responsible for most of the muscle activity when the feet were held. Also intriguing is that when an individual goes beyond 45 degrees to a vertical position and then back again to 45 degrees, it was the iliacus muscle that was again most active. Others have found that the rectus femoris muscle and other major hip flexors were most active during the straight leg sit-up when the feet were held.

Besides the involvement of the hip flexors, Ricci found the lumbar spine extended rather than flexed at the beginning of a typical sit-up. This raised contradictions by other authors who claimed that their subjects never hyperextended during sit-ups. Ricci also found that the type of muscle contraction in the RA and external obliques initially is eccentric, followed by concentric and finally isometric contraction. On author claimed that dynamic sit-ups do not challenge the abdominal muscles to change length; rather, they remain isometrically contracted throughout the range of motion.

In summary, the straight leg sit-up may aggravate the lumbar lordotic curve, involves primarily the hip flexors and testing the number of sit-up repetitions an individual can perform does not measure abdominal strength.

Disadvantages of Presently Prescribed Sit-ups

Due to hip flexor involvement and hyperextension (which produces stress in the lower back), the straight leg sit-up was changed to a bent knee approach. Theoretically the bent knee sit-up reduces the lordotic curve by causing the iliopsoas to shorten and relax. Unfortunately, theory and practice are not compatible in this case. Bending the knees may flatten the back to allow for a posterior pelvic tilt, but a complete range of motion in the sit-up still requires the hip flexors to contract with significant force. In addition, bending the knees will shorten the lever, making it more difficult to keep the feet on the floor. As a result, the tests that were developed using bent knees also required the feet to be supported, thereby increasing hip flexor activity and reducing involvement of the abdominal musculature. Furthermore, if one arches the back, rather than maintaining a completely curled position (which would truly require more involvement of the RA), then hyperextension of the lumbar vertebrae would occur using the iliopsoas as the main muscle. Some have even claimed that the straight leg sit-up is safer than the bent knee version due to the center of gravity being closer to the ischium. Because of these problems, several attempts were made at developing a “curl up,” limiting range of motion to no more than 30–45 degrees. This was shown to increase activation of the abdominal muscles and reduce activity of the hip flexors. Robertson and Magnusdottir introduced the first crunch or partial sit-up. Although similar to the bent knee sit-up, it had distinct differences. First, arms were placed at the sides of the torso (hands flat on floor), and the subject’s hands were slid forward until the fingertips touched a specific frame on the floor. If done correctly, only the head, shoulders and upper torso were lifted off the ground. This abdominal curl-up has replaced sit-ups mainly due to the reduced stress to the lower back and less involvement of the hip flexors along with greater involvement of the abdominals. Even with these significant changes in procedure to make sit-ups a more valid tool, Hall found little relationship (low correlations) between sit-ups, curls and abdominal strength using isokinetic tests to evaluate abdominal strength. Of course, the practicality of using expensive and time consuming isokinetic tests limits its usefulness as a tool to evaluate abdominal strength in the field. As long ago as 1946, Wedemeyer, using an ingenious test to measure the “breaking force” that abdominals could withstand before collapsing, found no relationship between the number of sit-ups performed and abdominal strength.

The ABMED System

Our research team at the University of Arkansas embarked on a series of studies over a period of three years to develop and validate a technique to measure abdominal strength. We have discarded several iterations that held promise but failed the important criteria of precision, accuracy, reliability or validity. Finally, after many attempts and extensive testing in industry, athletics and school settings, we settled upon a technique that shows a great deal of promise and truly measures strength. The system we developed called ABMED (ABdominal Measuring Device) had to meet the following criteria:

  1. The system must fulfill the criteria of strength – it must measure 1RM, not how many repetitions can be performed in a specified time period (endurance).
  2. Based upon previous research, the point at which strength is measured could not exceed 45 degrees. Beyond this angle, hip flexion predominates and spinal flexion (using the RA) is limited.
  3. It must avoid any type of ballistic movement that might cause hyperextension of the lumbar area.
  4. The force applied must be reflective of abdominal flexion.
  5. Ankles or feet could not be held, thereby avoiding use of the hip flexors during the test.
  6. The test had to be repeatable within five percent error.
  7. Using either face validity and/or EMG corroboration, known principles of strength assessment for other muscles groups had to be followed to validate the procedure.

We have fulfilled the first six and portions of the seventh criteria and have completed correlational studies looking at the relationship between ABMED, back strength, body fat, lumbar flexibility, nutritional status, health risk and low back pain. Although the data is still being analyzed, we’ll describe, show some photos and present some of our initial findings. If this procedure becomes the norm for assessing abdominal strength, we expect many others will begin serious and meaningful investigations into performance, health status, injury and abdominal strength. The ADMED procedure is described below with accompanying photos.

How Does ABMED Work?

The new procedure utilizes a device consisting of a strain gauge attached to a cushioned arm and placed across the xyphoid process (see Figure 1).

Figure 1. Resting position with cushions placed on xyphoid process.

This test records the force (lbs) exerted by the abdominal musculature without ankles being held as the subject positions herself at a 30 degree angle horizontally. A back rest at this angle ensures uniformity. The posterior aspect of the ankle at the level of the calcaneous ankle bone is placed on a support platform so that the angle at the knee and hip is 90 degrees. Arms are folded across the chest with opposite arms held securely at the acromion process of opposite shoulders. The subjects were instructed to exert a gradually increasing force against a cushioned arm (see Figure 2) until a maximum effort was attained within a three to five second period.

Figure 2. Subject exerts force on transducer. Notice knees are at right angle and feet are not held. Figure 3. Force displayed (lbs) as subject presses against transducer.

An Omega electronic digital display records the force output and stores the maximum effort achieved. The maximum force is recorded and later used for data analysis. To date, we have tested over 500 subjects. Each person was re-tested after a 10 second rest to evaluate reliability (repeatability). It’s important to note that we experimented with several different angles from 15 degress to 60 degrees and also placed the feet and arms in several different positions. Also, the transducer was positioned across different areas of the chest and abdomen. The highest repeatability, ease of testing and ability to discern differing levels of strength was obtained using an angle of 30 degrees with arms folded across the chest, transducer placed at the xyphoid process, knees flexed at 90 degrees and plantar surface of feet placed on top of the support.

Scientific Research

In studies we conducted, each subject was asked to perform a timed sit-up with hands folded behind the neck, knees at a right angle and feet held by another subject. In addition, we measured back strength, lumbar flexibility and body fat then asked each person to fill out a questionnaire regarding the incidence and severity of low back pain. We conducted these tests on different groups of individuals from high level athletes (male and female) to blue collar workers at a chicken plant to skilled laborers and secretaries at an electronics firm.

Findings

The ABMED high reliability (r=.93). A small and non-significant correlation (r=.26) was found between the number of sit-ups performed and abdominal strength measured with the ABMED for all groups combined. Although body weight appeared to be moderately related to abdominal strength using the ABMED (r=.65), there was no relationship to the number of sit-ups performed (r=.14). Between 14 and 65 sit-ups were performed in one minute, and abdominal force ranged from 14 to 82 pounds (6.4 to 37.3 kg). We have established norms (which we expect to refine as more categories in the workplace, school and on the athletic field are evaluated) that are shown in Table 1. So far, we’ve tested over 500 individuals, but only 164 have completed the entire battery of tests described in Tables 1 through 4. With this limited number of subjects, we have decided to present the data categorized only by age. As a larger database is accumulated, we will further subdivide the norms by age. It’s also interesting to observe the back strength (Table 2), lumbar flexibility (Table 3) and body fat levels (Table 4) of these groups. The blue-collar workers represent three different corporate settings that may reflect the general state of fitness (or unfitness) of workers in industry today. There was a slight tendency for those who possessed less body fat to have stronger abs and a stronger back. Presently, we have not found any dramatic relationship between abdominal strength and the incidence of low back pain. This is probably due to the fear of participants who are working for large companies admitting to low back pain for fear of losing their jobs. As we continue to conduct research with ABMED, we will reconstruct the questionnaire and probably resort to individual interviews to clarify the questionnaires and reduce the fear the workers have of job loss.

Percentile (%)

Males (lbs)

Females (lbs)

10

33

14

25

38

17

50

48

24

75

56

34

90

68

68

Range

18-109

7-78

Table 1: Abdominal Strength (lbs) of Males and Females

Percentile (%)

Males (lbs)

Females (lbs)

10

111

42

25

127

60

50

146

74

75

170

90

90

181

104

Range

89-216

35-141

Table 2. Back Strength (lbs) of Males and Females

Percentile (%)

Males (degrees)

Females (degrees)

10

19

14

25

24

19

50

29

29

75

33

40

90

36

47

Range

10-54

5-69

Table 3. Lumbar Flexibility (degrees of flexion) of Males and Females

Percentile (%)

Males (% body fat)

Females (% body fat)

10

14.8

27.8

25

22.1

30.7

50

27.3

37.2

75

32.6

40

90

36

42.1

Range

8.2-39.6

23.4-48.6

Table 4. Percent Body Fat of Males and Females

Significance of Strong Abs

A strong abdominal musculature may be an important factor to enhance athletic performance and prevent back injury. It has been assumed that abdominals need to be sufficiently strong to withstand shear and rotational forces during various life and sport-related activities. Often the coach, trainer or biomechanist will refer to the midsection as a stabilizing base that allows either the upper or lower torso to generate extreme forces during lifting or propulsive activities. It is during extreme rotational and force requiring activities that low back injury and pain results. In normal life activities and at work, low back injury is also of great concern. In fact, NIOSH (National Institute of Occupational Safety and Health) has been interested for years in quantifying the strength of trunk musculature to evaluate the effects of abdominal and trunk strength upon the incidence of low back injury. Not only do abdominals play a major role in preventing low back pain, there is extensive economic and productivity loss associated with low back injury. Indeed, the backache is second in incidence of complaints in doctors' offices to the common cold and has been called “the albatross of industry” with over 60% of all Americans most likely to see an MD about a backache sometime during their lifetime.

Several authors have looked at the relationship between strength and low back pain. Often, the assessment of strength has been instituted in industrial and athletic settings to help in identifying people at risk for low back pain. Now, our job (i.e., all of us) must focus on identifying and using the most effective techniques for evaluating strength if we are to reverse the economic loss and human pain suffered by millions of people worldwide.

Can Strong Abs Enhance Performance?

The role of the abdominal musculature in performance is two-fold: 1) abs act as a stabilizing force along with the back extensor muscles for the spinal column and provide an essential base of support for the upper and lower extremity during extreme power movements of either extremity; and 2) abs allow a more forceful forward propulsion of the hamstring muscles during running.

The stabilizing function of abs does not contribute directly to enhance performance but prevents injury and allows a fulcrum around which the upper or lower extremity can exert massive force. Activities where strong abs play a particularly important role in this regard include wrestling, American football, field events (e.g., hammer throw, shot put, etc.), and gymnastics (and most activities where a pike is required or desirable).

In running activities, strong abs allow a forceful propulsion in the following manner:

  1. The rectus abdominis pulls on the superior ramus of the pubic bone to draw the pelvis superiorly and posteriorly.
  2. This posterior tilt causes the hip flexors (e.g., rectus femoris, sartorius, etc.) to stretch, thereby allowing high knee action (or hip flexion) to occur with greater force and consistency.
  3. High knee action (or hip flexion) allows for longer stride length.
  4. Longer stride length stretches the hamstring muscle.
  5. As the foot makes contact with the ground, the stretched hamstring provides greater propulsive force (retrograde motion) to pull the runner forward.

The next time you watch a 1500 meter or mile run, look at the forward tilt of a runner during the last 400 meters. The runner who assumes a more upright posture is trying to compensate for weaker abdominals to stretch his/her hip flexors. This is a biomechanically unsound running posture and reduces the force applied in the forward vector (i.e., reduced speed in a forward direction). The runner who assumes a greater forward lean has stronger abs and allows more of his force to be used in a horizontal plane and will most likely win the race. Of course, there are always exceptions to this rule. One need only look at Michael Johnson’s upright running style and compare his win-loss record to other sprinters. Yet, he is not a distance runner where abdominals may play a greater role as hip and knee flexors begin to tire.

Abs are extremely important to prevent injury and serve as stabilizers of the upper and lower extremity during explosive power movements. They are also intimately involved in increasing stride length and stretching hamstrings to promote greater force production during running. We are only beginning to understand the role that abdominals play in all types of athletic performance.

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