April 2006

Strengthening the Core

By Eric G. Johnson, PT, DPTSc, and Jerrold Petrofsky, PhD

The effects of core muscle conditioning benefits those with disabilities.

Figure 1: A patient strengthens her core muscles with a timed 6-second lower abdomen obliques exerciser.

Studies show that core muscle strengthening contributes to increased functional abilities in persons with disabilities.^12-13 An important component of rehabilitation is the development of exercise techniques that allow individuals who are disabled to exercise at home.¹⁴ One such device is a timed 6-second lower abdomen obliques exerciser. This abs machine provides a progressive increase in resistance using rubber tubing with a built-in, 6-second exercise pace timer and enables individuals with disabilities to exercise their abdominal and lower back muscles from a wheelchair (see figure 1).¹⁵ The purpose of this study was to determine the effects of the abs machine on functional reach, balance, and core strength in individuals with disabilities.

Fourteen subjects with neurological conditions including paraplegia, multiple sclerosis, and stroke participated in the study. Thirteen age-matched control subjects free of any physical disabilities also participated as a basis of comparison (see Table 1 below). Controls sat in wheelchairs in order to directly compare them to people with disabilities.

Strength was measured in the abdominal and back muscles using a strain gauge force sensor that was placed around the subject's chest just below the axilla. Balance and multiplanar functional reach were assessed using a computerized dynamic posturography device that was built to accommodate wheelchair-bound subjects and a modified functional reach test (FRT), respectively (see figure 2).¹⁶ With the wheelchair placed on the center of the platform, leaning in any direction was then transduced through strain gauges so that the deviation and center of gravity could be assessed.

Figure 2: A computerized dynamic posturography assesses a patient’s balance and reach.

Subjects exercised a total of 20 minutes 3 days per week for 4 weeks. The four different exercises using the 6-second lower abdomen obliques exerciser were performed as follows: (Exercise 1) subjects sat in the wheelchair facing forward to exercise the rectus abdominis muscles; (Exercises 2 and 3) subjects sat facing 45º to the left and 45º to the right to exercise the external and internal oblique muscles; (Exercise 4) beginning in 30º of seated trunk flexion, the abdominal exerciser was placed under the subject's arm and they extended their back against the load of the exercise device. Each of the four exercises was performed for 5 minutes, and the repetitions consisted of a 3-second concentric contraction followed by a 3-second eccentric contraction. Electromyogram studies were performed for each exercise to confirm appropriate muscle activity.

Overall exercise compliance was 97.8+/-5.4%. Compliance was calculated by dividing the actual number of days subjects exercised by the total number of days they were asked to exercise. Post-test data revealed that significant increases were made in abdominal and back muscle strength (P < 0.01) (see Chart 2 below). Associated with this increase in muscle strength was a corresponding statistically significant (P< 0.01) increase in the FRT. (See Chart 3 results of the FRT before and after the 1-month training program in the sagittal and frontal planes below). These increases in reach were all statistically significant (P< 0.01) when comparing pre- and post-reach data. There was no difference in the gain in strength or reach in any of the three subgroups of neurologically impaired subjects examined (P>0.05). Associated with the increase in functional reach was an increase in the ability of subjects to shift their center of gravity (COG) without losing balance. These shifts in the COG were statistically greater than seen in the same subjects before the 1 month of exercise (P< 0.01).

While there are many benefits of daily exercise including strength, endurance, and increasing overall aerobic capacity, there may be the added advantage of strengthening core muscles for people with disabilities. ^1-3,17,18 The core muscles (erector spinae, transversus abdominis, and rectus abdominis muscles) stabilize the trunk and provide stability during dynamic functional activities such as reaching. Increased reach (movement of the COG away from the base of support) translates into more functional independence.¹⁰ There was significant improvement after 30 days of exercise in the ability to reach in the forward and side-to-side directions. A recent paper stated that the limits of stability (LOS) test in some cases does not correlate well with the FRT.¹⁹ In this study, with people in wheelchairs, there was a good correlation. This may be due to the fact that sitting in a wheelchair limits the strategies that can be used during reach. Reaching in standing is much more variable because movement can be achieved using the hips, knees, ankles, and/or shoulders.

In conclusion, for individuals with disabilities, strength, balance, and reach improved after strengthening the core muscles using the timed 6-second lower abdomen obliques exerciser for 4 weeks. The subjects were seen in the research laboratory for their initial instruction in the exercises and then performed the exercises independently as a home exercise program. The improvements translated into functionally important movements that improved the independence of the participants. (Portions of this paper were published in The Journal of Applied Research, Volume 5, Number 2, 2005.)

Table 1

Chart 2

Chart 3

Eric G. Johnson, PT, DPTSc, is an associate professor at Loma Linda University School of Allied Health Professions, Department of Physical Therapy; Jerrold Petrofsky, PhD, is a professor and Janaki Iyer, PT, is a graduate assistant at Loma Linda University, Loma Linda, Calif.

References

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15. Petrofsky JS, Morris A, Bonacci J, Bonilla T, Jorritsma R. Aerobic training on a portable abdominal machine. J Appl Res. In press.
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