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The purpose of this study was to analyze the results of a training method to increase voluntary recruitment of internal oblique and transversus abdominis.
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and JOHN M. MEDEIROS
The purpose of this study was to analyze the results of a training method to increase voluntary recruitment of internal oblique and transversus abdominis muscles. Forty volunteers were assigned to either a Control or an Experimental Group. Training consisted of multisensory (auditory, tactile, visual, and kines- thetic) cuing focused on the lower abdominal muscles during the slow curl-back (eccentric) phase of curl-up exercises with the subjects' feet unsupported. We recorded integrated electromyographic (IEMG) values using surface electrodes from internal oblique and transversus abdominis muscles during pretest and posttest exercises. Using an analysis of covariance, posttest IEMG values of the Experimental Group were significantly higher (p < .001) than the Control Group. Our results reveal that multisensory cuing with the feet unsupported during the curl-back is an effective method of increasing combined recruitment of internal oblique and transversus abdominis muscles. Motor skills developed by this technique are discussed in relation to optimal trunk function and rehabilitation.
Key Words: Abdominal wall, Exercise therapy, Physical therapy.
Common adult disorders of the trunk, such as low back pain and inguinal hernias, are associated with weakened lower abdominal muscles and their improper or inadequate use in daily activities.1-7^ In sedentary individuals, trunk muscle im- balance develops that favors strength in postural muscles, such as the iliopsoas, compared with weakness of the more phasically acting abdominal muscles.^7 In addition, the ilio- psoas muscle, with its extensive lumbar attachment, contrib- utes potentially hazardous compressive and lordotic forces on the lumbar spine^8 and intervertebral disks,^9 if not balanced by the stabilization forces of the abdominal muscles.3,7, Awareness and recruitment of abdominal muscles in exer- cise and daily activity appear to be required to maintain balance of the trunk musculature. Thus, training should be directed toward voluntary recruitment of abdominal muscles during common trunk training exercises such as the curl-up. Using electromyography, Janda and Schmid showed that stabilizing the feet dorsally during curl-ups facilitates iliopsoas muscle predominance.^7 Controlling the curl-up without the feet anchored requires pelvic stabilization and trunk coordi- nation skills, which are essential for functional trunk train- ing.3, In a pilot study, we used intramuscular EMGs recorded from fine-wire electrodes to examine the relationship of the iliopsoas, abdominal, and gluteus maximus muscles during
curl-ups, with and without dorsal foot stabilization. Our raw EMG data recorded from three subjects support the results of Janda and Schmid^7 and suggest that an inverse relationship exists between internal oblique and iliopsoas muscle activity during the curl-back (eccentric) phase of curl-ups. No other abdominal muscles appeared to be so closely related to ilio- psoas muscle activity during curl-ups. After training, the individuals' iliopsoas muscle activity decreased, whereas the activity of the abdominal muscles, particularly the internal oblique muscle, increased markedly. This apparent substitution would be anticipated from the anatomical and kinesiological similarities of the two muscles (Fig. 1). Both the internal oblique and the iliopsoas muscles are attached dorsally and ventrally and apply forces onto the pelvis and the spine (the iliopsoas muscle directly and the internal oblique muscle through its attachment to the lum- bodorsal fascia). The internal oblique and transversus abdom- inis muscles are the only two abdominal muscles that are attached from the anterior trunk to the lumbar spine by the lumbodorsal fascia, the strongest low back supportive struc- ture.3,11^ They also are the only abdominal muscles passing superior to the inguinal canal that supply active support in response to intra-abdominal pressure.^6 Authors of previous studies of abdominal muscle exercise have examined different muscle groups with different meth- ods. They have focused on the activity of the prime movers, specifically the rectus abdominis and external oblique mus- cles, rather than the stabilizing muscles that encircle the trunk—the internal oblique and the transversus abdominis muscles.12-18^ Previous studies have not incorporated motor learning techniques for facilitating trunk and hip flexor mus- cle coordination.12- The objective of this study was to examine a method that has been used clinically to teach individuals to end their
Ms. Miller is in private practice in low back education and rehabilitation in Neskowin, OR, and San Francisco, CA. She was a graduate student, Physical Education Department, San Francisco State University, when this study was completed in partial fulfillment of her Master of Arts degree. Address corre- spondence to 112 Montcalm St, San Francisco, CA 94110 (USA). Dr. Medeiros is Director, Motion Analysis Laboratory, Children's Hospital at Stanford, 520 Willow Rd, Palo Alto, CA 94304. This article was submitted November 12, 1985; was with the authors for revision 18 weeks; and was accepted September 25, 1986. Potential Conflict of Interest: 4.
Volume 67 / Number 8, August 1987 1213
Fig. 1. Anatomical attachments of the internal oblique, transversus abdominis, and iliopsoas muscles.
dependence on feet stabilization during curl-ups and to de- velop pelvic stabilization skills useful in daily activities of back care.^20 We analyzed the results of training designed to increase voluntary recruitment of the anterior fibers of the internal oblique and transversus abdominis muscles during the curl-back phase of curl-up exercises. Surface EMGs were processed by the technique of integrated electromyography (IEMG). Our training method consisted of multisensory cuing during the curl-back phase. We made comparisons between an Experimental Group and a Control Group. We hypothe- sized that no significant difference would occur in combined IEMG values from the anterior inferior portion of the internal oblique and transversus abdominis muscles when comparing the Control Group with the Experimental Group after train- ing.
METHOD
The subjects were healthy male volunteers, between the ages of 25 and 40 years, who were able to perform the test exercise without complications. The mean age of the total group was 31.1 years, the mean height was 181.1 cm, and the mean weight was 75.6 kg (Tab. 1). Before recruitment of the participants, we numbered files individually from 1 to 40. We then used a table of random numbers to classify each file as experimental subject (T) or control (C). We assigned a file to each subject corresponding to the chronological order in which he entered the study. Twenty subjects were in each group.
Instrumentation
Our instrumentation has been reported in detail else- where.21,22^ The EMG equipment used was designed to provide a frequency response of 10 to 200 Hz. The EMG unit con- sisted of a differential voltage amplifier driving a voltage control oscillator whose pulse frequency output was counted on an electronic counter. By counting the pulses, a direct integral of EMG voltage over time was obtained. When the integral was divided by the time base, the mean level of electrical activity in the muscle group over a period of time was recorded as microvolts root mean square (μVRMS). At all test sessions, the EMG signals were monitored continu- ously by the primary investigator (M.I.M.) using an oscillo- scope for identifying possible movement artifacts.
Procedure
On arrival, each subject read and signed a consent form explaining the procedure and purpose of the study. He then removed his shirt, belt, and shoes. His stockings remained on to decrease foot friction on the vinyl-surfaced plinth. A towel was used on the plinth where skin contact would be made. Each subject assumed a supine position on the plinth. The recording equipment was not visible to the subject. The primary investigator placed a ground electrode on the volar aspect of the subject's wrist and two active electrodes 15 mm apart and parallel to the inguinal ligament over the retroapo- neurotic triangle.1,23^ This site for IEMG recording of the internal oblique muscle is, as described by Floyd and Silver,
1214 PHYSICAL THERAPY
TABLE 2 Intraclass Correlation Coefficients
Variable
Pretest Posttest
Total Group (N = 40) . .
Experimental Group (n = 20) . .
Control Group (n = 20) . .
TABLE 3 Means and Standard Deviations of Integrated Electromyographic Pretest and Posttest Values and Adjusted Posttest Values (in μVRMS)
Variable
Pretest
s Posttest
s Adjusted post- test
s
Total Group (N = 40)
Experimental Group (n = 20)
...
Control Group (n = 20)
...
TABLE 4 Analysis of Covariance Comparing Control and Experimental Groups Source Covariates Pretest mean values Main effects Experimental Group Error TOTAL
df
1
1 37 39
SS
MS
F
P
.
.
adjusted based on the analysis of the pretest data to account for regression of pretest values. We used .05 as the level of significance. To determine reliability of the IEMG data, we analyzed the five individual test values for each pretest and posttest session using the alpha model intraclass correlation coefficient (ICC[l,k]).
The mean and standard deviation values for age, height, and weight of the subjects are shown in Table 1. The results of the ICC indicated that the pretest and posttest IEMG values were highly reliable (Tab. 2). Integrated electromyographic values are displayed in Table 3 and illustrated in Figure 3. As shown in Table 3, the mean adjusted pretest IEMG values were 72.37 μVRMS for the Experimental Group and 75. μVRMS for the Control Group. The mean adjusted posttest IEMG values were 144.60 μVRMS for the Experimental Group and 67.38 μVRMS for the Control Group. The ANCOVA revealed a statistically significant difference ( p < .001) between the Experimental and Control Groups (Tab. 4).
PRETEST POSTTEST
Fig. 3. Integrated electromyographic (IEMG) pretest and post- test values.
This study analyzes a training method to increase voluntary recruitment of lower abdominal muscles through the combi- nation of multisensory cuing with eccentric training.^25 As revealed by the ANCOVA, mean posttest IEMG values for the Experimental and Control Groups differed significantly from each other (Tab. 4). Kendall et al stated that most adults, especially adult men, must have their feet stabilized to perform a complete curl- up.^3 Janda and Schmid, however, found that stabilizing the feet dorsally reinforces the pattern of combined concentric action of the iliopsoas and abdominal muscles, with iliopsoas muscle predominance.^7 Based on our findings and those of Janda and Schmid, we believe that dorsal stabilization of the feet should be avoided during curl-up exercises. Stabilization by resistance applied to plantar flexion instead of dorsiflexion has demonstrated an inhibitory influence on the iliopsoas muscle^7 and, therefore, is a reasonable alternative if stabili- zation is required initially. Several sensory factors may influence the ability to perform curl-ups without requiring feet stabilization. The individual must develop physical awareness of the subtle substitution relationship of the abdominal muscles and the iliopsoas mus- cles to break patterns of dependency on the strength and dominance of the iliopsoas muscles. To experience this aware- ness, the individual first must challenge the substitution rela- tionship between the lower abdominal muscles and the ilio- psoas muscles by using a movement that involves the activity of both muscle groups. The individual then must learn to gain control with the lower abdominal muscles dominating the force of the movement. The means of such kinesiological awareness is through multisensory input. Various sensory neuromuscular tech- niques can be used for such training.26,27^ The cuing technique used in this study can be applied to large groups, without sophisticated training or equipment. The visualization cues to "contemplate your navel" and to "pull it up and against your spine with your abdominal muscles" use a familiar visual locus in the lower abdominal area from which the individual can focus the direction of motor response. The phrase "con- template your navel" not only provides a visual cue, but has
a humorous quality. If laughter occurs, the internal oblique and transversus abdominis muscles are further recruited be- cause they are major participants in the activity of laughter.1, The compressive and lordotic forces of the iliopsoas muscles on the spine and intervertebral disks are hazardous if allowed to predominate movement habits.^9 Because predominance of the iliopsoas muscles over the abdominal muscles during curl- ups is fostered when the feet are stabilized dorsally, the curl- up should be performed without such stabilization.^7 Unfor- tunately, curl-up exercises with the feet stabilized dorsally is the standard testing method used in school, military, and adult fitness programs in the United States.^28 The method discussed in this article teaches abdominal muscle awareness and voluntary control to break the patterns of dependence on the iliopsoas muscles in exercise and func- tional trunk movement. The specific trunk stabilization skills involved in this method are useful in other trunk movement methods including isolated posterior pelvic tilt and Kennedy's dynamic abdominal bracing,^10 techniques that require pelvic coordination independent of leg position, stabilization, or motion. The positions selected for this training method can be modified clinically for the individual, but the concept of increased awareness and control with the eccentric contrac- tion and multisensory input can be applied to any exercise variation selected. This method can be used in health educa- tion to encourage habits of trunk coordination and muscular balance that may be applied functionally and throughout the individual's life. Further examination of this training method should focus on the relationship of iliopsoas muscle activity to that of the
internal oblique muscle. Any study of the iliopsoas muscle requires intramuscular EMG, necessitating deep placement of needle electrodes. This training technique, which recruits muscular stabilization of the spine through attachments to the lumbodorsal fascia, should be applied to disk-compression studies of curl-up exercises.
We analyzed a training method designed to increase vol- untary recruitment of the internal oblique and transversus abdominis muscles during curl-up exercises. When comparing the Control Group with the Experimental Group, we found a statistically significant difference favoring the Experimental Group. The training method involved a slow eccentric, or curl-back, phase without foot stabilization and multisensory kinesthetic cuing for recruitment of the lower abdominal muscles. Factors suggested as having a possible influence on the positive results of the training method included the teach- ing of sensory awareness with multisensory cuing. This method demonstrates clinical potential for breaking the pat- terns of dependency on the iliopsoas muscle while developing the strength and functional coordination skills of the spinal and pelvic stabilizing muscles.
Acknowledgments. We express our gratitude to Steven Evans, PhD, and Frank Verducci, PhD, for their advice on research design and evaluation, and our thanks to Valerie Thorn for her valuable consultative services.
REFERENCES
1. Floyd WF, Silver PHS: Electromyographic study of patterns of activity of **the anterior abdominal wall muscles in man. J Anat 84:132-145, 1950
Volume 67 / Number 8, August 1987 1217