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Biofeedback and Self-Regulation, Vol. 20, No. 1, 1995

Assessment of Lumbar EMG During Static and Dynamic Activity in Pain-Free Normals: Implications for Muscle Scanning Protocols I

Kenneth R. Lofland, Patricia B. Mumby, Jeffrey E. Cassisi 2 Illinois Institute of Technology

Nancy L. Palumbo Northwestem-Caremark Physical Therapy Center

Paul M. Camic Northwestem University Medical School

The purpose of this study was to provide a thorough description of lumbar surface integrated electromyography (EMG) in pain-free normals during a standardized assessment protocol of static isometric and unresisted dynamic tasks. It has been proposed that in pain-free normals, symmetrical tasks that bend the trunk forward or extend the trunk backward produce symmetrical paraspinal EMG activity, and asymmetrical tasks that rotate or laterally bend the trunk produce asymmetrical paraspinal EMG activity. In addition, it has been observed that lumbar EMG assessment during static tasks has been more consistent than tasks involving dynamic activities. Twenty-eight pain-free normals were assessed during symmetrical and asymmetrical tasks in both static and dynamic activities in a counterbalanced manner. The assessment of paraspinal EMG pattems was conducted while subjects were secured in a triaxial dynamometer, which provided standardization of body position and concurrent measurement of torque, range of motion, and veloci(y. The results provided experimental evidence for the above-stated propositions. An implication derived from this research is that clinicians may be better served utilizing local norms when using EMG for classification purposes.

1The authors would like to thank Allen Wolach, Ph.D. for his statistical consultation. 2Address all correspondence to Jeffrey E. Cassisi, Ph.D, Department of Psychology, Illinois Institute of Psychology, IIT Center, Chicago, Illinois 60616-3793.

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0363-3586/95/0300-0003507.50/0 © 1995 Plenum Pubtishing Corporation

4 Lofland, Mumby, Cassisi, Palumbo, and Camic

DESCRIPTOR KEY WORDS: Biofeedback; EMG muscle scanning; isometric; dynamic; lumbar assessment.

Nouwen and Bush (1984) and Dolce and Raczinski (1985) reviewed the relationship between surface paraspinal electromyography (EMG) and chronic low-back pain (CLBP). Both reviews independently concluded that the evidence relating EMG and CLBP came primarily from anecdotal case studies or methodologically flawed investigations. Previous assessment techniques orten used single-channel absolute EMG levels, which yielded equivocal results. Since these reviews, there have been many advances in EMG technology that have allowed for routine and detailed multichannel assessment of patterns of muscular activity.

Recent methodologically sound research has shown modern mul- t ichannel surface EMG to be reliable (Ahern, Follick, Council, & Laser-Wolston, 1986; Arena, Sherman, Bruno, & Young, 1990) and valid (Arena, Sherman, Bruno, & Young, 1991; Sherman, 1985). Furthermore, recent studies have repeatedly demonstrated the utility of EMG in identi- fying subgroups of CLBP patients and pain-free controls (Arena, Sherman, Bruno, & Young, 1989; Cassisi, Robinson, O'Connor, & MacMillan, 1993; Lofland, 1994).

Price, Clare, and Ewerhardt (1948) were the first to study patterns of EMG activity during movement and in relation to pain. They reported that areas of pain or tenderness in patients offen migrate. This shift in pain is associated with abnormal patterns of muscle activity developed in an attempt to avoid or relieve pain. Hyperactivity of a muscle was hypothe- sized to be due to reflex spasm or an attempt to avoid using another muscle whose activity produced pain. Therefore, EMG elevations could be expected either on the same side as a painful region or on the side contralateral to the pain. It was stated that hypoactivity results from reflex inhibition due to pain or the threat of pain.

The substantial literature on single-channel EMG amplitude in CLBP patients from the 1970s proved to be of little clinical utility (Dolce & Raczinski, 1985). However, general interest in EMG patterns and CLBP was revived by Wolf, Nacht, and Kelly (1982) in a discussion article published in Behavior Therapy. They described the aberrant patterns of paraspinal EMG activity based on their work with CLBP patients and pain-free controls. They indicated that the most simple pattern of EMG is comparing muscle tension levels on one side of the body with levels on the opposite side of the body. They found that during trunk rotation in a standing position, significantly greater EMG was detected in the paravertebräl muscle group (L3-L4-L5) contralateral to the direction of the movement.

Lumbar EMG 5

About that time, several empirical studies appeared supporting their perspective. Hoyt et al. (1981) found significantly greater absolute left-right differences in paraspinal EMG in CLBP patients than in pain-free controls during ten minutes of standing, but not in other positions. Cram and Steger (1983) also found that CLBP patients have larger left-right differences than pain-free controls in lumbar and cervical paraspinal EMG while standing, indicating a possible postural disturbance.

However, not all studies were so conclusive. While Collins, Cohen, Naliboff, and Schandler (1982) found marked absolute left-right differences in paraspinal EMG activity during exertive asymmetrical flexion tasks, they found no significant differences between CLBP patients and pain-free controls. In addition, Nouwen, Van Akkerveeken, and Versloot (1987) found no support for CLBP patients showing greater asymmetry than pain-free controls in left and right paraspinal EMG during symmetrical movements.

Nouwen et al. (1987) interpret the equivocal findings above by indicating that the two studies that found significant paraspinal EMG differences in CLBP patients versus pain-free controls did so while subjects were in a static posture (Cram & Steger, 1983; Hoyt et al., 1981), while the two studies that failed to find paraspinal EMG differences examined subjects during dynamic activity (Nouwen et al. 1987; Collins et al. 1982). Additional research is clearly needed to identify typical EMG patterns during static and dynamic activity. This is a prerequisite for the generation of norms for both the pain and nonpain populations during standardized EMG assessment protocols.

The following hypotheses derived from a clinical manual on the applicat ion and interpretat ion of EMG (Donaldson & Donaldson, 1990, pp. 148-151) were empirically tested in this study on pain-free normals: (1) EMG is symmetrical during isometric, symmetrical effort; (2) EMG is symmetrical during dynamic, symmetrical movement; (3) EMG is asymmetrical during isometric, asymmetrical effort; and (4) EMG is asymmetrical during dynamic, asymmetrical movement. It is imperative to empirically investigate these rules since they are currently being used in clinical practice.

Donaldson and Donaldson (1990, pp. 168-169) also propose that a 20% difference (PD) between left and right EMG in the paraspinal muscles should be considered an asymmetry. They state that this rule is speculative based on the retrospective examination of data from approximately 300 subjects in pain and 40 nonpain subjects. They found that 97.5% of the pain subjects had greater than a 20 PD, whereas most of the nonpain subjects had a 5-10 PD.


In addition, this study provided the opportunity to compare the relative performance of static versus dynamic EMG assessment within the same subjects. Isometric tasks have the advantage of decreasing movement arti- fact while obtaining accurate paraspinal EMG measurement during muscle activity. Based on the assertions of Nouwen et al. (1987), the specific hy- pothesis tested was that patterns of EMG responding will be more consistent during static isometric tasks than unresisted dynamic tasks.

Lastly, this study describes the paraspinal EMG patterns during isometric and unresisted dynamic tasks in the B200 Isostation TM, a triaxial dynamometer . The B200 provides standardization of body position and measurement of force production. No previous study of dynamic EMG has provided concurrent measurement and control of body position.

METHOD

Subjects

Twenty-eight subjects, 14 males and 14 females, aged 18 to 42, served as voluntary participants in this investigation. Subjects were recrui ted from a variety of sources (e.g., physical therapy center employees, undergraduate and graduate students, faculty members). All participants were examined by a licensed physical therapist specializing in spinal disorders and were de te rmined to be free from spinal dysfunction (e.g., pelvic obliquity, leg length discrepancies, and gross spondylolisthesis). Exclusion criteria included the presence of heart disease, back pain symptoms, or any medical condition which could be exacerbated by participation in the study.

Materials

The assessment of lumbar function was recorded by the B200 Isostation TM (see Fig. 1), from Isotechnologies, Inc. Hillsboro, NC (Parnianpour, Li, Nordin, & Kahanovitz, 1989; Parnianpour, Nordin, Kahanovitz, & Frankel, 1988). This device is a triaxial dynamometer which measures the angular position, angular velocity, and torque about three axes of motion: (1) flexion and extension (FLEX and EXT); (2) left and right lateral flexion (LLAT and RLAT); and (3) left and right rotation (LROT and RROT). It provides static measures of isometric flexion and extension strength, measures of maximum and average

Lumbar EMG 7

Fig. 1. The B200 Isostation; photograph provided by Isotechnologies, Inc.

torque and velocity, as weil as measures of range of motion (ROM) and total angular excursion. The B200 literature purports that this device can measure torque dynamically through a sophisticated system of counterbalancing, while producing minimal resistance. The subject stands on a platform which can be raised or lowered and the pelvis is restricted via two pads placed over the anterior superior iliac spines at about 45 degrees to the sagittal plane. Harness straps affix the upper trunk and other straps are placed around the anterior rib cage and at different locations on the legs. The instrument establishes the neutral position based on the subject's erect position before each trial.

The EMG signal was digitized with the Bioprompt TM Portable E M G computer and software by EMPI, Inc., St. Paul, MN. This appara tus incorporates au tomated gain adjus tment th roughout a dynamic range of .10 to 1800 microvolts root-mean-square (RMS) with


dynamic l inear sensitivity. The E M G signal was f i l te red with a bandwidth of 100-540 Hertz (Hz). This is a widely used bandwidth, which minimizes the noise in naturalistic settings but has been criticized for being limited in its ability to detect lower-frequency activity, which is thought to be associa ted with chronic pain condi t ions (Roy, DeLuca, & Casavant, 1989). An additional 60-Hz notch filter was a d d e d by the m a n u f a c t u r e r in o rde r to minimize any ro l l -o f t attenuation. The raw signal was processed through a RMS converter, which was sampled at 128 samples per second. The time constant for RMS to DC conversion was 25 milliseconds and the RMS to DC output rise was 40 milliseconds. Average integrated EMG was computed and stored for each repetition cycle described below. This resulted in 12 average values calculated from 5-second exertion periods. The 12 values are based on assessment in 3 planes of motion, times 2 directions within each plane, times 2 activities (static and dynamic).

Procedure

The rationale and procedure for the study were described and an informed, written consent was obtained from each subject. Subjects were then examined by the physical therapist to be evaluated for exclusion criteria. Prior to placement in the B200, subjects had 2 sets of three reusable silverized cloth electrodes (EMPI, Inc., St. Paul, MN) placed bilaterally with one active electrode at L1, the second at L4, and the ground in between. Each active recording surface was a 2.5-cm by 5-cm horizontal strip placed approximately 1.25 cm from the spiny process (Basmajian & Blumenstein, 1989). Fabric electrodes have been shown to have a .86 to .99 within-subject correlation with standard silver/silver chloride electrodes during isometric exercise (Chastain, Cassisi, Wilner, Knecht, & Keenum, 1992). The electrodes were affixed to an elastic waist belt with Velcro TM, connected to two EMG units, and attached to the portable IBM TM compatible computer. Placement was periodically inspected throughout the protocol to prevent shifting of electrodes.

The physical therapist then fastened the subjects into the B200 in order to isolate and stabilize trunk functioning in the standing position. In general, this apparatus greatly minimizes rotation and movement of the pelvis, thus isolating trunk movement. This is accomplished by means of an adjustable restraint system applied according to subject's individual bony

Lumbar EMG 9

landmarks, including pads at the sternum, Tl2 vertebral level, sacrum, anterior superior iliac spine of the pelvis, and straps at the greater trochanter and just above the patella.

Once subjects were secured, they were led through the B200 sequence of isometric and unresisted dynamic phases while having EMG recordings taken. Both phases included two sets of exertive tasks in the six directions described previously (left and right rotation, flexion-extension, and left and right lateral flexion). The isometric phase was accomplished with the B200 locking subjects in place in an upright, standing position. Subjects were instructed to exert maximally in the prescribed plane for five seconds (ca- denced by the B200 monitor and counted aloud by the physical therapist). The unresisted dynamic phase was accomplished with the B200 unlocked, allowing free movement with near-zero resistance. Subjects were instructed to move in the prescribed plane as far as possible in both directions at a slow and steady speed. The presentation of the isometric and dynamic phases was counterbalanced. The procedure took approximately 30 minutes, after which the subject was released from the B200 and informed of their results.

RESULTS

Because of the number of comparisons anticipated in the study, the level for statistical significance was set a priori at a conservative p < .01. Analyses were run on demographic variables and a significant gender difference was obtained on height, with males (M = 69.8 inches; SD = 2.2) being taller on average than females (M = 66.1 inches, SD = 3.2), t(26) = 3.42. There was no significant weight difference between males (M = 160 pounds, SD = 29.9) and females (M = 141 pounds, SD = 26.4). Also, there was no significant age difference between males (M = 24.5 years, SD = 7.0) and females (M = 27.5 years, SD = 6.6).

The significant height by gender effects in the present study, coupled with consistent findings of gender differences in previous research (e.g., Wolf, Basmajian, Russe, & Kutner, 1979), indicated that gender should be a variable in subsequent analyses.

The average EMG data from a 5-second standing baseline was calculated and appears in Table I. In addition, the isometric exercises are presented by direction and side in Table I. A 2 (gender) × 2 (side) × 6 (direction) analysis of variance (ANOVA) with repeated measures over the last two factors was conducted on the average EMG data from the

10 Lofland, Mumby, Cassisi, Palumbo, and Camie

Table I. Average EMG (RMS) by Direction of Exercise and Side of Monitoring

Left (SD) Right (SD)

Standing baseline 6 (4) 5 (3)

Isometric exercise FLEX 7 (6) 7 (6) EXT 36 (31) 35 (30) LLA'I ~ 24 (20) 9 (6) RLAq ~ 8 (36) 26 (18) LRO'I ~ 22 (24) 13 (15) RROq ~ 11 (9) 19 (10)

Dynamic exercise FLEX 9 (5) 8 (4) EXT 16 (10) 15 (11) LLAT 11 (6) 8 (6) RLAT a 9 (6) 13 (10) LROq ~ 17 (9) 11 (6) RROq ~ 11 (6) 15 (7)

Note: FLEX and EXT, flexion and extension, LLAT and RLAT, left and right lateral flexion; LROT and RROT, left and right rotation.

a Left and right significantly different at p < .01.

isometric exercises (Kirk, 1982, p. 535). No significant main effect for gender was obtained. However, a significant main effect for direction was obta ined , F(130,5) = 57.23. In addit ion, a significant interact ion for direction by side was obtained, F(130,5) = 43.51. Simple main effects tests (Kirk, 1982, p. 365) were performed for the significant side by direction interaction. These simple main effects tests compared the left and right sides in a given direction of isometric exercise. Neither of the simple main effects tests for side from the two symmetrical exercises FLEX or EXT were significantly different. The simple main effects tests for side from the asymmetrical exercises LLAT, F(1, 131) = 30.90, RLAT, F(1,131) = 41.47, LROT, F(1, 131) = 10.18, and RROT, F(1,131) = 8.62 were significantly different. The ipsilateral side to the direction of both rotation and lateral flexion was significantly higher than the contralateral side during all four of the asymmetrical isometric exercises.

The average E M G data from the dynamic exercises are also presented by direction and side in Table I. A 2 (gender) x 2 (side) x 6 (direction) A N O V A with repeated measures over the last two factors was conducted on the average E M G data from the dynamic exercises. No significant main

Lumbar EMG 11

effect for gender was observed. However, a significant main effect for direction was obtained, F(130,5) = 12.71. In addition, a significant interaction for direction by side was obtained, F(130,5) = 11.90. Simple main effects tests were performed for the significant side by direction interaction. These simple main effects tests compared the left and right sides in a given direction of dynamic exercise. Neither of the simple main effects tests for side from the two symmetrical exercises FLEX or EXT were significantly different. The simple main effects tests for side from R L A T , F(1,131) = 7.35, LROT, F(1,131) = 29.13, and R R O T , F(1,131) = 14.92 were significantly different. The ipsilateral side to the direction of both rotation and lateral flexion was significantly higher than the contralateral side during three of the four asymmetrical dynamic exercises.

The PD between left and right EMG was computed for each isometric task by subject using the following formula: [(higher v a l u e - lower value)/lower value] x 100 (Donaldson & Donaldson, 1990). The average PD from the standing baseline was also computed (M = 86, SD = 86). The average PDs are presented by direction in Table II. A 2 (gender) × 6 (direction) ANOVA with repeated measures over the last factor was conducted on the average PD data from the isometric exercises. No significant main effect for gender or significant interaction was obtained. However, a significant main effect for direction was

Table II. Average Percent Difference (PD) Between Left and Right EMG for Isometric and Dynamic Effort Across Syrnmetrical and Asymmetrical Exercises

Isometric a Dynamic

PD (SD) PD (SD)

Symmetrical exercise FLEX 81 (86) 81 (95) EXT 89 (134) 63 (73)

Asymmetrical exercise LLAT 271 (291) 140 (213) RLAT 250 (291) 122 (126) LROT 193 (173) 118 (129) RROT 135 (144) 78 (111)

Note: FLEX and EXT, flexion and extension; LLAT and RLAT, left and right lateral flexion; LROT and RROT, left and right rotation.

a Isometric FLEX is significantly different from isometric LLAT and RLAT, atp < .01. Isometric EXT is significantly different from isometric LLAT and RLAT, at p < .01.


obtained, F(130,5) = 6.36. Tukey's honestly significant difference test (Kirk, 1982) revealed that the PD from FLEX was significantly different from both LLAT, q(28) = 5.92, and RLAT, q(28) = 5.28. In addition, the PD from EXT was significantly different from both LLAT, q(28) = 5.63 and RLAT, q(28) = 4.99. Therefore, the two symmetrical exercises did not differ from each other in the PD between left and right EMG, but they each were significantly lower than the PDs produced during the two asymmetrical exercises involving lateral movement.

The process for computing PDs was repeated for the dynamic exercises. A 2 (gender) x 6 (direction) ANOVA with repeated measures over the last factor was conducted on these data. No significant main effect or interaction was obtained on the PDs from the dynamic exercises.

The isometric torque data are presented by gender and direction in Table III. A 2 (gender) x 6 (direction) ANOVA with repeated measures over the last factor was conducted on the average torque data from the isometric exercises. A significant main effect for gender was observed, F(26,1) = 17.28. In addition, a significant main effect for direction was obtained, F(130,5) = 87.54. Also a significant gender by direction interaction was obtained, F(130,5) = 6.85. Simple main effects tests were

Table III. Average Torque (foot pounds) by Gender and Direction of Exercise

Males ( SD ) Females ( SD )

Isometric exercise FLEX a 55 (30) 25 (12) EXT a 97 (36) 50 (16) LLAT ~ 67 (37) 32 (10) RLAT a 67 (28) 35 (14) LROT 36 (21) 16 (5) RROT 43 (20) 20 (7)

Dynamic exercise FLEX a 5.3 (.7) 6.0 (.7) EXT 4.5 (,7) 5.1 (.7) LLAT 2.9 (.5) 3.9 (.8) RLAT a 3.0 (.7) 4.0 (.9) LROT 2.8 (.5) 3.0 (.5) R R O T 2.8 (.4) 2.9 (.4)

Note: FLEX and EXT, flexion and extension; LLAT and RLAT, left and right lateral flexion; LROT and RROT, left and right rotation.

« Genders significantly different at p < .01.

Lumbar EMG

Table IV. Average Range of Motion (ROM) in Degrees and Velocity in Degrees Per Second During Dynamic Tasks

13

ROM (SD) Velocity (SD)

FLEX 46 (8) 29 (13) EXT 35 (4) 26 (12) LLAT 38 (6) 33 (14) RLAT 36 (6) 30 (13 LROT 36 (12) 28 (18) RROT 32 (7) 26 (15)

Note: FLEX and EXT, flexion and extension; LLAT and RLAT, left and right lateral flexion, LROT and RROT, left and right rotation.

performed for the significant gender by direction interaction. These simple main effects tests compared the males and females in a given direction of isometric exercise. The simple main effects tests for gender from FLEX, F(1,131) = 11.13, EXT, F(1,131) = 27.43, LLAT, F(1,131) = 15.04, and RLAT, F(1,131) = 13.19, were significantly different. Males produced more torque during these exercises. No differences were found by gender for LROT, or RROT.

The dynamic torque data are also presented by gender and direction in Table III. A 2 (gender) x 6 (direction) ANOVA with repeated measures over the last factor was conducted on the average torque data from the dynamic exercises. A significant main effect for gender was observed, F(26,1) = 10.72. In addition, a significant main effect for direction was obtained, F(130,5) = 197.3. Also, a significant gender by direction interact ion was obtained, F(130,5) = 6.02. Simple main effects tests were performed for the significant gender by direction interaction. These simple main effects tests compared the males and females in a given direction of isometric exercise. The simple main effects tests for gender from FLEX, F(1,131) = 7.37, LLAT, F(1,131) = 15.04, and RLAT, F(1,131) = 16.27, were significantly different. Females produced more torque during these exercises. No differences were found by gender for EXT, LROT, or RROT.

A 2 (gender) x 6 (direction) A N O V A with repea ted measures over the last factor was conducted on the average R O M during the dynamic tasks. No significant main effect for gender was observed. A significant main effect for direction was obtained, F(130,5) = 18.09. A 2 (gender) x 6 (direction) A N O V A with repeated measures over the last factor was conducted for the average velocity during the dynamic tasks. No significant main effect for gender was observed. A significant main effect for direction was obtained, F(130,5) = 8.89. The average


ROM and velocity by direction during the dynamic exercise are presented in Table IV.

DISCUSSION

The purpose of this study was to describe paraspinal EMG patterns in pain-free controls during comprehensive measurement of isometric and dynamic tasks. This is relevant to muscle scanning and EMG assessment protocols which are commonly applied in chronic pain rehabilitation.

Although the procedures in this study differ markedly from those of others, the results support the a priori hypotheses derived from Donaldson and Donaldson (1990). That is, asymmetrical tasks that rotate or laterally bend the trunk resulted in asymmetrical paraspinal EMG activity, while symmetrical tasks that bend the trunk forward or extend the trunk backward resulted in more symmetrical paraspinal EMG activity. Obtaining these congruent findings using a different protocol increases their reliability and makes them appear more robust.

Donaldson and Donaldson (1990) also suggested an objective criterion for the definition of symmetry in EMG assessment. Based on their clinical work, they suggested a 20 PD between left and right paraspinal muscles during maximum symmetric contraction to differentiate pain patients from pain-free controls. Applied to the differing procedures used in the present study, this criterion would be too stringent and would misclassify many pain-free controls as having pathological asymmetries. The average PD obtained in this study during the two symmetrical tasks was 85% during isometric effort and 72% during dynamic movement.

It is important to emphasize that while a 20 PD appears too low for the protocol described in this study, it may very weil be appropriate for other protocols. There were several important and obvious differences between this protocol and that of Donaldson and Donaldson (1990), which make absolute comparisons inappropriate. The fundamental conclusion to be drawn based on these findings is that the criteria for determining left-right PDs may vary based on the specific procedures implemented.

It should not be surprising that discrepancies were identified as there are many differences between the procedures used hefe versus those of Donaldson and Donaldson (1990) and other investigators. For example, the values obtained here during dynamic flexion were much lower than those obtained by others. Reasons for this may include that the integration period used here lasted 5 seconds and included EMG through the full range of motion. Donaldson and Donaldson (1990) assessed PDs at the point of

Lumbar EMG 15

maximum contraction. Another possibility is that the support and stabilization provided by the B200 resulted in lower paraspinal recruitment.

In accordance with Nouwen et al. (1987), isometric tasks were more reliable in producing the predicted asymmetries than were the dynamic tasks. Four out of the four asymmetrical, isometric tasks produced significant left-right EMG differences, whereas only three of the four asymmetrical, dynamic tasks produced the expected left-right EMG differences. Furthermore, the symmetrical and the asymmetrical PDs differed significantly during the isometric but not during the dynamic tasks. Thus, during the isometric tasks, the PD approach was meaningful in distinguishing between symmetrical and asymmetrical effort. However, during the dynamic tasks, the PD approach did not distinguish between symmetrical and asymmetrical tasks. Taken together, the results support the observation that static assessment protocols may produce more consistent results than dynamic assessment protocols.

The B200 provided concurrent measurement of torque output, ROM, and velocity. These parameters are free to vary in the dynamic assessment protocol used hefe. They have a significant impact on obtained EMG and they are provided to facilitate systematic replication and generalization of this type of research. However, it must be noted that the B200 has been criticized for poor stabilization (Dillard, Trafimow, Andersson, & Cronin, 1991). The primary factor contributing to this is the absence of complete pelvic fixation. Despite this potential weakness, measurements taken by the B200 were useful in many of the analyses. Compared to previous methodology, which relied on the experimenter to stabilize the pelvis manuälly, the B200 was an improvement.

One interesting area of inconsistency in this study versus previous studies relates to asymmetrical movements and the side that is most responsible for these movements. While it is agreed that one side is more involved during an asymmetrical movement than the other side, there are conflicting findings as to which side is most responsible. Wolf, Nacht, and Kelly (1982) found that during unresisted trunk rotation in a standing position, significantly greater EMG was detected in the paravertebral muscle group (L3-L4-LS) contralateral to the direction of the movement.

However, the present study found significant increases in activity in the muscle ipsilateral to the direction of the movement. This was found when monitoring over the L1-L4 paraspinals during asymmetrical tasks in both resisted isometric and unresisted dynamic tasks. Further support for increased ipsilateral EMG comes from McGill (1991). He monitored the EMG activity of the upper (T9) and lower (Iù3) erector spinae during left and right rotations. McGill (1991) argues that the relative activity within


a given muscle is associated with the direction of movement and is consistent with the fiber direction of an agonist muscle on one side, which produces twist, versus its antagonist counterpart on the other side of the body, which opposes the effort and has a lower activation level. He found large differences in activity between left and right sides during isometric exertions in the upper erector spinae, and smaller differences in the lower erector spinae. In both muscles, the right side was much higher when moving to the right (clockwise) and much lower when moving to the left (counter-clockwise).

Nouwen et al. (1987) monitored EMG at both the upper lumbar (L1-L2) paraspinals and the lower lumbar (L4-L5) paraspinals. They found higher contralateral than ipsilateral EMG during unresisted lateral bending in both the upper and the lower lumbar paraspinals. However, during lateral rotation, they found higher ipsilateral EMG in the upper lumbar paraspinals while still finding higher contralateral EMG in the lower lumbar paraspinals. Therefore, studies that have monitored specific areas (IA-L5) and measured lower lumbar paraspinal areas have found increased contralateral activity, and those studies that have monitored more global areas (L1-L4) and higher paraspinal areas have found ipsilateral increases. This distinction needs to be examined further.

In conclusion, these results support the principle of assessing patterns of EMG. However, the findings from this investigation are discrepant with Donaldson and Donaldson's 20 PD cutoff for symmetrical EMG. It is therefore recommended that concerned practitioners should avoid using one universal standard until important procedural permutations are explored. Rather, they should rely on local norms until protocols emerge that are standardized by the type of activity involved and equipment used. Future directions include replication of this protocol with pain patients as weil as examining how these EMG patterns relate to symptomatology. Further stratification by age as weil as gender should be undertaken in future research with larger samples. In addition, further investigations may explore and obtain normative data on the velcotiy of trunk movements and their effects on patterns of EMG activity in the lumbar paraspinals.

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assessment of lumbar emg during static and dynamic ......lumbar emg 5 about that time, several...

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