Trunk Muscle Activation Patterns and Spine Kinematics When Using an Oscillating Blade: Influence of Different Postures and Blade Orientations

Article Outline

• Abstract
• Methods
  • Subjects
  • Tasks and Data Collection
  • Data Analysis
• Results
• Discussion
  • Study Limitations
• Conclusions
• References
• Copyright

Abstract 

Sánchez-Zuriaga D, Vera-Garcia FJ, Moreside JM, McGill SM. Trunk muscle activation patterns and spine kinematics when using an oscillating blade: influence of different postures and blade orientations.

Objective

To compare trunk muscle activation patterns and trunk kinematics when using an oscillating blade in standing and unsupported sitting postures, and with different orientations of the blade.

Design

A cross-sectional survey of trunk muscle activities and lumbar motion.

Setting

Biomechanics research laboratory.

Participants

Healthy men (N=13).

Interventions

An oscillating blade was held with 2 hands and oscillated with vertical and horizontal orientations of blade. These exercises were performed both in an erect standing position and in an erect sitting position.

Main Outcome Measures

Surface electromyography from 14 trunk and 2 shoulder muscles, together with lumbar angular displacement in the 3 planes of motion, were measured while subjects used an oscillating blade at different performance variations. Electromyographic signals were normalized to isometric maximal voluntary contraction (MVC) amplitudes.

Results

With the exception of internal oblique and anterior deltoid for the horizontal condition, and erector spinae at L5 level for the vertical condition, the subject's posture had no effect on trunk muscular recruitment when using the oscillating blade. The vertical blade orientation resulted in higher amplitudes of spine rotation on the horizontal plane and produced the greatest activation levels of the internal oblique (47% MVC), pectoralis major (33% MVC), and external oblique (23% MVC). On the other hand, the horizontal orientation resulted in the greatest activation levels of erector spinae at T9 level (28% MVC), latissimus dorsi (26% MVC), and rectus abdominis (17% MVC).

Conclusions

Muscle activation and spine motion from using an oscillating blade were not affected by the standing or sitting posture of the subject. The choice of blade orientation was more important, because it defined the main group of muscles recruited during the exercise.

Key Words: Electromyography, Rehabilitation

Abbreviations: EMG, electromyography, EO, external oblique, ES, erector spinae, IO, internal oblique, LD, latissimus dorsi, MVC, maximal voluntary contraction, RA, rectus abdominis

LOW BACK DISORDERS are a major health problem in Western countries.¹ Some have been attributed to spinal instability.² Several devices have been purported to enhance stability by causing the cyclic activation of torso muscles, such as an oscillating pole.³ In particular, use of an oscillating blade has gained popularity as a tool in physical medicine clinics even though there are few data to guide its use. The tool requires the patient to generate oscillatory movements of the upper extremity, while the torso is braced to provide a stable foundation to the upper extremity. Because it is used with patients in both standing and sitting, we were motivated to document muscle activity during both postures.

In order to achieve oscillation at its natural frequency (4.5Hz), motion in the user's trunk and proximal arm must be minimized; excessive trunk or arm motion interferes with the coordination necessary to isolate reciprocal motions to the hand. Thus, it appears that the orientation, amplitude of oscillation, and specific technique when using the oscillating blade may either enhance or compromise spine stability. In a previous study, Moreside et al⁴ compared trunk muscle activation patterns between different oscillation amplitudes and blade orientations. Specific techniques performed with the oscillating blade in the upright position appeared to be more effective for recruiting the entire abdominal wall, latissimus dorsi, and erector spinae, all important spine stabilizers. However, there is a lack of studies dealing with the use of an oscillating blade in other orientations and postures, such as unsupported sitting.

Sitting postures are often adopted in the clinic, rightly or wrongly, for those with spine instability. Spine postures in trunk forward flexion,⁵ lateral flexion, and axial rotation⁶ differ between sitting and standing positions, with sitting positions showing higher ranges of spine motion in the 3 planes of movement. There are also differences in trunk muscle recruitment between the postures: for example, the erector spinae muscles are known to change their activation pattern during flexion-relaxation from a sitting position compared with standing.⁷ The objective of this study was thus to compare trunk muscle activation patterns and trunk kinematics when using the oscillating blade in standing and unsupported sitting postures, and to determine whether posture has any interaction effect with the different orientations of the device. Our hypothesis was that use of an oscillating blade in unsupported sitting will result in activation levels of the trunk muscles and lumbar motion parameters that are significantly different from those found in the upright position, and that the posture of the user will interact with the orientation of the device. This information would offer guidance for the clinician to achieve the desired activation patterns with a specific patient.

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Methods 

Subjects 

The participants in this study were 13 healthy men who were physically fit, recruited from a university population (age, 27.62±8.42y; height, 1.77±0.05m; mass, 75.91±8.05kg). All subjects were right-handed, without current back or shoulder pain. Participants completed a written informed consent document approved by the University of Waterloo Office for Research Ethics.

Tasks and Data Collection 

Participants were instructed as to the required activities, and allowed to practice until they were comfortable with their adeptness and coordination with the Bodyblade.^a They were then asked to oscillate the Bodyblade over a 15-second period in one of the following orientations: (1) a 2-handed vertical orientation of blade (medial-lateral oscillations), or (2) a 2-handed horizontal orientation of blade (up-down oscillations). Both exercises were performed both in an erect standing and an erect sitting position (as suggested by O'Sullivan et al⁸) (fig 1). The order of the exercises performed by the participants was randomized.

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• Fig 1. 

  Images of 1 subject using the Bodyblade: (A) erect standing with device in vertical orientation; (B) erect standing with device in horizontal orientation; (C) erect sitting with device in vertical orientation; (D) erect sitting with device in horizontal orientation. Note that the vertical orientation produces medial-lateral oscillations of blade in the frontal plane, whereas the horizontal orientation generates up-down oscillations in the sagittal plane.

Surface EMG signals were bilaterally collected on each subject (AMT-8 EMG system, with a common mode rejection ratio of 115dB at 60Hz, and input impedance of 10Giga Ω).^b The following trunk muscles and locations were used: RA, 3cm lateral to the umbilicus; EO, approximately 15cm lateral to the umbilicus; IO, halfway between the anterior superior iliac spine of the pelvis and the midline, just superior to the inguinal ligament; LD, lateral to T9 over the muscle belly; and ES at T9, L3, and L5 (T9ES, L3ES, and L5ES, respectively), located 5, 3, and 1cm lateral to each spinous process, respectively. EMG signals from the anterior deltoid muscle and the sternal portion of the pectoralis major muscle also were recorded on the right upper limb.

Pairs of silver-silver chloride surface electrodes (Kendall Meditrace 130)^c with a diameter of 1cm were positioned with an interelectrode distance of 3cm. The EMG signals were amplified to produce approximately ±2.5V, then A/D-converted (12-bit resolution) at 1024Hz. EMG signals were full-wave–rectified and low-pass–filtered (low-pass Butterworth filter) with a cutoff frequency of 2.5Hz and then normalized to isometric MVC amplitudes, which were obtained during isometric maximal exertion tasks, as explained elsewhere.⁴, ⁹ Normalization of the surface EMG signals to MVC amplitudes is a commonly used method to facilitate physiologic interpretation and for comparison between different subjects, different muscles, different electrodes sites on the same muscle, and different days.¹⁰, ¹¹ Although failure to obtain a “true” maximum exertion would introduce some level of experimental and interpretation error, steps were taken to avoid nonmaximum exertions: (1) 2 sets of 6 different maximal efforts were performed in the 3 cardinal planes for the trunk muscles,⁴, ¹¹ (2) subjects were verbally encouraged during the maximal exertions,¹¹, ¹² and (3) 2 experienced observers verified the correct performance of the MVC.

Throughout all activities, the spine position was measured using an electromagnetic tracking instrument (3-Space ISOTRAK),^d with measurements collected at a sampling frequency of 32Hz and synchronized to the EMG data. This instrument consists of an electromagnetic transmitter and 2 small receivers. The transmitter was strapped to the pelvis over the sacrum and one of the receivers on the ribcage, over the T12 spinous process. Thus, the relative lumbar motion about the flexion and extension, lateral bend, and twist axes was measured. All lumbar angular measurements were made relative to the standing anatomical position. Consequently, at any instant in time during the required exercises, the instantaneous spine position could be determined in 3 planes of motion relative to upright standing. The second receiver was positioned on the back of the right hand over the middle of the third metacarpal in order to measure the frequency, the amplitude, and the plane of the hand oscillations.

Data Analysis 

A single 2-second window was chosen from each trial that best represented the concurrent activity of all muscle groups during the requested Bodyblade activity. The 2-second window was deemed sufficient to capture about 10 cycles of oscillation (stationarity of the signal was assumed with 10 cycles). The mean activation level and lumbar angular displacement in the 3 planes of motion then was calculated for each window, and these calculations were averaged across all 13 subjects.

To assess the influence of the Bodyblade on muscle activation levels and lumbar angular displacement, a 2-way analysis of variance was conducted (SPSS for Windows, version 15.0).^e Two within-subjects variables were used for the analysis: posture, with 2 levels (sit and stand), and orientation, also with 2 levels (vertical and horizontal). In order to explore further the effects of the interaction between user's posture and orientation of the blade, post hoc paired t tests with a Bonferroni adjustment for alpha inflation were performed. An alpha level of .05 was considered significant for all analyses.

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Results 

Sitting or standing when performing the exercises had little effect on trunk muscular activation. However, a few exceptions were observed: for the horizontal condition, internal oblique showed greater activation in standing and anterior deltoid higher activation while seated; and for the vertical condition, ES at the L5 level showed higher activation in the seated position.

Spine rotation on the horizontal plane was significantly higher with a vertical orientation of the blade.

Trunk muscle activation patterns for the various positions tested are shown in figure 2, and the significant main effects by muscle and spine movement in table 1. The oscillation of a vertically oriented Bodyblade resulted in the greatest activation levels of the pectoralis major, internal oblique, and external oblique muscles (average amplitude 33%, 47%, and 23% of isometric MVC, respectively), whereas a horizontal orientation resulted in the greatest activation levels of the RA, LD, and T9 ES muscles (average amplitude 17%, 26%, and 28% of maximal voluntary isometric contraction, respectively). The magnitude of these changes was statistically significant for all muscle pairs.

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• Fig 2. 

  Averages and SDs of the mean normalized EMG amplitudes (%MVC) when using the Bodyblade in an erect standing or an erect sitting position, and with horizontal or vertical orientation of blade. Abbreviations: AD, anterior deltoid (dashed light gray block); PM, pectoralis major (dashed dark gray block).

Table 1. Significant Main Effects by Muscle and Spine Movement, Including F and P Values

Muscles and Spine Movement	Orientation		Posture		Significant Paired Comparisons (P<.05)
	F	P	F	P
RRA	15.902	.005	0.149	.711	Stand and sit: H>V
REO	22.750	.001	0.683	.432	Stand and sit: V>H
RIO	15.260	.008	6.651	.042	Sit: V>H; H: stand>sit
RLD	15.154	.003	4.597	.058	Stand and sit: H>V
RT9ES	14.898	.004	4.127	.073	Stand and sit: H>V
RL3ES	3.117	.115	0.079	.786	Sit: H>V
RL5ES	0.004	.953	3.594	.095	V: stand>sit
LRA	22.262	.001	0.076	.789	Stand and sit: H>V
LEO	146.785	<.001	0.158	.699	Stand and sit: V>H
LIO	49.680	<.001	9.241	.016	Stand and sit: V>H; H: stand>sit
LLD	4.870	.049	0.686	.425	Sit: H>V
LT9ES	20.061	.001	2.151	.173	Stand and sit: H>V
LL3ES	6.978	.025	0.004	.949	Sit: H>V
LL5ES	0.002	.965	9.984	.012	V: stand>sit
RAD	0.172	.687	3.032	.112	H: sit>stand
RPM	8.282	.015	<0.001	.995	Stand and sit: V>H
Flex	0.472	.518	0.530	.494
Bend	5.925	.093	0.016	.907
Twist	9.663	.036	1.524	.285	Stand and sit: V>H

NOTE. Orientation of the blade variable: vertical (V) vs horizontal (H); posture of the user: stand versus sit.

Abbreviations: AD, anterior deltoid; Bend, rotation on the coronal plane; Flex, rotation on the sagittal plane; L, left; PM, pectoralis major; R, right; Twist, rotation on the horizontal plane.

*Significant main effect (P<.05).

When comparing right and left sides, all muscles demonstrated near-equal activation levels side to side (see fig 2). Figure 3 shows the normalized EMG amplitudes of the right IO and EO during a 2-second window of the standing position, vertical orientation of the blade trial, whereas figure 4 shows EMG amplitudes of the right RA and ES during a 2-second window of the standing position, horizontal orientation, from a typical subject. These figures illustrate the time histories of muscle co-contraction during typical Bodyblade trials, showing the antiphasic nature of the muscle pairing: muscles act in pairs, RA and ES when the blade is horizontally oriented and the opposite obliques when the blade oscillates vertically.

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• Fig 3. 

  Vertical stand. Normalized EMG time histories of 1 typical subject for right IO (black line) and right EO (gray line) during use of the Bodyblade in standing with a vertical orientation of blade. Notice the antiphasic coactivity between the IO and EO signals.

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• Fig 4. 

  Horizontal stand. Normalized EMG time histories of 1 typical subject for right ES at T9 (black line) and right RA (gray line) during use of the Bodyblade in standing with a vertical orientation of blade. This is an example of the antiphasic manner in which subjects recruited the T9 ES and RA.

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Discussion 

The results support partially our hypothesis: they show that there are differences in the activation levels of the trunk muscles and lumbar motion parameters between different orientations of the Bodyblade, but there is almost no interaction with the posture of the user. This implies that the sitting or standing posture does not change muscle activation magnitude or patterns, thus the clinician may choose either posture based on patient tolerance. Clearly, the crucial factor that influences muscle activation pattern is the orientation of the device. Further, the use of the Bodyblade does not involve large motions of the spine because the neutral posture is best preserved in the standing posture. Suni et al¹³ noted that controlling the spine neutral zone posture is a specific form of exercise that has potential for prevention of recurrent low back pain.

The results from this study compare to the findings of Moreside et al,⁴ who showed greater activation levels for bilateral IO and EO with a vertical use of the Bodyblade, whereas a horizontal use of the Bodyblade resulted in RA and T9 ES having the highest activation levels. This makes logical sense given that the vertical orientation produces twisting torque while the horizontal orientation produces sagittal torque. These muscles have an antiphasic co-contraction pattern that depends on the orientation of the blade: longitudinal muscles with vertically oriented fibers (RA and ES) co-contract antiphasically when the blade is horizontally oriented, and oblique muscles (IO and EO) when the blade oscillates vertically. Thus, a clinician is able to target specific muscle groups with manipulation of blade orientation and influence specific modes of joint stabilization.

Callaghan and McGill¹⁴ found little difference in trunk muscular activation profiles between sitting and standing positions, which appears also to be the case when using the Bodyblade. In the present study, the most important effect of user's posture on muscle recruitment was shown by the IO muscles, which were more active when the user adopted a standing position. Although in their work there was no direct comparison between standing and sitting, O'Sullivan et al⁸ showed higher levels of IO activity in erect standing than erect sitting positions, probably to hold the abdominal contents. Nevertheless, in our study this effect was only significant with a horizontal orientation of the Bodyblade. This could be explained by the important increase in activity of the IO muscles when the blade was vertically oriented (the difference in IO activation between both blade orientations was more than 20% of IO MVC), which could be hiding the effect of posture. That is, a vertical orientation of the blade produces high levels of contraction of the IO, irrespective of the user's posture. Further, one of the effects of the oblique muscle co-contraction is to brace the spine and reduce axial rotation,¹⁵ so an increase in oblique muscle activity is probably a response to the need to control the twisting effect of the vertical blade oscillation.

Study Limitations 

The data of this study provides an insight into trunk muscle recruitment when using the Bodyblade in standing and unsupported sitting postures and with 2 different orientations of the blade. As such, it may help clinicians to achieve desired activation patterns by altering exercise posture and blade orientation. However, the interpretation of our results is limited to subjects who are healthy and relatively physically fit. We should also take into account that the Bodyblade can be used in other body postures, with 1 or 2 hands, with various orientations of the blade, and with varying amplitudes of oscillation. Further investigations are required to investigate the trunk muscular response and the spine stability of patients with low back disorders when using the Bodyblade in exercises and conditions that differ from the ones used in this study. It would have been interesting to assess whether muscle fatigue changes the results. However, EMG frequency measures of fatigue during dynamic contractions are problematic,¹⁶ and the oscillatory nature of the EMG signals observed here would probably not have yielded valid results. Another limitation of the present study is the great amount of dependent variables that were analyzed in a sample population of 13 subjects, which increases the risk for familywise error rates. It may be worthwhile to test with more subjects in the future.

Finally, we cannot discount the possibility that cross-talk between trunk muscles could have affected our surface EMG recordings on the trunk, despite the fact that we followed previous recommendations on electrode placement in order to obtain a precise representation of each muscle.¹⁷ Moreover, after electrode placement, subjects were asked to perform trunk movements in all directions to check the detection of an appropriate signal.

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Conclusions 

Muscle recruitment and spine kinematics when using the Bodyblade are not affected by the standing or sitting posture of the user. The choice of blade orientation is more important, because it will determine the main group of muscles recruited during the exercise. Future studies should consider use of the Bodyblade in other postures, such as 3-point kneeling, to test further the effect that changing the body's position has on muscle recruitment and spine kinematics. In this way, clinicians will be enabled to choose the most appropriate positions of exercise for their patients.

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• a Bodyblade/Hymanson Inc, PO Box 5100, Playa del Rey, CA 90296.
• b Bortec Biomedical Ltd, 239 Springborough Way, Calgary, AB, Canada T2H 5M8.
• c Tyco Healthcare Group LP, 15 Hampshire St, Mansfield, MA 02048.
• d Polhemus Inc, 40 Hercules Dr, PO Box 560, Colchester, VT 05446.
• e SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.