PM R 7 (2015) 479-484
www.pmrjournal.org
Original Research
Difference in Selective Muscle Activity of Thoracic Erector Spinae During Prone Trunk Extension Exercise in Subjects With Slouched Thoracic Posture Kyung-hee Park, PhD, PT, Jae-seop Oh, PhD, PT, Duk-hyun An, PhD, PT, Won-gyu Yoo, PhD, PT, Jong-man Kim, PhD, PT, Tae-ho Kim, PhD, PT, Min-hyeok Kang, MSc, PT
Abstract Background: The prone trunk extension (PTE) exercise is often used to strengthen the back extensors. Although altered trunk
posture is associated with movement impairment, the influences of a slouched thoracic posture on muscle activity of the thoracic erector spinae and thoracic movement during the PTE exercise were overlooked in previous studies. Objectives: To compare the muscle activity of the erector spinae muscles and the relative ratio of the thoracic and lumbar erector spinae muscles during a PTE exercise in subjects with and without slouched thoracic posture. Design: Cross-sectional. Setting: University motion analysis laboratory. Participants: The study included 22 subjects with slouched thoracic posture (defined as 40 ) and 22 age- and gender-matched healthy subjects. Methods: All participants performed the PTE exercise. Main outcome outcome measures: measures: Bilateral surface electromyographic signals of the longissimus thoracis, iliocostalis lumborum pars thoracis, and pars lumborum muscles were measured during PTE exercises. Thoracic kyphosis (the angle of T1 minus T12) and lumbar lordosis (absolute value of the angle of L5 minus T12) were recorded using inclinometers during the PTE exercise. Results: The results showed no difference in muscle activity of the erector spinae in subjects with slouched thoracic posture versus those without during the PTE exercise. However, selective recruitment of the erector spinae pars thoracis was decreased significantly, and the thoracic kyphotic angle and lumbar lordotic curve were increased, during the PTE exercise in subjects with a slouched posture. Conclusions: Although the PTE exercise has historically been a key component of correction of hyperkyphosis, the increased spinal curvature inhibits muscle activation of the erector spinae pars thoracis in these individuals, thus limiting effective strength gains. Therefore, modified methods to maintain a neutral posture of the spine and facilitate muscle activation of the erector spinae pars thoracis are needed in these individuals.
Introduction
A slouch slouched ed postu posture re is commo commonly nly involv involved ed in daily daily sitt sittin ingg acti activi viti ties es and and is defin defined ed as a rela relaxe xed d sitti sitting ng posture with a flexed thoracic and lumbar spine [1,2] [1,2].. An increased or prolonged slouched posture may cause not not only only low-ba low-back ck pain pain (LBP) (LBP) and and mo movem vement ent-re -relat lated ed disorders in the lumbar spine, but it may also result in thoracic spine pain or movement impairment syndrome
such such as thorac thoracic ic flexio flexion n syndro syndrome me [3] [3],, osteoporo osteoporotic tic compression fractures of the spine [4] [4],, or impairment of shoulder flexion due to disturbances in scapular movement [5,6]. [5,6]. It is like likely ly bene benefic ficia iall to stre streng ngth then en the the thor thorac acic ic spin spine e exte extens nsor orss and and to corr correc ectt exce excess ssiv ive e thoracic thoracic kyphosis to reduce reduce or prevent prevent painful painful spinal disorders and other complications [3,7] [3,7];; however, few research studies have examined the thoracic versus the lumbar spine.
1934-1482/$ - see front matter ª 2015 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j http://dx.doi.org /10.1016/j.pmrj.2014.10 .pmrj.2014.10.004 .004
480
Muscle Activity of Thoracic Erector Spinae
The prone trunk extension (PTE) exercise is a familiar technique used to strengthen the erector spinae in the treatment of weak and fatigue-sensitive back musculature; this exercise is typically recommended to prevent the natural progression of kyphosis [7]. However, it is questionable whether the PTE exercise is always effective in individuals with a slouched thoracic posture [8-11]. A prolonged slouched posture has a tendency to induce excessive thoracic kyphosis according to the directional susceptibility of movement [8]. Moreover, a prolonged slouched posture may lengthen or stretch the erector spinae, which may decrease the position sense [1,9,10]. The movements used in an attempt to decrease the thoracic curve may cause pain or difficulty and may produce compensatory changes in the more mobile lumbar region [3,11]. Therefore, lumbar extension may be performed to a greater degree than thoracic extension in these individuals during PTE exercises, and lumbar hyperextension exercises accompanied by inordinate use of the lumbar erector spinae musculature seem to be related to LBP due to abnormal compressive and shear forces [12-16]. Therefore, very careful observation and posture correction are crucial to prevent hyperextension of the lumbar spine and to facilitate the thoracic erector spinae muscles in such patients during PTE exercises. Although synergistic activity of the erector spinae pars thoracis and lumborum muscles is considered the main mechanism of trunk extension, these muscles do not comprise a homogeneous muscle mass, but have anatomical and functional differences [17-20]. Knowledge of the activity of the erector spinae in individuals with slouched thoracic posture during PTE exercises is insufficient. The purpose of our research was to compare the muscle activity of the erector spinae pars thoracis and lumborum muscles and the relative ratio of the thoracic and lumbar erector spinae muscles in subjects with a slouched thoracic posture. Because muscle activity of the erector spine influences trunk posture, a secondary purpose was to compare thoracic kyphosis and lumbar lordosis in subjects with and without slouched thoracic posture during the PTE exercise. Methods
Study Participants
In total, 22 subjects (10 male and 12 female) with thoracic slouched posture and 22 healthy subjects (10 male and 12 female) were selected from among 250 young persons engaged in desk work and computer use for more than 5 hours per day. Participants with metabolic, neuromuscular, or musculoskeletal disorders or a history of spinal surgery were excluded. In the 22 subjects with slouched thoracic posture, the thoracic spine alignment tended to demonstrate excessive thoracic kyphosis in a self-selected, relaxed standing position.
These subjects were selected from among 250 young persons at 3 universities in South Korea. The criteria used to place the subjects into the slouched thoracic posture and control groups were based on data taken from 250 young persons whose mean kyphotic angle in a relaxed standing posture was 30.2 (standard deviation [SD], 4.83 ). The slouched thoracic posture group was defined as those subjects with a kyphotic angle 40 , which represented the group’s mean plus 2 SDs (30.2 þ [2 4.83 ]) [21]. A total of 22 age- and gender-matched participants with a kyphotic angle within the range of mean 1 SD were selected as the control group. These participants reported no instance of LBP or thoracic pain within the last year, no musculoskeletal disorders that would limit normal thoracic kyphosis, and no pain during the test procedure. This study was approved by the human subjects committee of the University of Inje. Informed consent was obtained from all subjects. Instrumentation
The angles of thoracic kyphosis and lumbar lordosis during the PTE exercise were measured using 2 gravitydependent inclinometers (Zebris Medical GmbH, Isny, Germany). The spinous processes of the first thoracic vertebra (T1), twelfth thoracic vertebra (T12), and fifth lumbar vertebra (L5) were used as landmarks for positioning the inclinometer sensors [6] (Figure 1). These spinal levels were marked by palpation; the L5 spinous process was identified above the sacrum, the T12 spinous process was identified superiorly from the L5 point, and the T1 spinous process was identified inferiorly from the seventh cervical vertebra (designated as the most prominent spinal process) [6]. During PTE exercise, the angle between T1 and T12 and between L5 and T12 were measured to assess thoracic kyphosis and lumbar lordosis, respectively, using the inclinometers. Surface electromyographic (EMG) signals were recorded for each subject using 8 preamplified (gain: 1000) active surface electrodes (model DE-2.3; Delsys, Inc., Wellesley, MA). EMG signals from the recording sites were band-pass filtered between 20 and 450 Hz, analogto-digital converted at a sampling rate of 2048 Hz, and stored on a computer hard disk for later analysis. The electrodes were positioned bilaterally on the iliocostalis lumborum pars lumborum (right ICL and left ICL) at the L3 level, midway between the lateral-most
Figure 1. Placements of the inclinometers.
481
K. Park et al. / PM R 7 (2015) 479-484
palpable border of the erector spinae and a vertical line through the posterosuperior iliac spine [17,19,22];onthe longissimus thoracis (right LT and left LT) at the T9 level, midway between a line through the spinous process and a vertical line through the posterosuperior iliac spine, located approximately 5 cm laterally [19,22]; and on the iliocostalis lumborum pars thoracis (right ICTand left ICT) at the T10 level, midway between the lateral-most palpable border of the erector spinae and a vertical line through the posterosuperior iliac spine [17,23-25]. Skin impedance was reduced by shaving excess body hair if necessary, by gently abrading the skin with finegrade sandpaper, and wiping the skin with alcohol swabs. Procedures
The subjects were asked to perform a body weight edependent isometric back extension exercise in the prone position. The PTE exercise was performed with the iliac crests aligned with the table edge and the subjects’ arms crossed at the chest and lower limbs fixed by nonelastic straps at the hip, knees, and ankles. While looking downward at a visual fixation point, the subjects were instructed to raise their trunk to horizontal (parallel to the ground) and maintain this position for 5 seconds [26] (Figure 2). The exercises were taught to each subject before data collection; 2 practice sessions were allowed to achieve proper performance. A bar indicator was positioned approximately at the T6 level for feedback about the horizontal position. The procedure was repeated 3 times with a 3-minute recovery period between trials. The maximum voluntary isometric contraction (MVIC) of the erector spinae was used for normalization. To measure the MVIC of the ES pars thoracis and lumborum, the subjects, lying in a prone position, placed their hands on their head with their legs strapped to the table. Back extension was performed with maximum isometric effort against resistance by the experimenter on the angular inferior aspect of both scapulae [18,25]. This was repeated 3 times, with a 30-second rest period between sessions. A root mean square (RMS) processing method was executed on 250-millisecond (512 points) successive time windows; EMG signals from the 3 middle seconds of the 5-second isometric contraction during the PTE exercise and MVIC testing were used. The data obtained were normalized (% MVIC) by the mean RMS value during
MVIC testing. The normalized LT:ICL and ICT:ICL ratios were calculated to measure the selective recruitment of the thoracic erector spinae. Inclinometer markers to compare the angles of thoracic kyphosis and lumbar lordosis were placed over T1, T12, and L5 and were simultaneously measured in the isometric PTE position with a surface EMG signal. In a previous study, intrarater and interrater reliability were concurrently established during PTE exercises in 15 participants and were found to be highly correlated (intraclass correlation coefficient [ICC] [1,2] ¼ 0.97, ICC [2,1] ¼ 0.91). Clockwise rotation of the indicator (toward the extension direction) represented positive values, and the opposite rotation represented negative values. The angle of T1 minus T12 was the value of thoracic kyphosis, and the absolute value of the angle of T12 minus T1 was the angle of thoracic extension. The angle of lumbar lordosis was the absolute value of the angle of L5 minus T12. Statistical Analysis
The Kolmogorov eSmirnov test was used to assess homogeneity of variance of the % MVIC of each muscle and the LT:ICL and ICT:ICL ratios. An independent t -test was performed to evaluate the differences between the right and left erector spinae EMG data. Because no significant differences were found, EMG data of the right and left erector spinae were averaged and are reported. Independent t-tests were then performed to investigate the effect of slouched thoracic posture on the normalized EMG activity of the erector spinae (% MVIC), the selective recruitment of the thoracic erector spinae (LT:ICL and ICT:ICL ratios), the angle of thoracic kyphosis in a standing posture, and the angle of thoracic kyphosis and the angle of lumbar lordosis during the PTE exercise. All statistical analyses were performed with the statistical software package SPSS version 18.0 (SPSS Inc., Chicago, IL), and the level of statistical significance was set at P < .05. Results
The subjects in the slouched thoracic posture group were a mean ( SD) age of 27.54 4.29 years; their mean height was 169.37 8.57 cm, body weight 63.25 8.79 kg, and thoracic kyphotic angle 44.25 4.14 while standing (Table 1). The subjects in the control Table 1
Thoracic kyphotic angles in subjects with and without slouched thoracic posture in a standing posture
Figure 2. Prone trunk extension exercise.
With Slouched Posture (n ¼ 22)
Without Slouched Posture (n ¼ 22)
P Value
44.25 4.14
30.05
<
4.72
Data for angles are given in degrees ( ).
.001
482
Muscle Activity of Thoracic Erector Spinae
Table 2
Differences in normalized EMG activity of each segment in the erector spinae muscles and selective recruitment of the longissimus thoracis and iliocostalis pars thoracis to iliocostalis pars lumborum during the PTE exercise in participants with and without a thoracic slouched posture Variable
Muscles
With Slouched Posture
Without Slouched Posture
P Value
Muscle activity (% MVIC)
Both LT Both ICT Both ICL Both LT Both ICT
37.80 40.93 56.28 0.72 0.78
37.84 39.48 52.36 0.82 0.88
.933 .701 .151 .040* .024*
Ratio to ICL
14.52 18.38 21.90 0.25 0.20
EMG ¼ electromyography; PTE ¼ prone trunk extension; LT ¼ longissimus thoracis; MVIC ICT ¼ iliocostalis lumborum pars thoracis; ICL ¼ iliocostalis lumborum pars lumborum. P < .05.
16.51 20.91 22.75 0.37 0.31
¼ maximum
voluntary isometric contraction;
*
group were a mean ( SD) age of 26.15 5.34 years; their mean height was 168.25 7.46 cm, body weight 61.92 9.17 kg, and thoracic kyphotic angle 30.05 4.72 while standing (Table 1). No difference in the muscle activity of the erector spinae (% MVIC) was found between the 2 groups, but significant differences in both LT:ICL and ICT:ICL ratios between the groups were found during PTE exercise. The LT:ICL and ICT:ICL ratios were significantly lower in the slouched thoracic posture group (0.72 0.25 and 0.78 0.20, P ¼ .040 and .024, respectively) than in the control group (0.82 0.37 and 0.88 0.31, respectively) (Table 2). In the slouched thoracic posture group, the upper thoracic spine (T1) was significantly flexed 3.83 8.03 (P < .001), and the lower thoracic spine (T12) was significantly extended 12.17 7.70 (P ¼ .026), but the extension movement of L5 during the PTE exercise was not significantly different between groups ( P ¼ .666) during the PTE exercise. Kyphosis of the thoracic spine and lordosis of the lumbar spine were significantly higher at 16.00 10.36 and 25.13 6.30 , respectively, in the slouched thoracic posture group than in the control group during PTE exercise (7.21 9.90 and 22.05 7.20 ; P <.001 and .045, respectively) (Table 3). Discussion
The present study was designed to investigate the influence of slouched thoracic posture on the level of activity (%MVIC) of the erector spinae muscles (pars thoracis and lumborum), the balance between these
erector spinae muscles (LT:ICL and ICT:ICL ratios), and thoracic and lumbar spine movements during PTE exercise. Although there was no difference in the muscle activity of the erector spinae muscles in subjects with and without a slouched thoracic posture, a significant decrease in the relative ratio of the thoracic to lumbar erector spinae muscles was found in the slouched posture group versus the control group. In addition, the thoracic kyphotic angle and lumbar lordotic curve were greater during the PTE exercise in these subjects than in the control group. An increased kyphoticelordotic curve of the spine could be explained by the decreased activity of the erector spinae pars thoracis and increased activity of the erector spinae pars lumborum. Although the erector spinae pars thoracis and lumborum produce forces synergistic with the trunk extension force, the lumbar extensors are more naturally suited to spinal stability; the thoracic extensors, located more superficially, are designed for higher loads [13,18,19]. Our results showed no significant difference in muscle activity itself, but the LT:ICL and ICT:ICL ratios were decreased in the slouched posture group. To the best of our knowledge, few studies have investigated the activities of the LT and ICT during extension exercises or their activity relative to that of the ICL. The level of erector spinae pars thoracis muscle activity (37%e41% MVIC) in the current study was lower than that in previous studies (41%e74% MVIC) [12,18,22]. The muscle activity of the erector spinae pars lumborum in the current study was 52%e56% MVIC, which is similar to some previous results (55%e57% MVIC) [12,22] and lower than others
Table 3
Differences in thoracic and lumbar spine movement during the PTE exercise in participants with and without habitual slouched posture Degree of Trunk Extension ( ) Variable T1 T12 L5 Kyphosis of thoracic spine Lordosis of lumbar spine PTE ¼ prone trunk extension. P < .05. *
With Slouched Posture 3.83 8.03 12.17 7.70
11.95 6.40 16.00 10.36 25.13 6.30
Without Slouched Posture 2.98 9.95 10.20
3.85 11.85 7.01 7.21 9.90 22.05 7.20
P Value
.001* .026* .666 <.001* .045* <
K. Park et al. / PM R 7 (2015) 479-484
(70% MVIC) [18]. The main reason for this is that the PTE exercise was performed in a different way in the previous studies, with both arms raised to the head instead of folded at the chest or with participants instructed to achieve an intensity of 60% of 1 repetition maximum (RM). Notably, the muscle activity of the erector spinae pars thoracis in the slouched thoracic posture group was lowest, and decreased activation was not enough to straighten the thoracic spine. The PTE exercise is beneficial in strengthening the erector spinae for the treatment of weak and fatigue-sensitive back musculature [7]. However, an appropriate spinal curve should be considered when performing the PTE exercise, because maintenance of a stable neutral zone in the spine is assumed to be safe and to diminish the stress on the spine [12,22,27]. That is, the PTE exercise with increased thoracic kyphosis and lumbar lordosis may be less effective and may produce pain because of greater disk loading, compression force, and shearing force caused by an increased spinal curve in the sagittal plane [28,29]. In the present study, the slouched thoracic posture group showed increases in the lumbar lordotic and thoracic kyphotic curves during the PTE exercise. Considering directional susceptibility to movement, namely, compensatory movement in a specific direction or a stress applied in a specific direction [8], persons with slouched thoracic posture are accustomed to a thoracic flexed posture not only during standing but also during other positions, and even during the PTE exercise. Also, thoracic kyphosis in a relaxed standing posture was greater in the slouched thoracic posture group than in the control group in this study. It is inferred that soft tissues allow greater flexibility, together with less stiffness, going into thoracic flexion in the slouched thoracic posture group than in the control group, which may lead to a greater thoracic kyphotic angle in the slouched thoracic posture group, even with no significant difference in muscle activity of the erector spinae between the groups during the PTE exercise. Individuals with a slouched thoracic posture have decreased thoracic extension range of motion [11,30] and may compensate for this by increasing their lumbar lordotic curve instead of increasing thoracic extension during the PTE task. Considering the greater thoracic kyphotic angle in the slouched thoracic posture group than in the control group, individuals with a slouched thoracic posture may have a mechanical disadvantage in recruiting the thoracic extensor muscles. Thus, insufficient thoracic extensor strength and abnormal neuromuscular control could be important issues in persons with a slouched thoracic posture, although these were not addressed in this study. In addition, a habitually flexed posture lengthens the intrafusal fibers of the paraspinal muscles and intervertebral ligaments, thereby stretching the g-motor neuron and mechanoreceptors, causing diminished position sense in the
483
spine [1,9]. Thus, these individuals may also have difficulty recognizing their abnormal movement patterns and correcting their increased thoracic kyphosis and lumbar lordosis angles to achieve a neutral curve [30]. The first limitation of the current study is that we examined a young healthy population; thus, the results cannot be generalized to elderly individuals or to patients with LBP. Second, only a single exercise (PTE) was used. Third, although the main function of the erector spinae is to maintain an erect posture, the endurance of the erector spinae muscles was not tested. Future research should use various exercises and resistances and compare the muscle endurance of the erector spinae muscles in individuals with and without slouched thoracic posture. In addition, differences in the diameter and contractility of erector spinae muscles between persons with and without a slouched thoracic posture should be measured using real-time ultrasound in a future study. Finally, we measured only the thoracic kyphotic angle in this study. To fully understand thoracic mobility and the influence of thoracic kyphosis on adjacent joints, the mobility of the rib cage and thoracic facet joints and the alignment of the craniocervical junction should also be assessed in future studies. Conclusion
In this study the muscle activity relative ratio of the thoracic to lumbar erector spinae muscles decreased significantly, whereas the angle of kyphosis and lumbar lordosis increased significantly, during the PTE exercise in the slouched thoracic posture group compared with the control group. The increased spinal curve in the sagittal plane and decreased selective activation of the erector spinae pars thoracis induced during this exercise could have a negative impact on the spine. Thus, careful observation and modified methods (eg, support of the lower trunk to prevent compensatory lumbar lordosis) to maintain a neutral posture of the spine and to facilitate muscle activation of the erector spine pars thoracis are needed in these individuals. References 1. Dolan KJ, Green A. Lumbar reposition sense: The effect of a ‘slouched’ posture. Man Ther 2006;11:202-207 . 2. Kendall FP, Provance PG, McCreary EK. Muscles: Testing and Function. 4th ed. Baltimore: Williams & Wilkins; 1993 . 3. Sahrmann SA. Movement System Impairment Syndromes of the Extremities, Cervical and Thoracic Spine. St. Louis, MO: Mosby; 2010. 4. Brigg AM, Bragge P, Smith AJ, Govil D, Straker LM. Prevalence and associated factors for thoracic spine pain in the adult working population: A literature review. J Occup Health 2009;51:177-192 . 5. Crosbie J, Kilbreath SL, Dylke E, et al. Effects of mastectomy on shoulder and spinal kinematics during bilateral upper-limb movement. Phys Ther 2010;90:679-692 .
484
Muscle Activity of Thoracic Erector Spinae
6. Lewis JS, Valentine RE. Clinical measurement of the thoracic kyphosis. A study of the intra-rater reliability in subjects with and without shoulder pain. BMC Musculoskel Disord 2010;11:39-46 . 7. Ball JM, Gagle P, Johnson BE, Lucasey C, Lukert BP. Spinal extension exercises prevent natural progression of kyphosis. Osteopjoros Int 2009;20:481-489. 8. Sahrmann SA. Diagnosis and Treatment of Movement System Impairment Syndrome. St. Louis, MO: Mosby; 2002 . 9. Cao DY, Pickar JG. Lengthening but not shortening history of paraspinal muscle spindles in the low back alters their dynamic sensitivity. J Neurophysiol 2011;105:434-441 . 10. Ge W, Pickar JG. Time course for the development of muscle history in lumbar paraspinal muscle spindles arising from changes in vertebral position. Spine J 2008;8:320-328 . 11. Edmondstone SJ, Singer KP. Thoracic spine: Anatomical and biomechanical considerations for manual therapy. Man Ther 1997; 2:132-143. 12. Callaghan JP, Gummomg JL, McGill SM. The relationship between lumbar spine load and muscle activity during extensor exercise. Phys Ther 1998;78:8-18. 13. Panjabi M, Abumi K, Duranceau J, Oxland T. Spinal stability and intersegmental muscle forces: A biomechanical model. Spine 1989; 14:194-200. 14. Panjabi MM. The stabilizing system of the spine. Part 1. Function, dysfunction, adaptation, and enhancement. J Spinal Disorders 1992a;5:383-389 . 15. Renkawitz T, Boluki D, Grifka J. The association of low back pain, neuromuscular imbalance, an trunk extension strength in athletes. Spine J 2006;6:673-683. 16. Renkawitz T, Linhardt O, Grifka J. Electric efficiency of the erector spinae in high performance amateur tennis palyers. J Sports Med Phys Fitness 2008;48:409-416. 17. Coorevits P, Danneels L, Cambier D, Ramon H, Vandertraeten G. Assessment of thevalidityof theBiering-Sorensentest for measuring backmusclefatigue based on EMGmedianfrequency characteristics of back and hip muscles. J Electromyogr Kinesiol 2008;18:997-1005. 18. De Ridder E, Van Oosterwijck JO, Vleeming A, Vanderstraeten GG, Danneels LA. Posterior muscle change activity during various
extension exercises: An observational study. BMC Musculoskelet Disord 2013;14:204. 19. Panjabi MM. The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. J Spin Disord 1992b;5:390-396 . 20. Boseker EH, Moe jH, Winter RB, Koop SE. Determination of “normal” thoracic kyphosis: A roentgenographic study of 121 “normal” children. J Pediatr Orthop 2000;20:796-798 . 21. Macintosh JE, Bogduk N. The morphology of the lumbar erector spine. Spine 1987;12:658-668. 22. Macintosh JE, Bogduk N. The attachments of the lumbar erector spinae. Spine 1991;16:783-792. 23. Da Silva R, Larivie ´re C, Arsenault B, Nadeau S, Plamondon A. Effect of pelvic stabilization and hip position on trunk extensor activity during back extension exercises on a Roman chair. J Rehabil Med 2009;41:136-142. 24. McGill SM. Low back exercise: Evidence for improving exercise regimens. Phys Ther 1998;78:754-765 . 25. Vera-Garcia FJ, Moreside JM, McGill SM. MVC techniques to normalize trunk muscle EMG in healthy women. J Electromyogr Kinesiol 2010;20:10-16. 26. Demoulin C, Vanderthommen M, Duysens C, Crielaard JM. Spinal muscle evaluation using the Sorensen test: A critical appraisal of the literature. Joint Bone Spine 2006;73:43-50 . 27. Colado JC, Pablos C, Chulvi-Medrano I, Garcia-Masso X, Flandez J, Behm DG. The progression of paraspinal muscle recruitment intensity in localized and global strength training exercise is not based on instability alone. Arch Phys Med Rehabil 2011;92: 1875-1883. n JH, Wrigley TV, et al. Thoracic kyphosis af28. Briggs AM, van Die e fects spinal loads and trunk muscle force. Phys Ther 2011;85: 595-607. 29. Harrison DE, Colloca C, Harrison DD, Janik TJ, Haas JW, Keller TS. Anterior thoracic posture increases thoracolumbar disc loading. Eur Spine J 2005;14:234-242. 30. Edmondston SJ, Waller R, Vallin P, Holthe A, Noebaer A, King E. Thoracic spine extension mobility in young adults: Influence of subject position and spinal curvature. J Orthop Sports Phys Ther 2011;41:266-273.
Disclosure K.P. Department of Physical therapy, Masan University, Changwon, South Korea
J.K. Department of Physical Therapy, Jeonju Univerisy, Jeonju, South Korea
Disclosure: nothing to disclose
Disclosure: nothing to disclose
J.O. Department of Physical Therapy, College of Biomedical Science and Engi-
T.K. Department of Physical Therapy, Daegu University, Daegu, South Korea
neering, INJE University 607 Obang-dong, Gimhae-si, Gyeongsangnam-do, South Korea, 621-749. Address correspondence to: J.-s.O.; e-mail:
[email protected] Disclosure: nothing to disclose
Disclosure: nothing to disclose
D.A. Department of Physical Therapy, INJE University, Gimhae, South Korea
Disclosure: nothing to disclose W.Y. Department of Physical Therapy, INJE University, Gimhae, South Korea
Disclosure: nothing to disclose
M.K. Department of Physical Therapy, Graduate School, INJE University,
Gimhae, South Korea Disclosure: nothing to disclose Submitted for publication March 17, 2014; accepted October 5, 2014.
