PM R XXX (2014) 1-6
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 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 slouched posture is commonly involved in daily sitting activities and is defined as a relaxed sitting posture with a flexed thoracic and lumbar spine [1,2]. An increased or prolonged slouched posture may cause not only low-back pain (LBP) and movement-related disorders in the lumbar spine, but it may also result in thoracic spine pain or movement impairment syndrome
such as thoracic flexion syndrome [3], osteoporotic compression fractures of the spine [4], or impairment of shoulder flexion due to disturbances in scapular movement [5,6]. It is likely beneficial to strengthen the thoracic spine extensors and to correct excessive thoracic kyphosis to reduce or prevent painful spinal disorders and other complications [3,7]; however, few research studies have examined the thoracic versus the lumbar spine.
1934-1482/$ - see front matter ª 2014 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2014.10.004
2
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.
K. Park et al. / PM R XXX (2014) 1-6
palpable border of the erector spinae and a vertical line through the posterosuperior iliac spine [17,19,22]; on the 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 ICT and 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 weightedependent 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
3
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 KolmogoroveSmirnov 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
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 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 slouched posture is commonly involved in daily sitting activities and is defined as a relaxed sitting posture with a flexed thoracic and lumbar spine [1,2]. An increased or prolonged slouched posture may cause not only low-back pain (LBP) and movement-related disorders in the lumbar spine, but it may also result in thoracic spine pain or movement impairment syndrome
such as thoracic flexion syndrome [3], osteoporotic compression fractures of the spine [4], or impairment of shoulder flexion due to disturbances in scapular movement [5,6]. It is likely beneficial to strengthen the thoracic spine extensors and to correct excessive thoracic kyphosis to reduce or prevent painful spinal disorders and other complications [3,7]; however, few research studies have examined the thoracic versus the lumbar spine.
1934-1482/$ - see front matter ª 2014 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2014.10.004
2
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.
K. Park et al. / PM R XXX (2014) 1-6
palpable border of the erector spinae and a vertical line through the posterosuperior iliac spine [17,19,22]; on the 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 ICT and 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 weightedependent 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
3
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 KolmogoroveSmirnov 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
