Manual Therapy xxx (2013) 1e6
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Original article
Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals Hyun-ju Park a, Duck-won Oh b, *, Suhn-yeop Kim c a
Department of Physical Therapy, The Graduate School, Daejeon University, 96-3, Yongun-dong, Dong-gu, Daejeon, 300-716, Republic of Korea Department of Physical Therapy, College of Health Science, Cheongju University, 298 Daeseongro, Sangdang-gu, Cheongju, Chungbuk, 360-764, Republic of Korea c Department of Physical Therapy, College of Natural Science, Daejeon University, 96-3, Yongun-dong, Dong-gu, Daejeon, 300-716, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 February 2013 Received in revised form 24 October 2013 Accepted 1 November 2013
This study aimed to identify the electromyographic (EMG) effects in selected trunk muscles after incorporating hip movement into bridging exercise. Twenty-six healthy adults (13 men and 13 women) volunteered for this experiment. EMG data (% maximum voluntary isometric contraction) were recorded from the rectus abdominis (RA), obliquus internus (OI), erector spinae (ES), and multifidus (MF) muscles of the dominant side while the subjects performed 3 types of bridging exercise, including bridging alone (Bridging 1), bridging with unilateral hip movements (Bridging 2), and bridging with bilateral hip movements (Bridging 3) in a sling suspension system. The RA and OI showed greater EMG activity during Bridging 2 and 3 compared to Bridging 1, with the greatest OI activity during Bridging 3 (p < 0.05), and the activity of the MF appeared to be greater during Bridging 3 than during Bridging 1 and 2 (p < 0.05). Furthermore, the OI/RA and MF/ES ratios were significantly higher for Bridging 2 (OI/RA ¼ 1.89 1.41; MF/ES ¼ 1.03 0.19) and Bridging 3 (OI/RA ¼ 2.34 1.86; MF/ES ¼ 1.03 0.15) than Bridging 1 (IO/ RA ¼ 1.35 0.92; MF/ES ¼ 0.98 0.16). The OI/RA ratio was significantly higher for Bridging 3 than for Bridging 2. Based on these results, adding hip abduction and adduction, particularly bilateral movements, could be a useful method to enhance OI and MF EMG activity and their activities relative to global muscles during bridging exercise. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Bridging exercise Electromyography Hip movement Trunk muscles
1. Introduction Involvement of trunk muscles is essential to maintain stable movement patterns with appropriate sequence and motor control while performing a variety of day-to-day physical activities, thereby accomplishing optimal performance levels within an acceptable range of physical abilities (Hodges and Richardson, 1997a). Feed-forward postural activation of trunk muscles in response to predictable perturbations may be more pronounced when an additional load, with voluntary limb motion, is imposed (Hodges et al., 1999). Poor neuromuscular control in the trunk muscles is known to be associated with musculoskeletal discomfort in the lumbopelvic region during physical activity, lumbar instability, alteration in muscle activation pattern, and
* Corresponding author. Tel.: þ82 43 229 8679; fax: þ82 43 229 8969. E-mail address: [email protected] (D.-w. Oh).
delayed recruitment of trunk-supporting muscles (O’Sullivan et al., 1997; Hodges and Richardson, 1999; Richardson et al., 2004). The trunk musculature is divided into global and local muscle groups, which play an important role in optimizing trunk stability during a variety of daily activities (Kisner and Colby, 2007). The larger global muscles act as large guy wires that cross multiple segments, function to control spinal orientation, and play a role in stabilizing the entire spinal column, rather than individual spinal segments, in response to greater external forces imposed by altered body configurations and displacements of the center of gravity (Hodges and Richardson, 1997a; Hodges et al., 1999). The smaller, segmentally related local muscles, including the transverse abdominal, oblique internals, and multifidus, provide stabilization to motions of spinal segments, depending on the speed of the movement (Hodges and Richardson, 1997b, 1999). Hence, global and local muscles are not isolated in maintaining an appropriate pattern of trunk mobility and stability during daily activities, but work together in a complementary fashion to create the optimal
1356-689X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.11.002
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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H. Park et al. / Manual Therapy xxx (2013) 1e6
activity levels (Cholewicki and VanVliet, 2002; Kisner and Colby, 2007). Bridging exercise has been recognized clinically for enhancing neuromuscular control of trunk flexor and extensor muscles and strengthening pelvic and lower limb muscles, which may be beneficial for reinforcing the functional stability of the trunk and the lumbopelvic region (Kisner and Colby, 2007). Previous studies have frequently tested bridging exercise with simple modifications to augment efficacy and effectively activate trunk-stabilizing muscles, e.g., supine bridge lifting one leg with knee flexed or extended on stable or unstable surfaces (Kumar and Narayan, 2001; Stevens et al., 2006; García-Vaquero et al., 2012). Recent data support integrating upper and lower limb motions into bridging exercise to allow an increasing stabilization effort that coordinates trunk muscles in optimal patterns under loading via limbs in order to keep the neutral position of the spine (Kisner and Colby, 2007). In addition, recent research has introduced bridging exercise with positioning of the distal parts of lower limbs in a sling system to add a dynamic stabilization effort with easy application (Saliba et al., 2010). Research efforts exploring additional options to promote the efficacy of bridging exercise rather than focusing on the simple application of the exercise should continue. In general, bridging exercise has been accepted as a basic method to facilitate functional control of the trunk muscles in a clinical setting. During bridging exercise, dynamic stabilization exertion caused by concurrent limb movement leads to increased activation of sensory receptors and additional stimulation of internal and external articular structures, reinforcing the motion control of trunk muscles (Kisner and Colby, 2007; Page et al., 2010; Saliba et al., 2010). However, to our knowledge, the effect of integrating dynamic limb movement to enhance the influence of bridging exercise on the activation of trunk muscles has had little attention, and the evidence remains unclear. Accordingly, this study aimed to clarify whether incorporation of hip movements alters the electromyographic (EMG) activation of selected trunk muscles during bridging exercises in healthy young adults. 2. Methods 2.1. Subjects Twenty-six healthy adults (13 men and 13 women) volunteered for this study. Their age, weight, and height were 21.23 2.16 years, 59.58 9.59 kg, and 167.46 7.40 cm, respectively. Inclusion criteria were as follows: (1) no previous or current neurological and musculoskeletal illnesses that could influence on exercise performance; (2) no limitation in hip joint motion or significant weakness of lower limb muscles; (3) no history of surgery in the trunk and lumbopelvic region; and (4) no psychological problems. Pregnant women were excluded. Prior to the initiation of the study, the entire experimental process was described to the subjects, and each participant signed a written informed consent form. The protocol for this study was approved by Institutional Review Board of Daejeon University. 2.2. EMG recording and data processing EMG data were obtained simultaneously from selected trunk muscles (rectus abdominis [RA], obliquus internus [OI], erector spinae [ES], and multifidus [MF]) by using a 4-channel portable system featuring a signal conditioner (QEMG-4 System, LXM 3204; Laxtha, Daejeon, Korea). After skin preparation, disposable Ag/AgCl surface electrodes were attached over the muscles of the dominant side. Electrodes for the RA were placed proximally, 3 cm lateral to
the umbilicus (Cram et al., 1998; Stevens et al., 2006), and electrodes for the OI were positioned horizontally 2 cm inward and distal to the anterior superior iliac spine (ASIS) (Escamilla et al., 2010). Electrodes for the ES were attached proximally 3 cm lateral to the L3 spinous process (Cram et al., 1998; Escamilla et al., 2010), and electrodes for MF were positioned above and below and aligned transversely to both posterior superior iliac spines (Danneels et al., 2002; Stevens et al., 2006). A ground electrode was placed on the ASIS. The overall gain for EMG signals was 1785.7, and band-pass (20e450 Hz) and notch filters (50 Hz) were used. The raw EMG signals were sampled at 1000 Hz and processed to a root mean square (RMS) format using a moving window of 10 ms. The RMS value has frequently been chosen by clinicians to quantify EMG signals because it represents the level of motor unit activity during muscle contraction (Fukuda et al., 2008). To normalize EMG signals collected from each muscle, the RMS of 5-s maximal voluntary isometric contraction (MVIC) was obtained from each muscle at the positions of manual muscle testing suggested by Vizniak and Richer (2011). The EMG signals recorded from each muscle during bridging exercises were calculated as a percentage of the RMS of the MVIC (% MVIC). For further analysis, the IO/RA and MF/ES ratios were calculated to identify relative values of the activities of local muscle (IO and MF) to those of the activities of global muscles (RA and ES). All EMG data were averaged over triplicate trials with 3-min intervals. 2.3. Procedures All EMG recordings were carried out with the subject in a supine position on the table. The EMG data were recorded for RA, OI, ES, and MF during bridging exercises with the distal portions of both legs placed in the sling suspension system (Redcord Trainer AS, Norway). The bridging exercise was started from the supine position with palms facing down, and the ankle regions of both lower legs were placed with the feet at shoulder width in the holding straps of the sling suspension system to establish the body suspension point during the bridging exercise. The height of the straps was adjusted in accordance with the knee level in hooklying position with knee flexed to 90 . Bridging exercises were performed using an abdominal drawing-in maneuver that requires gently drawing the lower abdomen in after expiration (Teyhen et al., 2007). To perform the bridging exercise, the subjects were instructed to lift the pelvis until the angle of hip flexion reached 0 , and to hold this position during the EMG measurements. This study used three experimental options for bridging exercises to record the EMG activities of the selected trunk muscles. They were: (1) bridging exercise alone (Bridging 1), (2) incorporating unilateral hip abduction and adduction (20 ) of the nondominant leg (Bridging 2), and (3) incorporating bilateral hip abduction and adduction of both legs (20 to each side) (Bridging 3) (Fig. 1). The three types of exercise were performed in randomized order, which was determined by selecting a single card without looking from an envelope with three cards marked with 1, 2, or 3. To assure a range of 20 in hip abduction during bridging exercise, target bars were positioned at the lateral sides of both knee joints, and the subjects were asked to keep the lateral portion of the knee at the target bar. In addition, control bars with centimeter markings were placed at 3 cm intervals from the lateral sides of the pelvis to prevent unexpected trunk and pelvis motion in sagittal and transverse planes. The subjects were instructed to maintain the interval between the pelvis and the bar without touching the bars, and to keep the position of the anterior superior iliac spines within a ventral-to-dorsal movement range of 2 cm from the initial bridging position while performing the bridging exercises. EMG
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
H. Park et al. / Manual Therapy xxx (2013) 1e6
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Fig. 1. Experimental protocol for the bridging exercises. (A) Starting position. (B) Bridging 1: bridge exercise alone. (C) Bridging 2: incorporation of unilateral hip abduction and adduction movement (D) Bridging 3: incorporation of bilateral hips.
signals were collected for a bridging time of 8 s, which comprised the bridging hold for Bridging 1 and hip abduction and adduction (2 s for each movement) for Bridging 2 and 3, respectively, in the middle time interval of 4 s. Further analysis included EMG data obtained from the middle interval. Subjects were guided by a digital metronome (QEMG-4 System, LXM 3204; Laxtha, Daejeon, Korea) to maintain movement speed in a suitable time template, with a beeper sound to signal them to start hip abduction in the bridging position. For the EMG recordings, the completion of hip adduction was determined by contact with a foot switch that was attached to the medial side of right heel. EMG measurements were performed in one trial of hip abduction and adduction during bridging exercise. Prior to EMG measurements, the subjects practiced bridging exercises under these conditions for 10 min to enable them to perform the hip movements precisely. Fig. 1 shows the starting position of the bridging exercises and the three experimental conditions for this study. 2.4. Data analysis Statistical analysis for all results was performed using Statistical Package for the Social Sciences version 18.0 software (SPSS Inc., Chicago, IL, USA). All EMG data were expressed as means standard deviations. Repeated-measures analyses of variance (ANOVA) were
used to compare EMG data collected from each muscle (RA, OI, ES, and MF) and relative EMG activity ratios (IO/RA and MF/ES) among the three bridging conditions. When statistical significance for any data was found, post-hoc analysis for multiple pairwise comparisons was performed using the least significant difference method. The level of statistical significance was set at p < 0.05. 3. Results Table 1 describes the EMG data collected for ES, MF, RA, and OI while performing 3 types of bridging exercise, respectively. In Fig. 2, Table 1 EMG activity (%MVIC) of the selected trunk muscles during bridging exercises. Bridging 1 RA OI ES MF
6.19 6.14 40.04 39.08
Bridging 2 a
4.25 2.78 8.43 10.29
6.73 8.98 39.34 39.72
Bridging 3 b
4.32 3.87b 9.14 9.80
6.59 10.97 40.47 41.41
b
4.16 4.85b,c 8.14 10.50b,c
df
F
P
2 2 2 2
6.080 24.243 1.462 3.853
0.007 0.000 0.252 0.035
RA e rectus abdominis; OI e obliquus internus; ES e erector spine; MF e multifidus; Bridging 1 e bridging exercise alone; Bridging 2 e bridging exercise with unilateral hip movement; Bridging 3 e bridging exercise with bilateral hip movement. a Mean SD. b Significant difference in comparison with Bridging 1. c Significant difference in comparison with Bridging 2.
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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H. Park et al. / Manual Therapy xxx (2013) 1e6
Fig. 2. Raw EMG data are shown for a representative subject. RA: rectus abdominis; OI: obliquus internus; ES: erector spinae; MF: multifidus. Bridging 1: bridging exercise alone; Bridging 2: bridging exercise with unilateral hip movement; Bridging 3: bridging exercise with bilateral hip movement.
raw EMG data of each muscle are shown for a representative subject. Significant differences between bridging exercises were found for RA, OI, and MF (p < 0.05). In post-hoc pairwise analysis, RA and OI showed greater EMG activity during Bridging 2 (RA: p ¼ 0.002, and OI: p ¼ 0.000) and Bridging 3 (RA: p ¼ 0.016, and OI: p ¼ 0.000) compared to Bridging 1 and in the OI, the EMG activity in Bridging 3 was greater than that of Bridging 2 (p ¼ 0.012). The activity of the MF appeared to be greater for Bridging 3 than for Bridging 1 (p ¼ 0.016) and Bridging 2 (p ¼ 0.027). Table 2 summarizes relative EMG activity ratios of local trunk muscles to global muscles. The MF/ES and OI/RA ratios showed statistically significant differences (p < 0.05). In post-hoc analysis, the OI/RA and MF/ES ratios were significantly higher for Bridging 2 (OI/RA ratio: p ¼ 0.002, and MF/ES ratio: p ¼ 0.046) and Bridging 3 (OI/RA ratio: p ¼ 0.000, and MF/ES ratio: p ¼ 0.000) than for Bridging 1. The OI/RA ratio was significantly higher for Bridging 3 than for Bridging 2 (p ¼ 0.031).
4. Discussion The basic concept of this study was to explore the benefits of incorporating additional limb motion to reinforce the stabilization efforts of the trunk muscles during bridging exercise. Our results suggest that the activities of the OI and MF, which contribute to trunk stabilization during daily activities, may be more appropriately facilitated when integrating hip movement into bridging
Table 2 Relative EMG activity ratios of local trunk muscles to global muscles during bridging exercises.
OI/RA MF/ES
Bridging 1
Bridging 2
Bridging 3
df
F
P
1.35 0.92a 0.98 0.16
1.89 1.41b 1.03 0.19b
2.34 1.86b,c 1.03 0.15b
2 2
11.966 10.287
0.000 0.001
RA e rectus abdominis; OI e obliquus internus; ES e erector spine; MF e multifidus; Bridging 1 e bridging exercise alone; Bridging 2 e bridging exercise with unilateral hip movement; Bridging 3 e bridging exercise with bilateral hip movement. a Mean SD. b Significant difference in comparison with Bridging 1. c Significant difference in comparison with Bridging 2.
exercise, and this effect may be more favorable with incorporation of bilateral hip movements than with unilateral hip movement. Poor control of local muscles causes compressive loading on individual spinal segments induced from the action of larger global muscles, which is possible factor in the onset of musculoskeletal problems in the lumbopelvic regions (Kisner and Colby, 2007). In general, trunk stabilization may be due to the action of the local stabilizing muscles of the trunk, and these actions should be modified in relation to the recruitment of the larger global trunk muscles, depending on the level of activity (O’Sullivan et al., 1997; Marshall and Murphy, 2005; Stevens et al., 2006). Therefore, it is more important to identify the relative activity level of the local trunk-stabilizing muscles to that of the larger global muscles (Marshall and Murphy, 2005; Stevens et al., 2006). In the present study, this relationship was determined by measuring the EMG amplitudes of RA, OI, ES, and MF, adjusting trunk and pelvis movement in a stable pattern during static and dynamic activities (Stevens et al., 2006; Escamilla et al., 2010; García-Vaquero et al., 2012), and including analysis of IO/RA and MF/ES ratios to obtain additional information for the relative contribution of selected trunk muscles. According to the findings of another recent study that suggested that these muscles may be affected by loading induced from unilateral and bilateral limb movement (Tarnanen et al., 2008), we used the extra loading provided by integrating hip abduction and adduction motions in a range of 20 during bridging exercises, simulating the necessary range of hip abduction for carrying out normal activities of daily living (Kisner and Colby, 2007). During limb movement, these muscles are mainly responsible for maintaining trunk stability, which is a requirement for better performance. In particular, unilateral movements with a limb support lead to the increase of muscular effort on the supporting side to control against the force of gravity and provide momentum for balance and stability (Kisner and Colby, 2007). This finding supports our choice for EMG data collection on the contralateral side in Bridging 2 (bridging exercise plus unilateral hip movement). In this study, most muscles were activated more during the bridging exercises with either unilateral or bilateral hip movements than during bridging exercise alone, and the activation patterns were encouraged more by bilateral hip movements. Furthermore, we found that the IO/RA and MF/ES ratios were further increased when bridging exercise was performed with hip movements. During bridging exercise, loading resistance induced from limb movement requires an additional stabilization effort to keep the lumbopelvic stability at an optimal level, which leads to increased stabilizing force in the abdominal region (Stevens et al., 2006; Kisner and Colby, 2007; Tarnanen et al., 2008; Saliba et al., 2010; García-Vaquero et al., 2012). Hip abduction and adduction movements during bridging exercise contribute to a transmission of forces to the local muscles of the abdominal region because the hip abductors are linked with the local muscles through the anterior superior iliac spine portion of the pelvis (Myers et al., 2001). Consequently, the contraction of the limb-girdle musculature may influence the activation of trunk-stabilizing muscles (Lee, 2004; Tarnanen et al., 2008; Page et al., 2010). A minimal activation of larger global muscles in relation to the local muscles has been considered a contributing factor for maintaining optimal trunk stabilization during a variety of physical activities (Stevens et al., 2006). Therefore, our results suggest that incorporating hip movements may be beneficial for enhancing the contribution of local muscles to trunk stabilization during bridging exercises. Our findings also support previous studies that have indicated that limb movements are beneficial for reinforcing the activity of the local trunk-stabilizing muscles during bridging exercise (Saliba et al., 2010).
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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In this study, although the differences in the MF/ES ratios among the bridging exercises had statistical significance, the changes were actually very small, and it is probably difficult to pinpoint the clinical benefits in improving the relative involvement of local muscle. Generally, the ES and MF have a tendency to control spinal stability in the same pattern while maintaining static or dynamic body conditions, regardless of the type of exercise and activity, and by doing so, they seem to work together to develop trunk stability during these kinds of activities (McGill et al., 2003). However, significant differences in the activity of the OI indicates that bridging exercises with hip movement, particularly bilateral movement, have clinical advantages in enhancing the control mechanism of trunk-stabilizing muscles, because the activity of the OI represents the activity of the transversus abdominis, which has a major part in stabilizing the trunk during a variety of activities (Juker et al., 1998). The close connection between the local abdominal muscles and the thoracolumbar fascia may have a positive effect in increasing lumbopelvic stabilization (Cresswell et al., 1992; McGill, 2002; Kisner and Colby, 2007). Therefore, the adaptive response of local muscle in abdominal region leads to the establishment of greater stability in the spinal segments by increasing thoracolumbar tension and sequentially developing intra-abdominal pressure (Cresswell et al., 1992). Although our study focused on the role of local muscles in trunk stabilization, clinical knowledge has recognized the importance of co-activation of local and global muscular systems for maintaining spinal stability (Kavcic et al., 2004). In fact, both muscle systems are not clearly distinct in their contribution to spinal stability (Cholewicki and VanVilet, 2002; Kavcic et al., 2004; Stevens et al., 2006). Therefore, clinicians should keep in mind that a coordinated control of local and global muscles is essential to provide a framework for spine stability, depending on various loading conditions occurring during daily activities. The general concept that has been suggested is that dynamic limb movements require the anticipatory control of trunkstabilizing muscles in an appropriate sequence with suitable force production by contractions to support load resistance and maintain stability, thus achieving the highest level of stable performance (Hodges and Richardson, 1997a; Hodges et al., 1999). Our study showed that bilateral hip movement might be more advantageous for reinforcing the trunk stabilizing effort during bridging exercise than unilateral movement. In unilateral hip movement, the involvement of trunk muscles in achieving an appropriate level of trunk stabilization may be established in relation to the supporting force of the fixed leg, whereas trunk stabilization during bilateral hip movement depends on the contribution of trunk muscles because of the change of the holding points of the legs to the starting points for limb movements. In addition, while performing bilateral hip movement, the legs form a larger movement arc compared to unilateral hip movement and the hip muscles can produce sufficient torque to cause a greater loading of the trunk muscles (Kisner and Colby, 2007). Therefore, it can be assumed that limb movements during bridging exercise, especially bilateral movements, can be used to elicit a sufficient level of contraction of the trunk muscles within a tolerable range for developing endurance and strength in advanced phases of rehabilitation for patients presenting low back pain or spinal instability, and for preventing low back injury. Another possible benefit may be the increased stimulation of the proprioceptive system during dynamic limb movements, leading to activation of the motor control system and reinforcing the coactivation of the trunk muscles. The proprioceptive system is responsible for detecting changes in joint position and motion of the trunk and limbs, modifying muscle length and tension by the action of various receptors, such as muscle spindles and Golgi tendon organs (Lephart et al., 1997). Integration of hip movements
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may make bridging exercise more challenging because it requires controlling the errors of active repositioning against the destabilizing torque and perturbation force of the trunk during the hip movements (Kisner and Colby, 2007; Page et al., 2010; Saliba et al., 2010; García-Vaquero et al., 2012). MF has generally been recognized as rich in proprioceptive receptors, and for this reason the role of MF may be to detect alterations in the position and movement of the trunk and to control the fine movement of trunk, as well as to create trunk movement (Solomonow et al., 1998; Ricardson et al., 2004). Dynamic hip movements can provide a better opportunity to facilitate sensory-motor feedback, which results in the recruitment of MF during the bridging exercise to establish efficient motor control strategies (Solomonow et al., 1998; Ricardson et al., 2004; Page et al., 2010), and this may be stimulated to greater extent with bilateral hip movements. For these reasons, combinations of bilateral limb movements have been commonly used as a beneficial method to improve the effects of trunk stabilization exercises for individuals in advanced stages of physical ability (Kisner and Colby, 2007). Our study has several limitations that can be addressed in future studies. First, this study included a relatively small group of healthy young people. Therefore, our results may be difficult to generalize to other populations with lumbopelvic disabilities such as low back pain and sacroiliac joint dysfunction. Second, we used surface EMG equipment to measure the activities of selected trunk muscles. When EMG data were collected from the selected muscles, crosstalk from adjacent muscles may have been a confounding factor that made the EMG values less reliable. Finally, in this study, the EMG activities of the muscles were measured while incorporating hip movement into bridging exercise. Although our methods included specific efforts to encourage participants to maintain the bridging position and the pace of hip abduction and adduction appropriately, it may be difficult to ensure that there was not an alteration in the position of trunk and pelvis that could influence the activities of the muscles during the exercises, because we did not use any qualitative equipment to control position and movement pace. Therefore, a more robust and large-scale clinical study is warranted. 5. Conclusion In general, bridging exercise has been considered favorably as a therapeutic strategy to develop optimal control of the lumbopelvic muscles and to promote trunk stabilization in clinical settings. Limb motion often requires the activities of local trunk-stabilizing muscles in coordination with the activities of larger global trunk muscles in the early phase to accept the changing load coming from the movements. Therefore, the integration of limb movement during bridging exercise may be a challenging option that offers an additional opportunity to promote the stabilization effort of trunk muscles by encouraging extra loading induced from the limb movement. Our study suggests that incorporating hip movement into bridging exercise may be more beneficial for facilitating the activity of the local trunk muscles such as OI and MF and for optimizing the activities of global and local trunk muscles than bridging exercise alone, with greater benefit from bilateral hip movement than from unilateral movement. Given that these exercises are clinically feasible, easily applied, and relatively efficacious; we propose that they may also be a better choice for clinicians who are attempting to develop the best therapeutic strategies for optimizing the stabilization control of the lumbopelvic muscles. References Cholewicki J, VanVliet JJ. Relative contribution of trunk muscles to the stability of the lumbar spine during isometric exertions. Clin Biomech 2002;17(2):99e105.
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Original article
Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals Hyun-ju Park a, Duck-won Oh b, *, Suhn-yeop Kim c a
Department of Physical Therapy, The Graduate School, Daejeon University, 96-3, Yongun-dong, Dong-gu, Daejeon, 300-716, Republic of Korea Department of Physical Therapy, College of Health Science, Cheongju University, 298 Daeseongro, Sangdang-gu, Cheongju, Chungbuk, 360-764, Republic of Korea c Department of Physical Therapy, College of Natural Science, Daejeon University, 96-3, Yongun-dong, Dong-gu, Daejeon, 300-716, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 February 2013 Received in revised form 24 October 2013 Accepted 1 November 2013
This study aimed to identify the electromyographic (EMG) effects in selected trunk muscles after incorporating hip movement into bridging exercise. Twenty-six healthy adults (13 men and 13 women) volunteered for this experiment. EMG data (% maximum voluntary isometric contraction) were recorded from the rectus abdominis (RA), obliquus internus (OI), erector spinae (ES), and multifidus (MF) muscles of the dominant side while the subjects performed 3 types of bridging exercise, including bridging alone (Bridging 1), bridging with unilateral hip movements (Bridging 2), and bridging with bilateral hip movements (Bridging 3) in a sling suspension system. The RA and OI showed greater EMG activity during Bridging 2 and 3 compared to Bridging 1, with the greatest OI activity during Bridging 3 (p < 0.05), and the activity of the MF appeared to be greater during Bridging 3 than during Bridging 1 and 2 (p < 0.05). Furthermore, the OI/RA and MF/ES ratios were significantly higher for Bridging 2 (OI/RA ¼ 1.89 1.41; MF/ES ¼ 1.03 0.19) and Bridging 3 (OI/RA ¼ 2.34 1.86; MF/ES ¼ 1.03 0.15) than Bridging 1 (IO/ RA ¼ 1.35 0.92; MF/ES ¼ 0.98 0.16). The OI/RA ratio was significantly higher for Bridging 3 than for Bridging 2. Based on these results, adding hip abduction and adduction, particularly bilateral movements, could be a useful method to enhance OI and MF EMG activity and their activities relative to global muscles during bridging exercise. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Bridging exercise Electromyography Hip movement Trunk muscles
1. Introduction Involvement of trunk muscles is essential to maintain stable movement patterns with appropriate sequence and motor control while performing a variety of day-to-day physical activities, thereby accomplishing optimal performance levels within an acceptable range of physical abilities (Hodges and Richardson, 1997a). Feed-forward postural activation of trunk muscles in response to predictable perturbations may be more pronounced when an additional load, with voluntary limb motion, is imposed (Hodges et al., 1999). Poor neuromuscular control in the trunk muscles is known to be associated with musculoskeletal discomfort in the lumbopelvic region during physical activity, lumbar instability, alteration in muscle activation pattern, and
* Corresponding author. Tel.: þ82 43 229 8679; fax: þ82 43 229 8969. E-mail address: [email protected] (D.-w. Oh).
delayed recruitment of trunk-supporting muscles (O’Sullivan et al., 1997; Hodges and Richardson, 1999; Richardson et al., 2004). The trunk musculature is divided into global and local muscle groups, which play an important role in optimizing trunk stability during a variety of daily activities (Kisner and Colby, 2007). The larger global muscles act as large guy wires that cross multiple segments, function to control spinal orientation, and play a role in stabilizing the entire spinal column, rather than individual spinal segments, in response to greater external forces imposed by altered body configurations and displacements of the center of gravity (Hodges and Richardson, 1997a; Hodges et al., 1999). The smaller, segmentally related local muscles, including the transverse abdominal, oblique internals, and multifidus, provide stabilization to motions of spinal segments, depending on the speed of the movement (Hodges and Richardson, 1997b, 1999). Hence, global and local muscles are not isolated in maintaining an appropriate pattern of trunk mobility and stability during daily activities, but work together in a complementary fashion to create the optimal
1356-689X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.11.002
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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H. Park et al. / Manual Therapy xxx (2013) 1e6
activity levels (Cholewicki and VanVliet, 2002; Kisner and Colby, 2007). Bridging exercise has been recognized clinically for enhancing neuromuscular control of trunk flexor and extensor muscles and strengthening pelvic and lower limb muscles, which may be beneficial for reinforcing the functional stability of the trunk and the lumbopelvic region (Kisner and Colby, 2007). Previous studies have frequently tested bridging exercise with simple modifications to augment efficacy and effectively activate trunk-stabilizing muscles, e.g., supine bridge lifting one leg with knee flexed or extended on stable or unstable surfaces (Kumar and Narayan, 2001; Stevens et al., 2006; García-Vaquero et al., 2012). Recent data support integrating upper and lower limb motions into bridging exercise to allow an increasing stabilization effort that coordinates trunk muscles in optimal patterns under loading via limbs in order to keep the neutral position of the spine (Kisner and Colby, 2007). In addition, recent research has introduced bridging exercise with positioning of the distal parts of lower limbs in a sling system to add a dynamic stabilization effort with easy application (Saliba et al., 2010). Research efforts exploring additional options to promote the efficacy of bridging exercise rather than focusing on the simple application of the exercise should continue. In general, bridging exercise has been accepted as a basic method to facilitate functional control of the trunk muscles in a clinical setting. During bridging exercise, dynamic stabilization exertion caused by concurrent limb movement leads to increased activation of sensory receptors and additional stimulation of internal and external articular structures, reinforcing the motion control of trunk muscles (Kisner and Colby, 2007; Page et al., 2010; Saliba et al., 2010). However, to our knowledge, the effect of integrating dynamic limb movement to enhance the influence of bridging exercise on the activation of trunk muscles has had little attention, and the evidence remains unclear. Accordingly, this study aimed to clarify whether incorporation of hip movements alters the electromyographic (EMG) activation of selected trunk muscles during bridging exercises in healthy young adults. 2. Methods 2.1. Subjects Twenty-six healthy adults (13 men and 13 women) volunteered for this study. Their age, weight, and height were 21.23 2.16 years, 59.58 9.59 kg, and 167.46 7.40 cm, respectively. Inclusion criteria were as follows: (1) no previous or current neurological and musculoskeletal illnesses that could influence on exercise performance; (2) no limitation in hip joint motion or significant weakness of lower limb muscles; (3) no history of surgery in the trunk and lumbopelvic region; and (4) no psychological problems. Pregnant women were excluded. Prior to the initiation of the study, the entire experimental process was described to the subjects, and each participant signed a written informed consent form. The protocol for this study was approved by Institutional Review Board of Daejeon University. 2.2. EMG recording and data processing EMG data were obtained simultaneously from selected trunk muscles (rectus abdominis [RA], obliquus internus [OI], erector spinae [ES], and multifidus [MF]) by using a 4-channel portable system featuring a signal conditioner (QEMG-4 System, LXM 3204; Laxtha, Daejeon, Korea). After skin preparation, disposable Ag/AgCl surface electrodes were attached over the muscles of the dominant side. Electrodes for the RA were placed proximally, 3 cm lateral to
the umbilicus (Cram et al., 1998; Stevens et al., 2006), and electrodes for the OI were positioned horizontally 2 cm inward and distal to the anterior superior iliac spine (ASIS) (Escamilla et al., 2010). Electrodes for the ES were attached proximally 3 cm lateral to the L3 spinous process (Cram et al., 1998; Escamilla et al., 2010), and electrodes for MF were positioned above and below and aligned transversely to both posterior superior iliac spines (Danneels et al., 2002; Stevens et al., 2006). A ground electrode was placed on the ASIS. The overall gain for EMG signals was 1785.7, and band-pass (20e450 Hz) and notch filters (50 Hz) were used. The raw EMG signals were sampled at 1000 Hz and processed to a root mean square (RMS) format using a moving window of 10 ms. The RMS value has frequently been chosen by clinicians to quantify EMG signals because it represents the level of motor unit activity during muscle contraction (Fukuda et al., 2008). To normalize EMG signals collected from each muscle, the RMS of 5-s maximal voluntary isometric contraction (MVIC) was obtained from each muscle at the positions of manual muscle testing suggested by Vizniak and Richer (2011). The EMG signals recorded from each muscle during bridging exercises were calculated as a percentage of the RMS of the MVIC (% MVIC). For further analysis, the IO/RA and MF/ES ratios were calculated to identify relative values of the activities of local muscle (IO and MF) to those of the activities of global muscles (RA and ES). All EMG data were averaged over triplicate trials with 3-min intervals. 2.3. Procedures All EMG recordings were carried out with the subject in a supine position on the table. The EMG data were recorded for RA, OI, ES, and MF during bridging exercises with the distal portions of both legs placed in the sling suspension system (Redcord Trainer AS, Norway). The bridging exercise was started from the supine position with palms facing down, and the ankle regions of both lower legs were placed with the feet at shoulder width in the holding straps of the sling suspension system to establish the body suspension point during the bridging exercise. The height of the straps was adjusted in accordance with the knee level in hooklying position with knee flexed to 90 . Bridging exercises were performed using an abdominal drawing-in maneuver that requires gently drawing the lower abdomen in after expiration (Teyhen et al., 2007). To perform the bridging exercise, the subjects were instructed to lift the pelvis until the angle of hip flexion reached 0 , and to hold this position during the EMG measurements. This study used three experimental options for bridging exercises to record the EMG activities of the selected trunk muscles. They were: (1) bridging exercise alone (Bridging 1), (2) incorporating unilateral hip abduction and adduction (20 ) of the nondominant leg (Bridging 2), and (3) incorporating bilateral hip abduction and adduction of both legs (20 to each side) (Bridging 3) (Fig. 1). The three types of exercise were performed in randomized order, which was determined by selecting a single card without looking from an envelope with three cards marked with 1, 2, or 3. To assure a range of 20 in hip abduction during bridging exercise, target bars were positioned at the lateral sides of both knee joints, and the subjects were asked to keep the lateral portion of the knee at the target bar. In addition, control bars with centimeter markings were placed at 3 cm intervals from the lateral sides of the pelvis to prevent unexpected trunk and pelvis motion in sagittal and transverse planes. The subjects were instructed to maintain the interval between the pelvis and the bar without touching the bars, and to keep the position of the anterior superior iliac spines within a ventral-to-dorsal movement range of 2 cm from the initial bridging position while performing the bridging exercises. EMG
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H. Park et al. / Manual Therapy xxx (2013) 1e6
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Fig. 1. Experimental protocol for the bridging exercises. (A) Starting position. (B) Bridging 1: bridge exercise alone. (C) Bridging 2: incorporation of unilateral hip abduction and adduction movement (D) Bridging 3: incorporation of bilateral hips.
signals were collected for a bridging time of 8 s, which comprised the bridging hold for Bridging 1 and hip abduction and adduction (2 s for each movement) for Bridging 2 and 3, respectively, in the middle time interval of 4 s. Further analysis included EMG data obtained from the middle interval. Subjects were guided by a digital metronome (QEMG-4 System, LXM 3204; Laxtha, Daejeon, Korea) to maintain movement speed in a suitable time template, with a beeper sound to signal them to start hip abduction in the bridging position. For the EMG recordings, the completion of hip adduction was determined by contact with a foot switch that was attached to the medial side of right heel. EMG measurements were performed in one trial of hip abduction and adduction during bridging exercise. Prior to EMG measurements, the subjects practiced bridging exercises under these conditions for 10 min to enable them to perform the hip movements precisely. Fig. 1 shows the starting position of the bridging exercises and the three experimental conditions for this study. 2.4. Data analysis Statistical analysis for all results was performed using Statistical Package for the Social Sciences version 18.0 software (SPSS Inc., Chicago, IL, USA). All EMG data were expressed as means standard deviations. Repeated-measures analyses of variance (ANOVA) were
used to compare EMG data collected from each muscle (RA, OI, ES, and MF) and relative EMG activity ratios (IO/RA and MF/ES) among the three bridging conditions. When statistical significance for any data was found, post-hoc analysis for multiple pairwise comparisons was performed using the least significant difference method. The level of statistical significance was set at p < 0.05. 3. Results Table 1 describes the EMG data collected for ES, MF, RA, and OI while performing 3 types of bridging exercise, respectively. In Fig. 2, Table 1 EMG activity (%MVIC) of the selected trunk muscles during bridging exercises. Bridging 1 RA OI ES MF
6.19 6.14 40.04 39.08
Bridging 2 a
4.25 2.78 8.43 10.29
6.73 8.98 39.34 39.72
Bridging 3 b
4.32 3.87b 9.14 9.80
6.59 10.97 40.47 41.41
b
4.16 4.85b,c 8.14 10.50b,c
df
F
P
2 2 2 2
6.080 24.243 1.462 3.853
0.007 0.000 0.252 0.035
RA e rectus abdominis; OI e obliquus internus; ES e erector spine; MF e multifidus; Bridging 1 e bridging exercise alone; Bridging 2 e bridging exercise with unilateral hip movement; Bridging 3 e bridging exercise with bilateral hip movement. a Mean SD. b Significant difference in comparison with Bridging 1. c Significant difference in comparison with Bridging 2.
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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H. Park et al. / Manual Therapy xxx (2013) 1e6
Fig. 2. Raw EMG data are shown for a representative subject. RA: rectus abdominis; OI: obliquus internus; ES: erector spinae; MF: multifidus. Bridging 1: bridging exercise alone; Bridging 2: bridging exercise with unilateral hip movement; Bridging 3: bridging exercise with bilateral hip movement.
raw EMG data of each muscle are shown for a representative subject. Significant differences between bridging exercises were found for RA, OI, and MF (p < 0.05). In post-hoc pairwise analysis, RA and OI showed greater EMG activity during Bridging 2 (RA: p ¼ 0.002, and OI: p ¼ 0.000) and Bridging 3 (RA: p ¼ 0.016, and OI: p ¼ 0.000) compared to Bridging 1 and in the OI, the EMG activity in Bridging 3 was greater than that of Bridging 2 (p ¼ 0.012). The activity of the MF appeared to be greater for Bridging 3 than for Bridging 1 (p ¼ 0.016) and Bridging 2 (p ¼ 0.027). Table 2 summarizes relative EMG activity ratios of local trunk muscles to global muscles. The MF/ES and OI/RA ratios showed statistically significant differences (p < 0.05). In post-hoc analysis, the OI/RA and MF/ES ratios were significantly higher for Bridging 2 (OI/RA ratio: p ¼ 0.002, and MF/ES ratio: p ¼ 0.046) and Bridging 3 (OI/RA ratio: p ¼ 0.000, and MF/ES ratio: p ¼ 0.000) than for Bridging 1. The OI/RA ratio was significantly higher for Bridging 3 than for Bridging 2 (p ¼ 0.031).
4. Discussion The basic concept of this study was to explore the benefits of incorporating additional limb motion to reinforce the stabilization efforts of the trunk muscles during bridging exercise. Our results suggest that the activities of the OI and MF, which contribute to trunk stabilization during daily activities, may be more appropriately facilitated when integrating hip movement into bridging
Table 2 Relative EMG activity ratios of local trunk muscles to global muscles during bridging exercises.
OI/RA MF/ES
Bridging 1
Bridging 2
Bridging 3
df
F
P
1.35 0.92a 0.98 0.16
1.89 1.41b 1.03 0.19b
2.34 1.86b,c 1.03 0.15b
2 2
11.966 10.287
0.000 0.001
RA e rectus abdominis; OI e obliquus internus; ES e erector spine; MF e multifidus; Bridging 1 e bridging exercise alone; Bridging 2 e bridging exercise with unilateral hip movement; Bridging 3 e bridging exercise with bilateral hip movement. a Mean SD. b Significant difference in comparison with Bridging 1. c Significant difference in comparison with Bridging 2.
exercise, and this effect may be more favorable with incorporation of bilateral hip movements than with unilateral hip movement. Poor control of local muscles causes compressive loading on individual spinal segments induced from the action of larger global muscles, which is possible factor in the onset of musculoskeletal problems in the lumbopelvic regions (Kisner and Colby, 2007). In general, trunk stabilization may be due to the action of the local stabilizing muscles of the trunk, and these actions should be modified in relation to the recruitment of the larger global trunk muscles, depending on the level of activity (O’Sullivan et al., 1997; Marshall and Murphy, 2005; Stevens et al., 2006). Therefore, it is more important to identify the relative activity level of the local trunk-stabilizing muscles to that of the larger global muscles (Marshall and Murphy, 2005; Stevens et al., 2006). In the present study, this relationship was determined by measuring the EMG amplitudes of RA, OI, ES, and MF, adjusting trunk and pelvis movement in a stable pattern during static and dynamic activities (Stevens et al., 2006; Escamilla et al., 2010; García-Vaquero et al., 2012), and including analysis of IO/RA and MF/ES ratios to obtain additional information for the relative contribution of selected trunk muscles. According to the findings of another recent study that suggested that these muscles may be affected by loading induced from unilateral and bilateral limb movement (Tarnanen et al., 2008), we used the extra loading provided by integrating hip abduction and adduction motions in a range of 20 during bridging exercises, simulating the necessary range of hip abduction for carrying out normal activities of daily living (Kisner and Colby, 2007). During limb movement, these muscles are mainly responsible for maintaining trunk stability, which is a requirement for better performance. In particular, unilateral movements with a limb support lead to the increase of muscular effort on the supporting side to control against the force of gravity and provide momentum for balance and stability (Kisner and Colby, 2007). This finding supports our choice for EMG data collection on the contralateral side in Bridging 2 (bridging exercise plus unilateral hip movement). In this study, most muscles were activated more during the bridging exercises with either unilateral or bilateral hip movements than during bridging exercise alone, and the activation patterns were encouraged more by bilateral hip movements. Furthermore, we found that the IO/RA and MF/ES ratios were further increased when bridging exercise was performed with hip movements. During bridging exercise, loading resistance induced from limb movement requires an additional stabilization effort to keep the lumbopelvic stability at an optimal level, which leads to increased stabilizing force in the abdominal region (Stevens et al., 2006; Kisner and Colby, 2007; Tarnanen et al., 2008; Saliba et al., 2010; García-Vaquero et al., 2012). Hip abduction and adduction movements during bridging exercise contribute to a transmission of forces to the local muscles of the abdominal region because the hip abductors are linked with the local muscles through the anterior superior iliac spine portion of the pelvis (Myers et al., 2001). Consequently, the contraction of the limb-girdle musculature may influence the activation of trunk-stabilizing muscles (Lee, 2004; Tarnanen et al., 2008; Page et al., 2010). A minimal activation of larger global muscles in relation to the local muscles has been considered a contributing factor for maintaining optimal trunk stabilization during a variety of physical activities (Stevens et al., 2006). Therefore, our results suggest that incorporating hip movements may be beneficial for enhancing the contribution of local muscles to trunk stabilization during bridging exercises. Our findings also support previous studies that have indicated that limb movements are beneficial for reinforcing the activity of the local trunk-stabilizing muscles during bridging exercise (Saliba et al., 2010).
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
H. Park et al. / Manual Therapy xxx (2013) 1e6
In this study, although the differences in the MF/ES ratios among the bridging exercises had statistical significance, the changes were actually very small, and it is probably difficult to pinpoint the clinical benefits in improving the relative involvement of local muscle. Generally, the ES and MF have a tendency to control spinal stability in the same pattern while maintaining static or dynamic body conditions, regardless of the type of exercise and activity, and by doing so, they seem to work together to develop trunk stability during these kinds of activities (McGill et al., 2003). However, significant differences in the activity of the OI indicates that bridging exercises with hip movement, particularly bilateral movement, have clinical advantages in enhancing the control mechanism of trunk-stabilizing muscles, because the activity of the OI represents the activity of the transversus abdominis, which has a major part in stabilizing the trunk during a variety of activities (Juker et al., 1998). The close connection between the local abdominal muscles and the thoracolumbar fascia may have a positive effect in increasing lumbopelvic stabilization (Cresswell et al., 1992; McGill, 2002; Kisner and Colby, 2007). Therefore, the adaptive response of local muscle in abdominal region leads to the establishment of greater stability in the spinal segments by increasing thoracolumbar tension and sequentially developing intra-abdominal pressure (Cresswell et al., 1992). Although our study focused on the role of local muscles in trunk stabilization, clinical knowledge has recognized the importance of co-activation of local and global muscular systems for maintaining spinal stability (Kavcic et al., 2004). In fact, both muscle systems are not clearly distinct in their contribution to spinal stability (Cholewicki and VanVilet, 2002; Kavcic et al., 2004; Stevens et al., 2006). Therefore, clinicians should keep in mind that a coordinated control of local and global muscles is essential to provide a framework for spine stability, depending on various loading conditions occurring during daily activities. The general concept that has been suggested is that dynamic limb movements require the anticipatory control of trunkstabilizing muscles in an appropriate sequence with suitable force production by contractions to support load resistance and maintain stability, thus achieving the highest level of stable performance (Hodges and Richardson, 1997a; Hodges et al., 1999). Our study showed that bilateral hip movement might be more advantageous for reinforcing the trunk stabilizing effort during bridging exercise than unilateral movement. In unilateral hip movement, the involvement of trunk muscles in achieving an appropriate level of trunk stabilization may be established in relation to the supporting force of the fixed leg, whereas trunk stabilization during bilateral hip movement depends on the contribution of trunk muscles because of the change of the holding points of the legs to the starting points for limb movements. In addition, while performing bilateral hip movement, the legs form a larger movement arc compared to unilateral hip movement and the hip muscles can produce sufficient torque to cause a greater loading of the trunk muscles (Kisner and Colby, 2007). Therefore, it can be assumed that limb movements during bridging exercise, especially bilateral movements, can be used to elicit a sufficient level of contraction of the trunk muscles within a tolerable range for developing endurance and strength in advanced phases of rehabilitation for patients presenting low back pain or spinal instability, and for preventing low back injury. Another possible benefit may be the increased stimulation of the proprioceptive system during dynamic limb movements, leading to activation of the motor control system and reinforcing the coactivation of the trunk muscles. The proprioceptive system is responsible for detecting changes in joint position and motion of the trunk and limbs, modifying muscle length and tension by the action of various receptors, such as muscle spindles and Golgi tendon organs (Lephart et al., 1997). Integration of hip movements
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may make bridging exercise more challenging because it requires controlling the errors of active repositioning against the destabilizing torque and perturbation force of the trunk during the hip movements (Kisner and Colby, 2007; Page et al., 2010; Saliba et al., 2010; García-Vaquero et al., 2012). MF has generally been recognized as rich in proprioceptive receptors, and for this reason the role of MF may be to detect alterations in the position and movement of the trunk and to control the fine movement of trunk, as well as to create trunk movement (Solomonow et al., 1998; Ricardson et al., 2004). Dynamic hip movements can provide a better opportunity to facilitate sensory-motor feedback, which results in the recruitment of MF during the bridging exercise to establish efficient motor control strategies (Solomonow et al., 1998; Ricardson et al., 2004; Page et al., 2010), and this may be stimulated to greater extent with bilateral hip movements. For these reasons, combinations of bilateral limb movements have been commonly used as a beneficial method to improve the effects of trunk stabilization exercises for individuals in advanced stages of physical ability (Kisner and Colby, 2007). Our study has several limitations that can be addressed in future studies. First, this study included a relatively small group of healthy young people. Therefore, our results may be difficult to generalize to other populations with lumbopelvic disabilities such as low back pain and sacroiliac joint dysfunction. Second, we used surface EMG equipment to measure the activities of selected trunk muscles. When EMG data were collected from the selected muscles, crosstalk from adjacent muscles may have been a confounding factor that made the EMG values less reliable. Finally, in this study, the EMG activities of the muscles were measured while incorporating hip movement into bridging exercise. Although our methods included specific efforts to encourage participants to maintain the bridging position and the pace of hip abduction and adduction appropriately, it may be difficult to ensure that there was not an alteration in the position of trunk and pelvis that could influence the activities of the muscles during the exercises, because we did not use any qualitative equipment to control position and movement pace. Therefore, a more robust and large-scale clinical study is warranted. 5. Conclusion In general, bridging exercise has been considered favorably as a therapeutic strategy to develop optimal control of the lumbopelvic muscles and to promote trunk stabilization in clinical settings. Limb motion often requires the activities of local trunk-stabilizing muscles in coordination with the activities of larger global trunk muscles in the early phase to accept the changing load coming from the movements. Therefore, the integration of limb movement during bridging exercise may be a challenging option that offers an additional opportunity to promote the stabilization effort of trunk muscles by encouraging extra loading induced from the limb movement. Our study suggests that incorporating hip movement into bridging exercise may be more beneficial for facilitating the activity of the local trunk muscles such as OI and MF and for optimizing the activities of global and local trunk muscles than bridging exercise alone, with greater benefit from bilateral hip movement than from unilateral movement. Given that these exercises are clinically feasible, easily applied, and relatively efficacious; we propose that they may also be a better choice for clinicians who are attempting to develop the best therapeutic strategies for optimizing the stabilization control of the lumbopelvic muscles. References Cholewicki J, VanVliet JJ. Relative contribution of trunk muscles to the stability of the lumbar spine during isometric exertions. Clin Biomech 2002;17(2):99e105.
Please cite this article in press as: Park H-j, et al., Effects of integrating hip movements into bridge exercises on electromyographic activities of selected trunk muscles in healthy individuals, Manual Therapy (2013), http://dx.doi.org/10.1016/j.math.2013.11.002
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