Abstract
[Purpose] This study investigated the effect of psoas major pre-activation on the electromyographic (EMG) activity of the abdominal muscles and pelvic rotation during active leg raising (ALR). [Participants and Methods] Twenty healthy participants were enrolled. ALR was performed in a conventional manor or with contralateral psoas major (cPM) pre-activation. The EMG activity of the abdominal muscles, including the rectus abdominalis (RA), external oblique (EO), and internal oblique (IO), was measured, as was pelvic rotation. Paired t-tests were used. [Results] The EMG activity of all studied muscles was significantly increased, and pelvic rotation was significantly decreased, during ALR with psoas major pre-activation compared to the levels under conventional testing. [Conclusion] cPM pre-activation during ALR can increase abdominal muscle activity and minimize pelvic rotation.
Key words: Active leg raising, Pre-activation, Psoas major
INTRODUCTION
The psoas major muscle (PM) is considered as a stabilizer for the lumbar spine1). During active leg raising (ALR), the iliacus, rectus femoris, and ipsilateral PM (iPM) are activated, as is the contralateral PM (cPM)1). Furthermore, the thickness of the cPM is significantly greater during ALR2). These findings suggest that the cPM could be activated to stabilize the lumbar spine during ALR1, 2). PM muscle activation can increase with greater hip flexion. However, the PM mainly works as a stabilizer of the lumbar spine through the first 15° of hip flexion3). Although the stabilizing function of the PM may be an important factor in rehabilitation of the spine, few reports have investigated interventions for cPM pre-activation as a means of minimizing pelvic compensation during ALR. The purpose of this study was to investigate the effect of cPM pre-activation on the electromyographic (EMG) activity of the abdominal muscles, and on pelvic rotation during ALR in healthy participants.
PARTICIPANTS AND METHODS
Twenty healthy males aged 20–28 years (mean age: 22.3 ± 5.19 years; mean height: 174.3 ± 4.85 cm; mean weight: 70.4 ± 11.15 kg) participated in this study. The experimental protocols and methods were explained in detail to all individuals, and all participants provided written informed consent in keeping with the ethical principles of the Declaration of Helsinki. EMG feedback was conveyed by a wireless telemetry system (Wireless EMG System (1000RT), BTS, Millan, Italy). To analyze abdominal muscle contraction, we used surface EMG with the bundled analysis software. A digital band-pass filter (Lancosh FIR) filtered movement artifacts at 20–450 Hz, and the sample rate was set to 1,024 Hz. The EMG signals were processed via root mean square with a moving window of 50 ms.
The electrodes for the IO, EO, and RA were placed according to Criswell4). The electrodes for PM was placed 2 cm lateral to the femoral artery and 1 cm below the inguinal ligament. All EMG signals are expressed as percentages of the maximum voluntary contraction (%MVIC). The Polhemus Liberty™ tracking system (Polhemus, Colchester, VT, USA) was used to investigate pelvic rotation at 120 Hz, and to monitor compensatory rotation during the exercises. Electromagnetic motion sensors were attached to the skin at the bilateral ASIS to measure pelvic rotation during exercises. All exercises were performed in a supine position, and measurements were recorded with conventional ALR or ALR with cPM pre-activation. To perform ALR with cPM pre-activation, the cPM muscle was activated by raising the contralateral heel 1 inch from the surface of the table to activate the cPM. The activation of the cPM muscle was confirmed by EMG feedback before participants performed the ALR. All exercises were performed in a random order. Data were analyzed using SPSS for Windows software (ver. 20.0; SPSS Inc., Chicago, IL, USA). To assess the normality of the data, the Kolmogorov–Smirnov test was used. Differences in the EMG activity of the abdominal muscles, and in pelvic rotation, between conventional ALR and ALR with cPM pre-activation were evaluated using paired t-tests. The level of significance was set at α=0.05.
RESULTS
The EMG activities of the RA, EO, and IO were significantly greater during ALR with cPM pre-activation (21.14 ± 4.13%; 15.13 ± 3.11%; 18.85 ± 6.12%, respectively) than during conventional ALR (8.12 ± 6.14%; 9.17 ± 7.16%; 12.11 ± 3.63%, respectively) (p˂0.05). Pelvic rotation during ALR with cPM pre-activation (2.17 ± 1.33°) was significantly reduced compared to that during conventional ALR (7.24 ± 3.15°) (p˂0.05).
DISCUSSION
The results of this study showed that the EMG activities of the RA, EO, and IO were significantly greater during ALR with cPM pre-activation compared to the values during conventional ALR (p<0.05). Conventional ALR can cause unwanted compensatory movements due to insufficient muscle activation in the abdominal region. Co-contraction of the abdominal muscles with cPM pre-activation during ALR would be more effective to stabilize the lumbopelvic region5). Increased abdominal muscle activity can be induced by slightly raising the contralateral heel to contract the cPM. Furthermore, the increased load transfer from the pelvis achieved by slight contralateral heel raising may contribute to the occurrence of abdominal co-contraction, increasing external resistance. This means of intervention to activate the abdominal muscles along with cPM can be helpful to stabilize the pelvis during ALR. In this study, pelvic rotation during ALR with cPM pre-activation was significantly reduced compared to ALR performed in the conventional manner (p˂0.05). The origin of the PM is within the body and transverse processes of the lumbar spine. Therefore, contraction of PM can contribute to stabilization of the lumbopelvic region during ALR2, 6). The optimal movement pattern for the lumbopelvic region during ALR requires that the pelvic structure be controlled and remain in a neutral position via activation of the muscles surrounding the area. Therefore, cPM pre-activation during ALR can be recommended to minimize pelvic rotational compensation with increased abdominal muscle contraction. This study had some limitations. First, it used healthy participants in a laboratory setting. Second, the surface EMG electrodes for abdominal muscles have cross-talk effects. Third, a fine wire EMG was not used for a deep muscle such as PM.
Funding
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017R1C1B5076172).
Conflict of interest
None.
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