Hiroshi Osaka

Individuals with chronic low back pain demonstrate delayed onset of the back muscle activity during prone hip extension

Prone hip extension (PHE) is commonly used in the evaluation of the stability of the lumbopelvic region. There is little evidence of difference in muscle activity onset timing between healthy individuals and individuals with chronic low back pain (CLBP) during PHE. The purpose of this study was to determine if individuals with and without CLBP differ in the onset time of the trunk and hip extensor muscles activity during PHE. The participants were 20 patients with CLBP and 20 healthy individuals. Electromyography data of the erector spinae, multifidus, gluteus maximus, and semitendinosus were collected during PHE using a surface electromyograph. Relative differences in the onset times between each muscle and the prime mover (i.e., the semitendinosus) were calculated. The onsets of the bilateral multifidus and contralateral erector spinae were significantly delayed in the CLBP group compared with the healthy group (p<0.001), despite the onset timings of leg movement not being significantly different between the groups. The onset times of the gluteus maximus and ipsilateral erector spinae showed no significant differences between the groups. These results suggest that individuals with CLBP use an altered, and possibly inadequate, trunk muscle recruitment pattern.

Influence of trunk muscle co-contraction on spinal curvature during sitting

BACKGROUND AND PURPOSE Slumped sitting is known to increase disc pressure and aggravate chronic low back pain. In addition, it has been recognized that co-contraction of the deep spine-stabilizing muscles enhances lumbar segmental stability and the sacro-iliac joint. The purpose of this study was to compare the electromyographic (EMG) activity of the trunk muscles and the muscle thickness of the transverse abdominis (TrA) during slumped sitting with the same parameters during co-contraction and investigate how co-contraction influences spinal curvature. SUBJECTS AND METHODS Nine healthy male volunteers participated in the study. EMG signals were recorded during both sitting postures. In order to measure the muscle thickness of the TrA, ultrasound images were captured. While the subjects performed both sitting postures, spinal curvature was measured using a hand-held device. RESULTS Significantly more activity of the trunk muscles, with the exception of the rectus abdominis muscle, and significantly greater muscle thickness of the TrA were observed during co-contraction of the trunk muscles than during slumped sitting. Co-contraction also resulted in significantly increased lumbar lordosis and a greater sacral angle when compared to slumped sitting. CONCLUSION In this study, it was demonstrated that the instructions given to the subjects on co-contraction of the trunk muscles during sitting increased muscle activity with the exception of the rectus abdominis muscle, muscle thickness of the TrA, and lumbar lordosis.

Comparison of spine motion and trunk muscle activity between abdominal hollowing and abdominal bracing maneuvers during prone hip extension.

The aim of this study was to examine the effects of lumbopelvic stabilization maneuvers on spine motion and trunk muscle activity during prone hip extension (PHE). In this study, 14 healthy male volunteers (mean age, 21.2 ± 2.6 years) were instructed to perform PHE without any maneuvers (control), with abdominal hollowing (AH), and with abdominal bracing (AB). Surface electromyography data were collected from the trunk muscles and the lumbopelvic motion was measured. Lumbar extension and anterior pelvic tilt degree were significantly lower in the AH and AB than in the control condition during PHE (p < 0.001). Lumbar extension and anterior pelvic tilt degree did not differ significantly between the AH and AB (p > 0.05). Global muscle group activity such as external obliques was lower in the AH than in the AB. These findings suggest that PHE with AH effectively minimizes unwanted lumbopelvic motion which does not result in global muscle activation.

Effect of Rotational Axis Position of Wheelchair Back Support on Shear Force when Reclining

[Purpose] The purpose of this study was to investigate the influence of the rotational axis position of a reclining wheelchair’s back support on fluctuations in the shear force applied to the buttocks while the back support is reclined. [Subjects] The subjects were 12 healthy adult men. [Methods] The shear force applied to the buttocks was measured using a force plate. This study used two different experimental conditions. The rotational axis of the back support was positioned at the joint between the seat and the back support for the rear-axis condition, and was moved 13 cm forward for the front-axis condition. [Results] With the back support fully reclined, the shear forces were 11.2 ± 0.8%BW and 14.1 ± 2.5%BW under the rear-axis and front-axis conditions, respectively. When returned to an upright position, the shear forces were 17.1 ± 3.1%BW and 13.8 ± 1.7%BW under the rear-axis and front-axis conditions, respectively. Significant differences appeared between the two experimental conditions (p < 0.01). [Conclusion] These results suggest that the shear force value could be changed by altering the position of the back support’s rotational axis during reclining.

Correlation between Peak Expiratory Flow and Abdominal Muscle Thickness

[Purpose] The purpose of this study was to determine whether forced expiration is correlated with abdominal muscle thickness. [Subjects] Twenty-three healthy male volunteers participated in this study. [Methods] The peak expiratory flow (PEF) was obtained using a peak flow meter with subjects in the sitting position. The thicknesses of the right rectus abdominis, external oblique, internal oblique, and transverse abdominis muscles were measured using B-mode ultrasonography at the end of a relaxed expiration in the supine position. [Results] Among the abdominal muscles, only the thickness of the external oblique muscle displayed a significant correlation with PEF. [Conclusion] It appears that the thickness of the external oblique muscle might be associated with PEF during forced expiration.

Influence of distance between the rotation axis of back support and the hip joint on shear force applied to buttocks in a reclining wheelchair's back support.

Purpose: The purpose of this study was to investigate the influence of the distance between the position of the rotation axis of the back support and hip joint on the changes in the shear force applied to the buttocks. Study Design: Repeated-measures design. Methods: The subjects were 11 healthy adult men without leg and/or trunk diseases. The shear force applied to the buttocks was measured using a force plate. This study had three experimental conditions: the position of hip joint was taken as the 3 cm, 6 cm, and 9 cm forward from the standard sitting position. Results: In returning to an upright position of back support, the shear force was 15.0 ± 2.9 %BW in the 3 cm forward condition, 16.7 ± 3.6 %BW in the 6 cm forward condition, and 19.5 ± 5.3 %BW in the 9 cm forward condition. Significant differences appeared between the 9 cm and the other conditions (p < 0.05). Conclusions: The results of this study suggested that the shear force applied to the buttocks changed in reclining back support and an increase in the distance between the axis of rotation of the back support and hip joint led to an increase in the remaining shear force after reclining the back support. Clinical relevance This study shows one of the strategies of seating approach for the prevention of decubitus ulcers. There is possibility of reducing shear force applied to buttocks during and after reclined back support by adjusting the axes of rotation of wheelchair back support.

Mechanism of fluctuation in shear force applied to buttocks during reclining of back support on wheelchair

Purpose: The purpose of this study was to investigate the mechanism of the fluctuation in the shear force applied to the buttocks. Method: The subjects were 11 healthy adult men without leg or trunk diseases. The amount of force applied to the buttocks was measured by using a force plate, and a pressure and shear force sensor was used to measure the timing of the force applied to the back support. Results: The average value of the shear force applied to the buttocks was 9.4 ± 2.4 (%BW) in the initial upright position (IUP), 9.3 ± 1.2 (%BW) in the fully reclined position (FRP), and 15.0 ± 2.9 (%BW) in the returning to an upright position (RUP). Significant differences appeared between the RUP and the other positions. Conclusions: The results of this study suggested that the adjustment of the axes of rotation of the back support and trunk–pelvis and the release of the remaining shear force after the back support is reclined are important for the prevention of decubitus ulcers. Implications for Rehabilitation This study shows one of the strategies of seating approach for the prevention of decubitus ulcers. There is a possibility of reducing shear force applied to buttocks during and after reclined back support by adjusting the axes of rotation of wheelchair back support.

Excitability changes in intracortical neural circuits induced by differentially controlled walking patterns.

Our previous single-pulse transcranial magnetic stimulation (TMS) study revealed that excitability in the motor cortex can be altered by conscious control of walking relative to less conscious normal walking. However, substantial elements and underlying mechanisms for inducing walking-related cortical plasticity are still unknown. Hence, in this study we aimed to examine the characteristics of electromyographic (EMG) recordings obtained during different walking conditions, namely, symmetrical walking (SW), asymmetrical walking 1 (AW1), and asymmetrical walking 2 (AW2), with left to right stance duration ratios of 1:1, 1:2, and 2:1, respectively. Furthermore, we investigated the influence of three types of walking control on subsequent changes in the intracortical neural circuits. Prior to each type of 7-min walking task, EMG analyses of the left tibialis anterior (TA) and soleus (SOL) muscles during walking were performed following approximately 3 min of preparative walking. Paired-pulse TMS was used to measure short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) in the left TA and SOL at baseline, immediately after the 7-min walking task, and 30 min post-task. EMG activity in the TA was significantly increased during AW1 and AW2 compared to during SW, whereas a significant difference in EMG activity of the SOL was observed only between AW1 and AW2. As for intracortical excitability, there was a significant alteration in SICI in the TA between SW and AW1, but not between SW and AW2. For the same amount of walking exercise, we found that the different methods used to control walking patterns induced different excitability changes in SICI. Our research shows that activation patterns associated with controlled leg muscles can alter post-exercise excitability in intracortical circuits. Therefore, how leg muscles are activated in a clinical setting could influence the outcome of walking in patients with stroke.

Influence of Hip Joint Position on Muscle Activity during Prone Hip Extension with Knee Flexion

[Purpose] This study investigated the selective activation of the gluteus maximus during a prone hip extension with knee flexion exercise, with the hip joint in different positions. [Subjects] The subjects were 21 healthy, male volunteers. [Methods] Activities of the right gluteus maximus, right hamstrings, bilateral lumbar erector spinae, and bilateral lumbar multifidus were measured using surface electromyography during a prone hip extension with knee flexion exercise. Measurements were made with the hip joint in each of 3 positions: (1) a neutral hip joint position, (2) an abduction hip joint position, and (3) an abduction with external rotation hip joint position. [Results] Gluteus maximus activity was significantly higher when the hip was in the abduction with external rotation hip joint position than when it was in the neutral hip joint and abduction hip joint positions. Gluteus maximus activity was also significantly higher in the abduction hip joint position than in the neutral hip joint position. Hamstring activity was significantly lower when the hip was in the abduction with external rotation hip joint position than when it was in the neutral hip joint and abduction hip joint positions. [Conclusion] Abduction and external rotation of the hip during prone hip extension with knee flexion exercise selectively activates the gluteus maximus.

Association between trunk acceleration during walking and clinically assessed balance in patients with stroke

BACKGROUND Accelerometers provide information regarding balance and gait, but they are rarely used in clinical settings for stroke patients. Clinically, balance is assessed with simple tests, but their relationships with accelerometry results after stroke are unknown. OBJECTIVE We examined the relationship between accelerometry-assessed gait indices calculated from trunk acceleration and results of the Timed Up and Go (TUG) and Berg Balance Scale (BBS) tests in stroke patients. METHODS Twenty-nine stroke patients completed assessments with the TUG, BBS, and trunk acceleration during walking using a tri-axial accelerometer. The root mean square (RMS), stride regularity (SR), and step symmetry (SS), which indicate gait fluctuations, regularity, and symmetry, respectively, were calculated based on trunk acceleration. These were calculated in the vertical (VT), anteroposterior, and mediolateral directions. A multiple linear regression analysis was performed to determine whether these gait indices contributed independently to TUG and BBS results. RESULTS VT-RMS and VT-SS were significant determinants of TUG, and VT-SS, VT-RMS, and VT-SR were significant determinants of BBS. CONCLUSIONS This study suggested that the gait indices calculated from trunk acceleration that were relevant to balance were those in the VT direction. These may be useful for evaluating dynamic gait balance in patients with stroke.