Kinematics-based prediction of trunk muscle activity in response to multi-directional perturbations during sitting

The effect of electromyography triggered electrical stimulation to abdominal muscles on sitting balance, respiratory functions, and abdominal muscle thickness in complete spinal cord injury: a randomized controlled trial

Complete thoracic spinal cord injury (SCI) results in a loss of innervation to the abdominal muscles, which affects trunk stability and performance of activities of daily living from a sitting position. Respiratory function is also affected, leading to frequent pulmonary complications. Given the importance of trunk stability and respiratory function, we investigated the effects of electromyography triggered electrical stimulation (EMG-ES) applied to the abdominal muscles on sitting balance, respiratory functions and abdominal muscle thickness in individuals with complete thoracic SCI. This randomized controlled study included 34 participants with complete thoracic SCI who were randomly allocated to the experimental group ( n  = 17) and the control group ( n  = 17). During the 4-week intervention period, the experimental group received EMG-ES to their abdominal muscles, while the control group received isometric abdominal exercises three times per week. Both groups continued with their routine rehabilitation program (active or passive range of motion exercises, stretching, and balance coordination exercises). The primary outcome measures were the modified functional reach test (mFRT) and trunk control test (TCT). Secondary outcome measures included a pulmonary function test (PFT) and the bilateral abdominal muscle thicknesses using ultrasonography. At the end of the study, the experimental group showed significantly greater improvements in both primary outcomes. The mean difference in pre-post changes between the groups for the mFRT area was 242.8 cm² [95% confidence interval (CI): 181.3-329.8; effect size 0.92; P  < 0.001] and 5.0 points for TCT (95% CI: 3.9-6.0; effect size 0.98, P  < 0.001). The increase in the abdominal muscle thickness was also significantly greater in the experimental group ( P  < 0.001) without significant differences in the PFT ( P  > 0.05). We conclude that adding EMG-ES of abdominal muscles may further improve sitting balance and abdominal muscle thickness in individuals with complete thoracic SCI.

Nonlinear Response of Human Trunk Musculature Explains Neuromuscular Stabilization Mechanisms in Sitting Posture

OBJECTIVE

Determining the roles of underlying mechanisms involved in stabilizing the human trunk during sitting is a fundamental challenge in human motor control. However, distinguishing their roles requires understanding their complex interrelations and describing them with physiologically meaningful neuromechanical parameters. The literature has shown that such mechanistic understanding contributes to diagnosing and improving impaired balance as well as developing assistive technologies for restoring trunk stability. This study aimed to provide a comprehensive characterization of the underlying neuromuscular stabilization mechanisms involved in human sitting.

APPROACH

This study characterized passive and active stabilization mechanisms involved in seated stability by identifying a nonlinear neuromechanical physiologically-meaningful model in ten able-bodied individuals during perturbed sitting via an adaptive unscented Kalman filter to account for the nonlinear time-varying process and measurement noises.

MAIN RESULTS

We observed that the passive mechanism provided instant resistance against gravitational disturbances, whereas the active mechanism provided delayed complementary phasic response against external disturbances by activating appropriate trunk muscles while showing non-isometric behavior. The model predicted the trunk sway behavior during perturbed sitting with high accuracy and correlation (average: 0.0007 [rad2] and 86.77%). This allows a better mechanistic understanding of the roles of passive and active stabilization mechanisms involved in sitting.

SIGNIFICANCE

Our characterization approach accounts for the inherently nonlinear behavior of the neuromuscular mechanisms and physiological uncertainties, while allowing for real-time tracking and correction of parameters' variations due to external disturbances and muscle fatigue. The outcome of our research, for the first time, (1) allows a better mechanistic understanding of the roles of passive and active stabilization mechanisms involved in sitting; (2) enables objective evaluation and targeted rehabilitative interventions for impaired balance; facilitate bio-inspired designs of assistive technologies, and (3) opens new horizons in mathematical identification of neuromechanical mechanisms employed in the stable control of human body postures and motions.

Influence of Anterior-Posterior External Surface Perturbation on Trunk Stability During Abdominal Stabilization Strategies While Sitting

Background

Spinal and pelvic injuries during an unexpected perturbation are closely related to spinal stability, which is known to be controlled by abdominal stabilization maneuvers. This study aimed to evaluate the effects of unexpected perturbations on trunk stability and abdominal stabilization strategies in 42 sedentary adults while sitting.

Material/Methods

Abdominal stabilization strategies consisted of bracing and hollowing maneuvers. Abdominal bracing maneuvers (ABM) were focused on the abdominal wall muscles [inferior oblique (IO), exterior oblique (EO)], and abdominal hollowing maneuvers (AHM) were focused on deep muscle (TrA) activation. The subjects were instructed in abdominal stabilization maneuvers. Afterward, subjects were seated in a chair that could be moved forward or backward suddenly with the support surface.

Results

Angular displacements of the upper thorax, lower thorax, and lumbopelvic during unexpected perturbation, with different abdominal stabilization maneuvers, were measured. During forward perturbation (d=0.71, F=10.324, P=0.001) and backward perturbation in high speed (d=0.62, F=9.265, P=0.011), there were significant differences in angular displacements of the upper thorax between hollowing and bracing maneuvers. Additionally, significant differences were found in the lumbopelvic angular displacement between the hollowing and bracing maneuvers (d=0.62, F=4.071, P=0.044).

Conclusions

Our findings indicate that the ABM is a better stabilizing technique for the upper thorax, and the AHM is a better stabilizing technique for the lumbopelvic region during unexpected perturbations at high speed in the seated position.

Inter-Day Reliability and Changes of Surface Electromyography on Two Postural Muscles Throughout 12 Weeks of Hippotherapy on Patients with Cerebral Palsy: A Pilot Study

Cerebral palsy (CP) is an umbrella term covering a group of permanent developmental disorders of movement and posture characterized by highly variable clinical features. The aim of this study was to assess the short-term and mid-term effects of neurorehabilitation via hippotherapy on the contractile properties of two key postural muscles during functional sitting in such patients. Thirty-minute hippotherapy sessions were conducted biweekly for 12 weeks in 18 patients (18.1 ± 5.7 years old). Surface electromyography (EMG) was implemented bilaterally in rectus abdominis and adductor magnus. We quantitatively analyzed the amplitude of EMG signals in the time domain and its spectral characteristics in the frequency domain. EMGs were recorded at the beginning and end of each session on day one and at week six and week twelve. Statistical analysis revealed a substantial inter-day reliability of the EMG signals for both muscles, validating the methodological approach. To a lesser extent, while beyond the scope of the current study, quantitative changes suggested a more selective recruitment/contractile properties’ shift of the examined muscles. Exploring postural control during functional activities would contribute to understanding the relationship between structural impairment, activity performance and patient capabilities, allowing the design of neurorehabilitation programs aimed at improving postural and functional skills according to each individual’s needs. The present study provides basic quantitative data supporting the body of scientific evidence making hippotherapy an approach of choice for CP neurorehabilitation.