Trunk muscle co-activation using functional electrical stimulation modifies center of pressure fluctuations during quiet sitting by increasing trunk stiffness (original) (raw)
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Technology and Health Care, 2021
BACKGROUND: Balance control is a leading component of human motor activities and its impairment is associated with an increased risk of falling, lower back pain due to impaired motor control mechanism. Prolonged sitting position at workplace is one of the risk factors of reduced postural control and lower back pain. OBJECTIVE: To evaluate theta and alpha waves cortical activity, trunk muscles activity and kinematics in static sitting, dynamic sitting on different platforms: simple wobble board (WB) and wobble board on bearing surface (WBB). METHODS: The kinematics of body segments, electromyography of five trunk muscles, electroencephalography of 32 scalp electrodes were measured during balance tasks in sitting position for 17 subjects with continuous seated position at workplace. RESULTS: Cortical power on WBB1 increase in fronto – central (p< 0.05) region while on WBB2 increase in centro – parietal region (p< 0.05). WBB2 increase more muscles compared with WB2. The amplitude...
Electromyographic response of the trunk muscles to postural perturbation in sitting subjects
Journal of Electromyography and Kinesiology, 1998
Electromyographic (EMG) patterns of the trunk muscles were investigated during balance perturbations in a sitting position. Five healthy subjects (two females and three males, mean age 24.4 yr) were seated on a platform allowing rotational perturbations in the frontal and sagittal planes. Each of the forward, backward, right and left perturbations were delivered with and without expectation at the velocities 8°s Ϫ 1 (SD ± 4°s Ϫ 1 ) and 26°s Ϫ 1 (SD ± 6°s Ϫ 1 ). The fast expected and unexpected perturbations were compared in blindfolded subjects. In the slow perturbations the effect of a blindfold on the balance reactions was tested. The root mean square (RMS) EMG signals from 12 trunk muscles were recorded and analysed to determine the EMG magnitudes. During the forward and backward rotations there was always a symmetrical EMG pattern between corresponding muscles on the right and left sides. A reciprocal phasic EMG activity between the left and right back muscles was found during frontal rotations. No reciprocal phasic activity was found in the abdominal muscles. Neither verbal instruction about the upcoming perturbation nor the blindfold changed the activation patterns.
Multidirectional quantification of trunk stiffness and damping during unloaded natural sitting
Medical Engineering & Physics, 2014
Trunk instability during sitting is a major problem following neuromuscular injuries such as stroke and spinal cord injury. In order to develop new strategies for alleviating this problem, a better understanding of the intrinsic contributions of the healthy trunk to sitting control is needed. As such, this study set out to propose and validate a novel methodology for determining multidirectional trunk stiffness during sitting using randomized transient perturbations. Fifteen healthy individuals sitting naturally on a custom-made seat were randomly perturbed in eight horizontal directions. Trunk stiffness and damping were quantified using force and trunk kinematics in combination with translational and torsional models of a mass-spring-damper system. The results indicate that stiffness and damping of the healthy trunk are roughly symmetrical between the two body sides. Moreover, both quantities are smallest in the anterior and largest in the lateral directions. In conclusion, a novel protocol for identifying intrinsic trunk stiffness and damping has been developed, eliminating anticipation effects with respect to perturbation timing and direction. Subsequent studies will use these findings as a reference for quantifying trunk stiffness and damping in individuals with various neuromuscular disorders, but also for assessing whether neuroprostheses could increase upper body stiffness and, hence, stability.
Evaluation of the Flexion Relaxation Phenomenon of the Trunk Muscles in Sitting
Spine, 2006
Study Design. A normative, single-group study was conducted. Objective. To investigate the flexion relaxation phenomenon in the thoraco-lumbopelvic muscles among a pain-free population when moving from an upright to a slump sitting posture. Summary of Background Data. The presence of the flexion relaxation phenomenon (FRP) of the back muscles is well documented at end-range spinal flexion when standing. This phenomenon is commonly found disrupted in low back subjects. However, whether FRP occurs in sitting remains controversial. Methods. The sample consisted of 24 healthy painfree adults. Surface electromyography was used to measure activity in the superficial lumbar multifidus (SLM), the thoracic erector spinae (TES), and the transverse fibers of the internal oblique (IO) muscles while subjects moved from an erect to a slump sitting posture. An electromagnetic motion-tracking device simultaneously measured thoracolumbar kinematics during this task. Results. There was a significant decrease in both the SLM and the IO activity when moving from an erect to a slump sitting posture (P ϭ 0.001 and P ϭ 0.004, respectively), indicating the presence of FRP. TES activity was highly variable. While 13 subjects exhibited an increase in activity (P ϭ 0.001), 11 demonstrated a decrease in activity (P ϭ 0.001), indicating the presence of FRP. FRP occurred in the mid-range of spinal flexion for the SLM, IO and TES when present. Conclusion. The findings show that the SLM and the IO are facilitated in neutral lordotic sitting postures and exhibit FRP at mid range flexion while moving from upright sitting to slump sitting. These findings show that FRP in sitting differs from that in standing. Variable motor patterns (activation or FRP) of the TES were observed. These findings suggest that sustaining mid to end-range flexed sitting spinal postures result in relaxation of the spinal stabilizing muscles.
The purpose of this study was to evaluate differences in trunk muscles’ activation and perceived sitting discomfort during prolonged office-computer work on a standard office chair and a chair with unstable seat Active Chair®. Fourteen healthy volunteers (6 men, 8 women), aged 22.4 ± 2.2 years, body mass 65.0 ± 11.8 kg; body height 169.9 ± 11.6 m, performed four 15-minute long computerized office tasks. While performing the tasks electromyography (EMG) activity of eight trunk muscles (left and right lower trapezius (LT), erector spinae (ES), rectus abdominis (RA) and obliquus externus (OE)) and the overall level of perceived sitting discomfort at the beginning and after each task were measured and analyzed. The results showed that the average EMG activity of back and abdominal muscles during 1 hour of work on the Active Chair® was only 1.35 % of the maximum voluntary contraction (MVC) and was not significantly different from the standard chair (p = .323). On the Active Chair® the right ES activity was significantly lower (p = .002), while the activity of the left OE was significantly higher (p = .026) compared to the standard office chair. The overall level of perceived sitting discomfort on the Active Chair® at the beginning (40.2 ± 26.0 mm; p = .001) and at the end (65.7 ± 25.7 mm; p < .001) of 1-hour work was significantly higher compared to the standard office chair at the end of 1-hour work (9.1 mm). However, the discomfort level on the Active Chair® increased significantly only after 45 minutes (61.0 ± 20.9 mm; p = .024). It could be concluded that sitting on the Active Chair® increases the activity of some muscles, but it is relatively low considering muscles’ activity during MVC. The overall level of sitting discomfort on the Active Chair® is higher than on a standard office chair, which is somehow expected for these types of chairs, yet it could still be improved.
2013
The level and completeness of spinal cord injury (SCI) above the first lumbar vertebra determine the degree of multi-system impairments including altered respiratory function and decreased capacity to maintain upright posture and seated postural stability in humans. Both systems were studied in able-bodied (AB) subjects and individuals with tetraplegia to explore the potential of functional electrical stimulation (FES) as a neuroprosthesis for seated postural control without compromising respiratory function. Data for AB participants (n=10) indicated higher tidal volumes, greater trunk extensor muscle activity, and different values of seated postural stability in upright sitting compared to slouch sitting. In three case studies of individuals with tetraplegia, surface FES was applied to trunk muscles. Changes in tidal volume, respiratory rate, and seated postural stability were case specific. These studies inform the development of a strategy for noninvasive FES as a neuroprosthesis for sitting balance while preserving respiratory function in individuals with SCI. iii Acknowledgments I would like to acknowledge my supervisor, Professor Molly Verrier, for accepting me as a student of physiology, introducing me to the field of rehabilitation, building my knowledge of human biomechanics and dynamics, and teaching me a few valuable life lessons along the way. I would like to thank my co-supervisor, Dr. Milos Popovic, and members of my advisory committee, Drs. Dina Brooks and Barry Sessle, for providing insightful commentary during the conceptualization and realization of this project.
International Journal of Environmental Research and Public Health
Employing dynamic office chairs might increase the physical (micro-) activity during prolonged office sitting. We investigated whether a dynamic BioSwing® chair increases chair sway and alters trunk muscle activation. Twenty-six healthy young adults performed four office tasks (reading, calling, typing, hand writing) and transitions between these tasks while sitting on a dynamic and on a static office chair. For all task-transitions, chair sway was higher in the dynamic condition (p < 0.05). Muscle activation changes were small with lower mean activity of the left obliquus internus during hand writing (p = 0.07), lower mean activity of the right erector spinae during the task-transition calling to hand writing (p = 0.036), and higher mean activity of the left erector spinae during the task-transition reading to calling (p = 0.07) on the dynamic chair. These results indicate that an increased BioSwing® chair sway only selectively alters trunk muscle activation. Adjustments of chai...
The effects of trunk stiffness on postural control during unstable seated balance
Experimental Brain Research, 2006
This paper focused on the relationship between trunk stiVness and postural control during unstable seated balancing. We hypothesized that an increase in trunk stiVness would degrade postural control, and further hypothesized that signal dependent noise (SDN), resulting in increased muscle force variability, was responsible for this impairment. Ten subjects balanced on an unstable seat during four randomized conditions: normal balancing (control condition), trunk muscle co-activation (active stiVness), arm muscle coactivation (attention control), and belt (passive stiVness). Center of pressure (CoP) and EMG data were collected during three 20 s trials. Postural control was quantiWed by CoP velocity (total path divided by sample time in seconds). Trunk muscle co-activation resulted in signiWcantly higher CoP velocity than the control (P < 0.001) and arm co-activation (P < 0.001) conditions. EMG data conWrmed that the trunk co-activation condition had signiWcantly higher muscle activity than the control (P = 0.001) and arm co-activation (P = 0.001) conditions. The belt condition, which increases passive trunk stiVness, showed no degraded postural control, but interestingly produced slightly lower levels of trunk muscle activity than the control condition (P < 0.001). Increased active trunk stiVness from muscle co-activation degraded postural control. Since the arm co-activa-tion condition showed no impairment, attention demands cannot explain this result. Furthermore, since passive trunk stiVness from wearing a belt did not aVect performance, it is believed that SDN from increased trunk muscle recruitment, and not an altered postural control strategy from increased joint stiVness, was responsible for the impairment.