Trunk response analysis under sudden forward perturbations using a kinematics-driven model

Department of Mechanical Engineering, Ecole Polytechnique, Station "centre-ville", Montreal, Quebec, Canada.
Journal of Biomechanics (Impact Factor: 2.75). 05/2009; 42(9):1193-200. DOI: 10.1016/j.jbiomech.2009.03.014
Source: PubMed


Accurate quantification of the trunk transient response to sudden loading is crucial in prevention, evaluation, rehabilitation and training programs. An iterative dynamic kinematics-driven approach was used to evaluate the temporal variation of trunk muscle forces, internal loads and stability under sudden application of an anterior horizontal load. The input kinematics is hypothesized to embed basic dynamic characteristics of the system that can be decoded by our kinematics-driven approach. The model employs temporal variation of applied load, trunk forward displacement and surface EMG of select muscles measured on two healthy and one chronic low-back pain subjects to a sudden load. A finite element model accounting for measured kinematics, nonlinear passive properties of spine, detailed trunk musculature with wrapping of global extensor muscles, gravity load and trunk biodynamic characteristics is used to estimate the response under measured sudden load. Results demonstrate a delay of approximately 200ms in extensor muscle activation in response to sudden loading. Net moment and spinal loads substantially increase as muscles are recruited to control the trunk under sudden load. As a result and due also to the trunk flexion, system stability significantly improves. The reliability of the kinematics-driven approach in estimating the trunk response while decoding measured kinematics is demonstrated. Estimated large spinal loads highlight the risk of injury that likely further increases under larger perturbations, muscle fatigue and longer delays in activation.

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    • " AGLR method for individual muscles of the same subject 4 ( LG : 137 ms ( C4 ) to 196 ms ( C2 ) , IC : 137 ms ( C4 ) to 202 ms ( C2 ) ) . It is to be noted that the forward dynamic latency was obtained through computed kinematics while AGLR latency was obtained from estimated muscle forces . These values are in agreement with earlier estimations ( Bazrgari et al . , 2009 ) . Predictions demonstrated the significant influence of sudden load magnitude on biomechanical variables . Expectedly , larger sudden load magnitude ( 100 N vs 50 N ) increased active muscle forces at all levels ( Fig . 4e ) in agreement with our recorded EMG Reflex - Peak ( Fig . 4d ) and earlier findings ( Granata et al . , 2004 ; K"
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    ABSTRACT: Understanding the central nervous system (CNS) response strategy to trunk perturbations could help in prevention of back injuries and development of rehabilitation and treatment programs. This study aimed to investigate biomechanical response of the trunk musculoskeletal system under sudden forward loads, accounting for pre-perturbation conditions (preloading, initial posture and abdominal antagonistic coactivation) and perturbation magnitudes. Using a trunk kinematics-driven iterative finite element (FE) model, temporal profiles of measured kinematics and external load along with subjects’ weights were prescribed to predict thoracolumbar muscle forces/latencies and spinal loads for twelve healthy subjects when tested in six conditions during pre- and post-perturbation periods. Results demonstrated that preloading the trunk significantly (i.e., p<0.05) increased pre-perturbation back muscle forces but significantly decreased post-perturbation peak muscle active forces and muscle latencies. Initial trunk flexion significantly increased muscle active and passive forces before the perturbation and their peak values after the perturbation, which in turn caused much larger spinal loads. Abdominal muscles antagonistic pre-activation did not alter the internal variables investigated in this study. Increase in sudden applied load increased muscle reflex activities and spinal forces; a 50 N increase in sudden load (i.e., when comparing 50 N to 100 N) increased the L5-S1 compression force by 1327 N under 5 N preload and by 1374 N under 50 N preload. Overall, forces on the spine and hence risk of failure substantially increased in sudden forward loading when the magnitude of sudden load increased and when the trunk was initially in a flexed posture. In contrast, a higher initial preload diminished reflex latencies and compression forces.
    Journal of Biomechanics 11/2014; 48(1). DOI:10.1016/j.jbiomech.2014.11.006 · 2.75 Impact Factor
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    • "The sudden application or removal of loads has been used to gain knowledge of how the neuromuscular system coordinates muscle activity to maintain rotational impedance. Previously, researchers used sudden loading or unloading protocols to perturb various joint such as the lumbar spine (Bazrgari et al., 2009; Brown et al., 2006; Cholewicki et al., 2005; Granata et al., 2001), and the knee (Shultz et al., 2000) followed by the quantification of the muscular response to the perturbation. In addition to the sudden loading/unloading protocol, researchers added a further dimension to challenge the neuromuscular system by altering subjects' knowledge of perturbation timing. "
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    ABSTRACT: Previous research has suggested that muscle forces, generated by reflexes, contribute to joint stability prior to the more coordinated voluntary muscle forces. The purpose of the current study was to quantify the behaviour of the leg muscles, through the calculation of individual muscle contributions to joint rotational impedance (MJRI), with a specific interest in the neuromuscular contribution in the period following shortly after a sudden knee extension perturbation. The knee was selected as an in vivo system to represent an inverted pendulum model. Kinematic and sEMG data were collected while subjects were in a prone position and exposed to sudden knee extension perturbations. A biomechanical model was used to estimate muscle forces and moments about the knee and these data were then used to calculate instantaneous MJRI. Data indicated that pre-voluntary muscle forces do contribute significantly to MJRI following a sudden knee extension perturbation as there was a 40% increase in total MJRI in the flexion/extension and valgus/varus axes immediately following the perturbation, suggesting their importance in stabilizing the joint immediately after a disturbance. Additionally, knowledge of perturbation timing was shown to increase anticipatory MJRI levels, pre-perturbation (p<0.05), indicating that it is advantageous for the neuromuscular system to prepare for a sudden disturbance. In conclusion, the data show that the neuromuscular feedback system significantly contributes to MJRI and it is believed that this behaviour enhances joint impedance following a sudden knee extension perturbation.
    Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 12/2011; 22(2):243-50. DOI:10.1016/j.jelekin.2011.11.003 · 1.65 Impact Factor
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    • "Studies have advocated efficient neuromuscular control for trunk stability [7], accurate trunk muscle recruitment patterns for controlling spinal load in relevant to given task and posture [8,9] for impaired trunk control[10] and poor balance[11] associated with CLBP. Further correlation between impaired postural control and delayed muscle response time in twelve major trunk muscles was also reported for patients with CLBP [11]. "
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    ABSTRACT: The purpose of the present study was to examine the differential effect of core stability exercise training and conventional physiotherapy regime on altered postural control parameters in patients with chronic low back pain (CLBP). As heterogeneity in CLBP population moderates the effect of intervention on outcomes, in this study, interventions approaches were used based on sub-groups of CLBP. This was an allocation concealed, blinded, sequential and pragmatic control trial. Three groups of participants were investigated during postural perturbations: 1) CLBP patients with movement impairment (n = 15, MI group) randomized to conventional physiotherapy regime 2) fifteen CLBP patients with control impairment randomized to core stability group (CI group) and 3) fifteen healthy controls (HC). The MI group did not show any significant changes in postural control parameters after the intervention period however they improved significantly in disability scores and fear avoidance belief questionnaire work score (P < 0.05). The CI group showed significant improvements in Fx, Fz, and My variables (p < 0.013, p < 0.006, and p < 0.002 respectively with larger effect sizes: Hedges's g > 0.8) after 8 weeks of core stability exercises for the adjusted p values. Postural control parameters of HC group were analyzed independently with pre and post postural control parameters of CI and MI group. This revealed the significant improvements in postural control parameters in CI group compared to MI group indicating the specific adaptation to the core stability exercises in CI group. Though the disability scores were reduced significantly in CI and MI groups (p < 0.001), the post intervention scores between groups were not found significant (p < 0.288). Twenty percentage absolute risk reduction in flare-up rates during intervention was found in CI group (95% CI: 0.69-0.98). In this study core stability exercise group demonstrated significant improvements after intervention in ground reaction forces (Fz, Mz; g > 0.8) indicating changes in load transfer patterns during perturbation similar to HC group. UTRN095032158-06012009423714.
    Sports Medicine Arthroscopy Rehabilitation Therapy & Technology 05/2010; 2(1):13. DOI:10.1186/1758-2555-2-13
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