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.
    No preview · Article · Nov 2014 · Journal of Biomechanics
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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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    • "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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