Expanding our view of the spine system

Reeves, N. Peter; Cholewicki, Jacek

doi:10.1007/s00586-009-1220-5

Cited by 18 publications

(9 citation statements)

References 4 publications

(3 reference statements)

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“…We have shown that two contributing factors to the dynamic stability of human kinematics are: (1) the amount (magnitude) of spine rotational stiffness, and (2) the local dynamic stability of muscle activation, force, and stiffness. During lifting, the controlled variable may be considered the kine matic movement and stability of the torso and/or box, and the con tributing factors to this control are plant stiffness, damping, and nervous system mediated feedback control [2,34], Thus, although we have considered stiffness and feedback related factors as well as the full dynamic outputs through these two research studies, we have yet to consider the full dynamics of the control system (i.e., damping inputs) and how this interacts with the other factors. This damping effect, which could play a larger role with increased movement rate and velocity, could thus help explain our previ ously reported reduced agreement between stiffness and dynamic stability [11], and should be explored in the future.…”

Section: Discussionmentioning

confidence: 99%

Local Dynamic Stability of Spine Muscle Activation and Stiffness Patterns During Repetitive Lifting

Graham

Brown

2014

Journal of Biomechanical Engineering

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To facilitate stable trunk kinematics, humans must generate appropriate motor patterns to effectively control muscle force and stiffness and respond to biomechanical perturbations and/or neuromuscular control errors. Thus, it is important to understand physiological variables such as muscle force and stiffness, and how these relate to the downstream production of stable spine and trunk movements. This study was designed to assess the local dynamic stability of spine muscle activation and rotational stiffness patterns using Lyapunov analyses, and relationships to the local dynamic stability of resulting spine kinematics, during repetitive lifting and lowering at varying combinations of lifting load and rate. With an increase in the load lifted at a constant rate there was a trend for decreased local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness; although the only significant change was for the full state space muscle activation stability (p < 0.05). With an increase in lifting rate with a constant load there was a significant decrease in the local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness (p ≤ 0.001 for all measures). These novel findings suggest that the stability of motor inputs and the muscular contributions to spine rotational stiffness can be altered by external task demands (load and lifting rate), and therefore are important variables to consider when assessing the stability of the resulting kinematics.

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Section: Discussionmentioning

confidence: 99%

Local Dynamic Stability of Spine Muscle Activation and Stiffness Patterns During Repetitive Lifting

Graham

Brown

2014

Journal of Biomechanical Engineering

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“…As the task became more challenging, the level of activation in the agonist muscles increased proportionally. Given that the force applied to the cart handle is regulated by the stick's angular position and velocity (Reeves and Cholewicki 2010), it is not surprising that muscle activation in the agonist increased as the task became more challenging. More agonist muscle activation is required in accelerating the cart when the task becomes more challenging, but this is only true for the agonist.…”

Section: Discussionmentioning

confidence: 99%

Limits in motor control bandwidth during stick balancing

Reeves

Pathak

Popovich

et al. 2013

Journal of Neurophysiology

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Why can we balance a yardstick but not a pencil on the tip of our finger? As with other physical systems, human motor control has constraints, referred to as bandwidth, which restricts the range of frequency over which the system can operate within some tolerated level of error. To investigate control bandwidth, the natural frequency of a stick used during a stick-balancing task was modified by adjusting the height of a mass attached to the stick. The ability to successfully balance the stick with the mass positioned at four different heights was determined. In addition, electromyographic signals from forearm and trunk muscles were recorded during the trials. We hypothesized that 1) the probability of successfully balancing would decrease as mass height decreased; and 2) the level of muscle activation in both agonist and antagonist would increase as the natural frequency of the stick increased. Results showed that as the mass height decreased the probability of successfully balancing the stick decreased. Changes in the probability of success with respect to mass height showed a threshold effect, suggesting that limits in human control bandwidth were approached at the lowest mass height. Also, the level of muscle activation in both the agonist and antagonist of the forearm and trunk increased linearly as the natural frequency of the stick increased. These changes in muscle activation suggest that the central nervous system adapts muscle activation to task dynamics, possibly to improve control bandwidth.

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“…[13][14][15] Anders Bergmark, from Sweden, pioneered biomechanical research that formalized the concept of spine stability in a muscular system. [16][17][18] A mathematical spine model was proposed that possessed stiffness characteristics and represented 40 muscle attachments that could create virtual moments around individual spine joint segments. He formulated the concepts of energy wells, stiffness, stability and instability in this model in which the spine was visualized as a simple inverted pendulum.…”

Section: What Do We Understand By Biomechanical 'Spine Instability'?mentioning

confidence: 99%

Reviewing Complex Static-Dynamic Concepts of Spine Stability: Does the Spine Care Only to Be Stiff to Be Stable?

Mahato

2019

J Morphol Sci

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Background Changes in the load-displacement relationship in spine segments suggesting alterations in biomechanical stiffness may not yield significant clinical information. Changes in Spine stiffness may arise secondary to neuro-muscular adjustments in the para-spinal muscles and may not be associated with physical anatomical laxity or motion restrictions at segmental articulations. Segmental stiffness may vary dynamically at different zones within the range-of-motion, suggesting a non-linear load-displacement relationship during motion. There is no linear, mechanistic relationship between spine pain and biomechanical markers of spine instability. Objective To review diagnostic assessment approaches of spine instability based on palpatory techniques, end-of-range radiography and imaging in light of our current understanding of biomechanical spine stability. Method The Medline and PubMed databases were screened for primary medical and engineering research articles and reviews on spine stability. Information related to bio-mechanical concepts and clinical decision-making were extracted and synthesized. Spine stability was described in two classical forms, the structural (anatomical) and the functional (physiological), the implications of static and dynamic instability was described in terms of biomechanical and mathematical models used to understand etiology of non-specific back pain. Results Evidence supports the view that dynamic adaptations in the load-displacement relationship of the spine may be resistive or assistive, depending on task-specific movements. Diagnosis of instability is based on structural and functional integrity of the segments in a static or dynamic context. Conclusion Development of specific criteria to define clinical spine stability, compatible with system-based biomechanical concept of spine stiffness, is an ongoing topic in clinical and basic science research.

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Expanding our view of the spine system

Cited by 18 publications

References 4 publications

Local Dynamic Stability of Spine Muscle Activation and Stiffness Patterns During Repetitive Lifting

Local Dynamic Stability of Spine Muscle Activation and Stiffness Patterns During Repetitive Lifting

Limits in motor control bandwidth during stick balancing

Reviewing Complex Static-Dynamic Concepts of Spine Stability: Does the Spine Care Only to Be Stiff to Be Stable?

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