2011 October ; 30(5): 869–888. doi:10.1016/j.humov.2011.06.002. | Nicholas Stergiou1,2,* and Leslie M. Decker1
This review explores the relationship between human movement variability and nonlinear dynamics, highlighting the importance of variability in understanding movement dysfunction. The concept of variability and nonlinear dynamics measures are crucial for evaluating movement patterns, which can reveal optimal states for healthy and functional movement. Variability is characterized by a chaotic structure, and deviations from this state can lead to either overly rigid or noisy and unstable systems, both of which reduce adaptability to perturbations.
The review discusses three prominent theories: the Generalized Motor Program Theory (GMPT), the Uncontrolled Manifold (UCM) hypothesis, and the Dynamical Systems Theory (DST). These theories explain how variability is controlled during skill acquisition, the role of motor redundancy, and the self-organizing nature of biological systems. Recent studies using advanced tools like entropic measures and fractal analysis have shown that temporal variations in biological signals exhibit deterministic patterns, which can provide insights into the control of physiological systems.
The review also addresses the misconception that increased variability always equates to instability. Instead, it suggests that variability and stability are distinct properties within the motor control process. Nonlinear measures like the largest Lyapunov exponent and approximate entropy can quantify the structure and organization of variations in time series data, providing a more comprehensive understanding of movement control.
Experimental work from the authors' laboratory supports these theoretical frameworks. Studies on infant motor development and sports medicine, such as anterior cruciate ligament (ACL) injuries, demonstrate how nonlinear dynamics can reveal underlying control strategies and inform therapeutic interventions. For example, ACL deficiency is associated with reduced variability, leading to increased rigidity and potential long-term joint health issues. ACL reconstruction can restore some variability but may not fully restore the optimal state of variability.
Overall, the review emphasizes the importance of variability in human movement and the need for a more nuanced understanding of its role in health and pathology.This review explores the relationship between human movement variability and nonlinear dynamics, highlighting the importance of variability in understanding movement dysfunction. The concept of variability and nonlinear dynamics measures are crucial for evaluating movement patterns, which can reveal optimal states for healthy and functional movement. Variability is characterized by a chaotic structure, and deviations from this state can lead to either overly rigid or noisy and unstable systems, both of which reduce adaptability to perturbations.
The review discusses three prominent theories: the Generalized Motor Program Theory (GMPT), the Uncontrolled Manifold (UCM) hypothesis, and the Dynamical Systems Theory (DST). These theories explain how variability is controlled during skill acquisition, the role of motor redundancy, and the self-organizing nature of biological systems. Recent studies using advanced tools like entropic measures and fractal analysis have shown that temporal variations in biological signals exhibit deterministic patterns, which can provide insights into the control of physiological systems.
The review also addresses the misconception that increased variability always equates to instability. Instead, it suggests that variability and stability are distinct properties within the motor control process. Nonlinear measures like the largest Lyapunov exponent and approximate entropy can quantify the structure and organization of variations in time series data, providing a more comprehensive understanding of movement control.
Experimental work from the authors' laboratory supports these theoretical frameworks. Studies on infant motor development and sports medicine, such as anterior cruciate ligament (ACL) injuries, demonstrate how nonlinear dynamics can reveal underlying control strategies and inform therapeutic interventions. For example, ACL deficiency is associated with reduced variability, leading to increased rigidity and potential long-term joint health issues. ACL reconstruction can restore some variability but may not fully restore the optimal state of variability.
Overall, the review emphasizes the importance of variability in human movement and the need for a more nuanced understanding of its role in health and pathology.