Movement Variability and the Use of Nonlinear Tools: Principles to Guide Physical Therapist Practice
Regina T Harbourne, Nicholas Stergiou
Phys Ther. Mar 2009; 89(3): 267–282.
This interesting article outlines the need to engage in new and variable function, initially that is ‘unstable’ and through exploration becomes stable…
“If a child has been using training wheels, pedaling and controlling the direction of the bicycle are stable behaviors. However, when the training wheels are removed, the system is perturbed. Pedaling and directional control are very erratic and unstable as the individual learns the interaction of balance with the speed of the bicycle and controlling movement through space. At the point where the individual understands how the parameters of speed, balance, and directional control interact, the behavioral state (independent bicycle riding) becomes stable. The system must cross a critical point, where the speed of the bicycle makes balance easier for the behavior to become less variable in its new state.”
The authors also point out that stability in function implies depth of variability. This variability may be reflected in kinematics, centre of pressure (of the foot) movement, and centre of mass displacements. This is something we should consider when developing training and rehabilitation programs for people..
“If we consider fundamental motor skills (ie, gait, posture) and not the skills of an elite athlete, we are all skillful in our ability to walk through crowds or on diverse and challenging terrains. Therefore, it seems that variability does not decrease when we develop and refine a stable behavioral state but actually increases.”
Variability in function is a mechanism for survival.
“Variability is inherent in biological systems because it ensures survival.” More adaptive organisms tend to survive over ones less so.
In skill acquisition we see an initial high variability, reduction and then increase…
“For example, a study of coordination variability in jumpers revealed a U-shaped curve in the progression of variability. Initial high variability occurs as different strategies are attempted. Subsequently, the learner moves toward a reduction in variability as he or she performs more successfully. Then, surprisingly, as the learner becomes an expert, the variability increases again.”
Variability tends to reduce in function (e.g. gait) as we age…“aging may result in less certainty of the neuromuscular system in selecting a stable gait.” Therefore, structuring new motor learning by engaging the person in novel ways of doing regular tasks (e.g. walking with different foot strike patterns) may develop variability in the system and ‘reverse’ age associated declines in stability and balance…?
My suggestion here is simplistic, the article goes into much more detail about linear vs non-linear measures of variability and how whilst some aspects increase others decrease…worth a read.