What do these people have in common?

76-year-old grandmother with Parkinson’s disease who tripped on an uneven sidewalk, falling, and breaking her hip.
48-year-old construction worker who tripped on an electrical cord.
36-year-old office worker who just got progressive lenses on her new glasses and slipped on a wet floor.

All have been referred to rehabilitation for consequences after falling; that is where the similarities end: each person will require a different treatment approach based on the underlying reason for falling. We all must be able to anticipate a change in walking surface or recover from a slip to prevent a fall; even more so, an athlete must successfully anticipate, and respond to the environment to make a winning play. Whether your focus is on neurological, orthopedic, or sport rehabilitation, applying motor control principles is key to identifying task impairments and targeting the training program to achieve successful outcomes. Sport coaches and athletes rely on biomechanical analyses to measure performance details invisible to the eye to gain the competitive edge (force plate and motion analysis in baseball and golf are two great examples). This blog post introduces you to motor control concepts; in future blog posts, we’ll explore how you can train both automatic and voluntary components of postural control and answer how you might identify impairments and target your rehabilitation of each of these people.

What is Motor Control?

Motor control is an area of natural science that explores how the nervous system interacts with other body systems and the environment to produce purposeful, coordinated movements1. It includes perspectives from biomechanics, kinesiology, neurophysiology, neuroscience, and cognitive psychology to answer the complex question of, “How do we organize and produce movement?”.

The brain adapts its motor outputs to respond to changing sensory inputs from the body and from the external environment, ranging from day-to-day to complex sport environments. The central nervous system selects, suppresses, and combines these inputs to determine the most correct response from an abundance of solutions, all equally capable of creating the desired movement. Nikolai Bernstein, a neurophysiologist who pioneered early motor control and motor learning science, observed that there were many ways to organize movement patterns to achieve the same goal of hammering a nail: “repetition without repetition”[1].

How exactly this happens is the subject of debate and many theories, including two:

Schmidt’s Schema Theory and generalized motor programs (GMP): movement is controlled by motor programs with common characteristics that are governed by time. For example, the GMP for walking is different than that for running. Memory and the central nervous system play a key role. Rehabilitation should address central pattern generators in retraining movements in the context of functional tasks.
Dynamical Systems Theory: coordinated movement patterns self-organize based on environmental conditions, individual body and limb dynamics, and task demands. Practice and experience help the individual to solve movement problems while emphasizing physical movement characteristics.

The Continuum of Postural Motor Control

Our ability to maintain balance and perform complex motor skills occurs at several levels in the nervous system, including spinal reflex loops, central motor program generators for complex rhythmic activities like walking, subcortical structures (the basal ganglia and cerebellum), and the brain’s cortex. Automatic postural reactions occur in response to losing balance from a slip, a sudden uneven surface, or other external perturbation of the center of mass that might result in a fall. These semi-automatic, pre-programmed postural reactions can be modified with training. Multisensory inputs from the somatosensory, vestibular, and visual systems are coordinated with motor outputs to allow us to maintain balance in a variety of settings from quiet standing to executing a play during a game.

Computerized dynamic posturography (CDP) includes both automatic tests of postural reactions (motor control test (MCT) and adaptation test (ADT)) and voluntary sensorimotor tests (sensory organization test (SOT)). It is possible to measure the latency times, amplitude, and symmetry of semi-automatic postural reactions with the MCT, while the ADT measures the body’s sway energy in response to rotating, or tilting, the force platform up or down. These tests provide useful information about reflexive and semi-automatic postural reactions. The MCT helps identify impairments in the first 160 mSec of the body’s response to perturbation by detecting the rapid changes in center of pressure (CoP) occurring with active muscle forces to counteract the sudden force platform movement. We control our CoP to stay within the base of support and to keep from falling.

Humans need to be able to rapidly organize an automatic postural response to maintain balance when an unexpected force causes us to move into an unstable position; for example, missing the last step, slipping on ice, or bumping into an object. These automatic pre-programmed reactions are organized by a small number of motor programs (i.e., a stored set of instructions on how a movement sequence is to be performed) and may also be selected in anticipation of, or after, a perturbation[1,5].

Being able to respond to these sudden rapid perturbations is key to preventing falls. No amount of standing on foam, exercise balls, or one-legged standing will train the semi-automatic reactions to these events: the training must be specific to the functional demands. Immersive virtual reality (IVR) perturbation training programs solve this problem by allowing the clinician to change the perturbation types, visual and environmental context, and perceptual demands.

Motor and postural control systems are complex! Stay tuned: the next topic will explore how the MCT, ADT, and perturbation training target the long-loop semi-automatic postural responses. For an in-depth education on how to conduct centrally programmed and voluntary motor control tests, visit Bertec’s Interactive and On-Demand Education offerings.

References:

1. Latash, M. L. (2012). Fundamentals of motor control. Academic Press.

2. Magill R.A., & Anderson D.I.(Eds.), (2018). Motor control theories in Motor Learning and Control: Concepts and Applications, 11e. McGraw Hill. Available from: https://accessphysiotherapy.mhmedical.com/content.aspx?bookid=2311&sectionid=179409127

3. Petrynski, W. (2016). A scientific evening with N.A. Bernstein and R.A. Schmidt. Kinesiology. 25. 11-24. 10.5604/17310652.1226481. Available from: https://www.researchgate.net/publication/312519120_A_scientific_evening_with_NA_Bernstein_and_RA_Schmidt [accessed 11 Jan, 2023]

4. Forgaard CJ, Franks IM, Maslovat D, Chua R (2016) Perturbation Predictability Can Influence the Long-Latency Stretch Response. PLoS ONE 11(10): e0163854. https://doi.org/10.1371/journal.pone.0163854

5. Horak, F. B., & Nashner, L. M. (1986). Central programming of postural movements: adaptation to altered support-surface configurations. Journal of neurophysiology, 55(6), 1369-1381.