We know that postural control has two purposes, postural orientation and postural stability. When considering postural orientation, the focus is on the question “Where am I?” whereas postural stability the focus is on the question "Where am I going?”. However, things are not as simple and “rigid” as they sound. Maintaining balance requires us to adapt our movement responses when confronting new demands, such as when tasks and environmental conditions change. We can state that balance is a complex skill centered on the interaction of all sensorimotor processes [1].
The author, Fay Horak brilliantly categorized and explained the main resources required for postural stability and postural orientation (see image below). Understanding the contribution of each one of these systems is fundamental to getting to bottom of the true nature of balance dysfunction of each individual, allowing for the most efficient treatment planning [2].
In this article we will focus on movement strategies, particularly on how we can improve reactive movement strategies.
What are movement strategies?
Our body is not a stable body, even our internal body functions are enough to cause some instability. So, besides a normal postural tone and skeletal alignment, we need movement strategies to keep ourselves balanced. These movement strategies consist in specific movement patterns, known as the ankle strategy, the hip strategy and the stepping strategy. The first two are used to recover stability when feet are in place, the stepping strategy is used when, in order to recover stability, a new base of support is needed [1].
These strategies can be used in a feedback control mode as in response to sudden perturbations, such as a sudden acceleration on a bus ride, or a tip or slip when walking. As well as in a feedforward control mode, referring to the postural responses that happen in anticipation of a voluntary movement, such as leaning forward to pick up something heavy [1].
Perturbation-based balance training
Perturbation-based balance training, also known as reactive balance training, has been gaining a lot of attention for the past years, mainly because it has been shown in research to successfully reduce the risk of fall in older adults, people with Parkinson’s Disease and stroke. Christopher McCrum et al. [3] defined Perturbation-based balance training as “balance training that uses repeated, externally applied mechanical perturbations to trigger rapid reactions to regain postural stability in a safe and controlled environment”, importantly, these mechanical perturbations should mimic common types of perturbations felt on daily life.
1 - Important aspects to consider when using Perturbation-based balance training
-The perturbations used should:
Be difficult to predict;
Mimic daily life perturbations;
Have enough intensity to suddenly destabilize the patient;
Be easily adjustable in terms of intensity for each patient;
-Stability recovery after each perturbation should be measured to monitor each patient’s progress and adjust the treatment plan.
-Consider the appropriate safety measures.
This short video shows how to perform perturbation-based balance training with Kine-Sim. The activity chosen was a Bus ride, the disturbances created by the movement of the two force plates mimic the accelerations and decelerations felt during the bus ride shown in the screen. During this activity balance responses are recorded and measured (center of pressure velocity and center of pressure displacement).
2 - What mechanisms underlie the improvement of balance skills and fall prevention through perturbation-based balance training?
Scientific literature available on this subject suggests that the improvements observed in reactive balance are resultant from improvements in both the feedforward and feedback control modes of stability [3].
In respect to feedforward control mode, predictive adaptations use prior experience of similar perturbations to adjust the motor output, readjusting the center of mass position and/or the base of support. Improvements in proactive balance behavior leads to a reduction in the disturbance of perturbations which in consequence decreases the scale of the recovery response [3].
Regarding feedback control mode, improvements in reactive response can be resultant from: early detection of perturbation, faster response initiation, optimization of motor programs and muscle synergies [3].
3 - What is the evidence behind the use of Perturbation-based balance training in clinical populations?
There is growing evidence on the use of Perturbation-based balance training in healthy older adults, older adults with a history of falls [4], people with Parkinson’s Disease [5], stroke [6] and multiple sclerosis [7]. For people with Parkinson’s Disease, Perturbation-based balance training has shown to reduce delay in activation of postural responses, to induce more stable reactive trunk movements and to reduce center of mass displacement [8]. However, more studies are needed to investigate important questions such as the ideal training dose, including the magnitude of perturbations, number of perturbations per sessions and number of training sessions per week. In addition, some people may report fear/anxiety related to the use of perturbations, to tackle this, the perturbations used should be less intense in the beginning and gradually increase while confidence increases as well. Furthermore, the use of safety equipment such as a safety harness, should also be considered [3].
Do you have questions about this topic? Or want to know more about balance system?
Schedule a 15 minute talk with me!
Ana Souto
Meet Ana, a physiotherapist with a master's degree in human physiology, currently specializing in neurobiology. Her professional journey has led her to gain extensive expertise in both neurology and sports physiotherapy.
Ana currently serves as the clinical specialist at PhysioSensing, a cutting-edge Balance Assessment and training device. Leveraging her strong foundation in scientific research and evidence-based practices, Ana creates customized assessment and training plans. Her approach is firmly rooted in the latest scientific findings, ensuring that PhysioSensing users receive the most effective and up-to-date care.
In addition to her role in designing tailored programs, Ana plays a pivotal role in guiding new clients through the learning process of using PhysioSensing. She also provides advanced training and support to existing customers seeking to further deepen their clinical practice knowledge and stay on top of the latest scientific advancements.
References
[1] A. Shumway-Cook and M. Woollacott, Motor Control - Translating Research Into Clinical Practice, 4th ed. 2010.
[2] F. B. Horak, ‘Postural orientation and equilibrium: what do we need to know about neural control of balance to prevent falls?’, Age and Ageing, vol. 35, no. suppl_2, pp. ii7–ii11, Sep. 2006, doi: 10.1093/ageing/afl077.
[3] C. McCrum et al., ‘Perturbation-based balance training: Principles, mechanisms and implementation in clinical practice’, Front. Sports Act. Living, vol. 4, p. 1015394, Oct. 2022, doi: 10.3389/fspor.2022.1015394.
[4] K. A. Bieryla and M. L. Madigan, ‘Proof of Concept for Perturbation-Based Balance Training in Older Adults at a High Risk for Falls’, Archives of Physical Medicine and Rehabilitation, vol. 92, no. 5, pp. 841–843, May 2011, doi: 10.1016/j.apmr.2010.12.004.
[5] D. B. Coelho, C. E. N. De Oliveira, M. V. C. Guimarães, C. Ribeiro De Souza, M. L. Dos Santos, and A. C. De Lima-Pardini, ‘A systematic review on the effectiveness of perturbation-based balance training in postural control and gait in Parkinson’s disease’, Physiotherapy, vol. 116, pp. 58–71, Sep. 2022, doi: 10.1016/j.physio.2022.02.005.
[6] S. Handelzalts, M. Kenner-Furman, G. Gray, N. Soroker, G. Shani, and I. Melzer, ‘Effects of Perturbation-Based Balance Training in Subacute Persons With Stroke: A Randomized Controlled Trial’, Neurorehabil Neural Repair, vol. 33, no. 3, pp. 213–224, Mar. 2019, doi: 10.1177/1545968319829453.
[7] M. S. B. Mohamed Suhaimy, Y. Okubo, P. D. Hoang, and S. R. Lord, ‘Reactive Balance Adaptability and Retention in People With Multiple Sclerosis: A Systematic Review and Meta-Analysis’, Neurorehabil Neural Repair, vol. 34, no. 8, pp. 675–685, Aug. 2020, doi: 10.1177/1545968320929681.
[8] C. Ribeiro De Souza et al., ‘Perturbation‐based balance training leads to improved reactive postural responses in individuals with Parkinson’s disease and freezing of gait’, Eur J of Neuroscience, vol. 57, no. 12, pp. 2174–2186, Jun. 2023, doi: 10.1111/ejn.16039.
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