THERAPY-Magazin
What keeps us balanced?
Explore how motor skills, sensory input, and cognitive processes interact to maintain balance and postural control. Learn why stability is vital in daily life and how it’s affected by environment, dual tasks, and neurological conditions.
Martin Huber
Freelancers in outpatient physiotherapy for neurological patients
patients
"Balance" is the ability to activate muscles to a suitable degree and with appropriate timing
Control of balance is one of man’s most fascinating abilities. The "balance system" is responsible for keeping the centre of gravity within the base of support (known as postural stability, see below) and maintaining the appropriate positioning of body parts in relation to the rest of the body and to the environment (postural orientation, see below) [4]. Some authors describe "balance" as the ability to activate muscles to a suitable degree and with appropriate timing so as to prevent a fall [19]. Almost all human movements involve these requirements to varying degrees [6]. Balance control is therefore an inherent part of most everyday activities.
When standing and walking, one of the greatest challenges is to shift and move the relatively high centre of gravity over the relatively small base of support (feet) in a controlled manner.
Limitations in our ability to balance have far-reaching consequences. Balance control correlates with independence, quality of life and self-efficacy [14,20].
Almost all neurological conditions have an impact on balance. That is why the training and improvement of balance are central goals in motor neurorehabilitation.
When standing and walking, one of the greatest challenges is to shift and move the relatively high centre of gravity over the relatively small base of support (feet) in a controlled manner.
Limitations in our ability to balance have far-reaching consequences. Balance control correlates with independence, quality of life and self-efficacy [14,20].
Almost all neurological conditions have an impact on balance. That is why the training and improvement of balance are central goals in motor neurorehabilitation.
Postural control means to carry out "an action to maintain, attain or regain balance in any posture or activity"
Mixed messages? Balance, equilibrium or postural control?
Literature in the field usually uses the term "postural control" (PC). However, the terms "equilibrium" and "balance" are often used synonymously (and have been in this article as well). Balance is defined as the "ability of a person not to fall" [12]. Postural control goes far beyond this, meaning to carry out "an action to maintain, attain or regain balance in any posture or activity" [12]. According to Horak and Macpherson, two basic factors are key: postural stability (active stabilisation of the body’s centre of gravity over the base of support by coordinating sensorimotor strategies) and postural orientation (often also referred to as postural alignment, i.e. actively maintaining the appropriate positioning of body parts in relation to the rest of the body and to the environment) [3,8].
Literature in the field usually uses the term "postural control" (PC). However, the terms "equilibrium" and "balance" are often used synonymously (and have been in this article as well). Balance is defined as the "ability of a person not to fall" [12]. Postural control goes far beyond this, meaning to carry out "an action to maintain, attain or regain balance in any posture or activity" [12]. According to Horak and Macpherson, two basic factors are key: postural stability (active stabilisation of the body’s centre of gravity over the base of support by coordinating sensorimotor strategies) and postural orientation (often also referred to as postural alignment, i.e. actively maintaining the appropriate positioning of body parts in relation to the rest of the body and to the environment) [3,8].
Capturing complexity – Interaction between many parts
In order to be able to systematically map and analyse the complexity of postural control, many well-known researchers propose using a framework [4, 9, 15, 17, 18]. One of the most widely used framework models in the field is Shumway-Cook / Woollacott [5]. This will be referred to below.
In order to be able to systematically map and analyse the complexity of postural control, many well-known researchers propose using a framework [4, 9, 15, 17, 18]. One of the most widely used framework models in the field is Shumway-Cook / Woollacott [5]. This will be referred to below.
The motor aspects include the following parts [5]: [5]:
- Active upright standing against gravity
- Appropriate positioning of body parts in relation to the rest of the body and the environment
- Active control of the body’s centre of gravity over the base of support by coordinating sensorimotor strategies (postural synergies) with internal and external influences
- Active upright standing against gravity
- Appropriate positioning of body parts in relation to the rest of the body and the environment
- Active control of the body’s centre of gravity over the base of support by coordinating sensorimotor strategies (postural synergies) with internal and external influences
Interaction model – Different control mechanisms and task requirements
According to Shumway-Cook & Woollacott, postural control is the result of the interaction of the individual (person who is moving), the task (activity) being performed and the environment in which the activity takes place [17]. We will use the term "interaction model" below.
Three basic aspects are required from the individual: motor skills (action), sensory function (perception) and cognition. We will focus mainly on three types of postural synergies: the ankle and hip joint strategies and protective responses (walking or supporting). They are necessary both for anticipatory and reactive postural control [17]. The anticipatory adjustments are also referred to as "anticipatory postural adjustments" (APAs) [11]. They allow for postural adjustments before performing a focal movement, e.g. lifting an arm while standing (internal influence). The limb movement sets the centre of gravity in motion. This "disturbance" is calculated in advance and the appropriate muscles are activated to ensure postural control.
A functioning ankle strategy is crucial for this to work. It defines the space in which the centre of gravity can be shifted while maintaining control with an upright posture (alignment). This potential movement space is called the "cone of stability" [16]. It defines the limits of stability when standing. All activities when standing (arm movements, weight transfers, etc.) take place in this movement space. The bigger it is, the better the balance.
The response to external, unpredictable influences is also important. In these situations, for example, the implementation of a fast protective step is very important (reactive postural control) [10].
According to Shumway-Cook & Woollacott, postural control is the result of the interaction of the individual (person who is moving), the task (activity) being performed and the environment in which the activity takes place [17]. We will use the term "interaction model" below.
Three basic aspects are required from the individual: motor skills (action), sensory function (perception) and cognition. We will focus mainly on three types of postural synergies: the ankle and hip joint strategies and protective responses (walking or supporting). They are necessary both for anticipatory and reactive postural control [17]. The anticipatory adjustments are also referred to as "anticipatory postural adjustments" (APAs) [11]. They allow for postural adjustments before performing a focal movement, e.g. lifting an arm while standing (internal influence). The limb movement sets the centre of gravity in motion. This "disturbance" is calculated in advance and the appropriate muscles are activated to ensure postural control.
A functioning ankle strategy is crucial for this to work. It defines the space in which the centre of gravity can be shifted while maintaining control with an upright posture (alignment). This potential movement space is called the "cone of stability" [16]. It defines the limits of stability when standing. All activities when standing (arm movements, weight transfers, etc.) take place in this movement space. The bigger it is, the better the balance.
The response to external, unpredictable influences is also important. In these situations, for example, the implementation of a fast protective step is very important (reactive postural control) [10].
The sensory aspects include the following parts [5]:
- Integration of sensory input from different information sources: Vision, balance organs and somatosensory (proprioception and surface sensitivity).
- Sensory weighting (depending on the situation, the CNS weights the sensory input differently. In a dark room, for example, the somatosensory input has to be given greater weighting than the visual input)
- Body schema (internal representation of the body)
- Integration of sensory input from different information sources: Vision, balance organs and somatosensory (proprioception and surface sensitivity).
- Sensory weighting (depending on the situation, the CNS weights the sensory input differently. In a dark room, for example, the somatosensory input has to be given greater weighting than the visual input)
- Body schema (internal representation of the body)
The cognitive aspects include the following parts [5]:
- Dual or multiple task capability: In everyday life, we are required to adapt to a constantly changing environment [15]. To do so, we need to divide our attention. Part of our attention "stays" with the PC, another part is focused on the environment.
- Self-efficacy: Feeling capable of exercising control over actions makes us feel self-effective. The degree of self-efficacy we feel determines how we behave and how we assess situations and handle them [7].
- Dual or multiple task capability: In everyday life, we are required to adapt to a constantly changing environment [15]. To do so, we need to divide our attention. Part of our attention "stays" with the PC, another part is focused on the environment.
- Self-efficacy: Feeling capable of exercising control over actions makes us feel self-effective. The degree of self-efficacy we feel determines how we behave and how we assess situations and handle them [7].
Environmental and task-related influences
Since movements always take place in an environment, this aspect also significantly influences postural control. From a therapeutic point of view, the challenge is to assess which environmental factors are relevant and therefore to be given special consideration. For instance, the type of floor has a big impact on postural control. Different requirements arise when, for example, the floor is unstable or stable, flat or sloping, slippery or solid, etc. Distractions (other people), the use of aids (stick, walking frame) or lighting conditions can also have an impact.
The task can be structured in terms of postural control according to the following criteria: steady state (static), dynamic-anticipatory and dynamic-reactive [17]. These are known as "balance mechanisms". They can be used to indicate the very basic "nature" of the (balance) task. Other relevant aspects of the task include use of the upper limbs, change of position (turning while standing, standing up/sitting down), different types of walking including tasks that often lead to balance difficulties or even falls, such as the transition from sitting to standing, turning, walking [1,2,13].
Since movements always take place in an environment, this aspect also significantly influences postural control. From a therapeutic point of view, the challenge is to assess which environmental factors are relevant and therefore to be given special consideration. For instance, the type of floor has a big impact on postural control. Different requirements arise when, for example, the floor is unstable or stable, flat or sloping, slippery or solid, etc. Distractions (other people), the use of aids (stick, walking frame) or lighting conditions can also have an impact.
The task can be structured in terms of postural control according to the following criteria: steady state (static), dynamic-anticipatory and dynamic-reactive [17]. These are known as "balance mechanisms". They can be used to indicate the very basic "nature" of the (balance) task. Other relevant aspects of the task include use of the upper limbs, change of position (turning while standing, standing up/sitting down), different types of walking including tasks that often lead to balance difficulties or even falls, such as the transition from sitting to standing, turning, walking [1,2,13].
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Therapy & Practice
THERAPY 2018-I
THERAPY Magazine
Martin Huber
Freelancers in outpatient physiotherapy for neurological patients
patients
Martin Huber is a physiotherapist who earned his Master of Science in Neurorehabilitation in 2007. As a therapist, he primarily treats patients with central nervous system disorders. Since 2010, he has been working freelance in outpatient physiotherapy for neurological patients. Several years ago, he published articles in renowned professional journals on postural control and task-oriented therapy, and he has been a speaker at various national physiotherapy congresses.
References:
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