What is Balance?
- Pedro de Jesus Mendes
- May 7, 2021
- 7 min read
Updated: Feb 18
1. Balance is often taken for granted
Having intact balance control is essential for maintaining postural stability and ensuring safe mobility during daily activities, such as weight shifting, changing position while performing manual tasks, walking, or climbing stairs (Mancini & Horak, 2010). When balance is impaired, even simple actions, like walking across a gravel driveway, transitioning from sidewalk to grass, or getting out of bed in the middle of the night, can become extremely fatiguing and sometimes dangerous. In addition to unsteadiness, individuals may experience dizziness, vertigo, hearing or visual difficulties, and problems with concentration and memory.
Patients with balance disorders face a higher risk of falls, which leads to reduced activity levels and restrictions in participation in everyday life. Over time, this can result in social isolation, physical inactivity, and associated negative health consequences (Kwakkel et al., 2023; Nonnekes et al., 2018). For these reasons, it is vital to recognise and accurately assess disorders of balance and posture in clinical settings.
2. What is balance?
Balance is the ability to maintain the body’s center of mass over its base of support. A well‑functioning balance system enables individuals to see clearly while moving, sense their orientation relative to gravity, determine the direction and speed of motion, and make automatic postural adjustments to remain stable across diverse conditions and activities.
This capability is achieved and maintained through a complex sensorimotor control network that integrates sensory inputs from vision (visual cues), proprioception (information about joint position and movement), and the vestibular system (detection of linear and angular head acceleration, perception of verticality, and spatial orientation). These inputs are centrally processed, interpreted, and transformed into coordinated motor outputs that stabilize gaze and activate postural muscles. In essence, balance control emerges from the integration and coordination of multiple body systems: the vestibular and visual systems for gaze stabilization, and the sensory–motor systems for postural stabilization (Mancini & Horak, 2010).
Injury, disease, medication effects, or the natural ageing process can disrupt one or more components of this network, compromising balance. Beyond sensory and motor impairments, psychological factors—such as anxiety or fear of falling—may also negatively influence postural control.
3. Sensory input
Maintaining balance depends on sensory information that the brain receives from three key peripheral systems: the visual system, the proprioceptive system (muscles and joints), and the vestibular organs (Figure 2). Each of these systems gathers information through specialized sensory receptors, which convert visual, mechanical, and motion-related stimuli into nerve signals that are transmitted to the brain for interpretation.
4. Input from the eyes
The sensory receptors in the retina—rods and cones—play distinct roles in visual perception. Rods are more sensitive in low‑light conditions, supporting vision at night or in dim environments. Cones, on the other hand, allow us to perceive color and fine visual details. When light reaches these receptors, they convert it into neural signals that provide the brain with information about our surroundings and our position within them.
For example, as someone walks along a city street, the buildings remain vertically oriented in the visual field, while each storefront sequentially enters and exits peripheral vision. These visual cues help the brain interpret spatial orientation and movement relative to the environment.
5. Input from the muscles and joints
Proprioceptive information from the skin, muscles, and joints is gathered by sensory receptors that detect stretch and pressure within surrounding tissues. For instance, when a person standing upright leans forward, pressure increases on the front portion of the soles of the feet, and these receptors immediately signal the change to the brain. With any movement of the legs, arms, or other body segments, the receptors respond by sending continuous streams of neural impulses.
Together with other sensory inputs, these stretch‑ and pressure‑based cues allow the brain to determine the body's position in space and the relationship between different body segments. Signals from the neck and ankles are particularly important: proprioceptive input from the neck informs the brain about the direction in which the head is turned, while input from the ankles reflects body sway and movement relative to the support surface—including its characteristics, such as being firm, soft, slippery, or uneven.
6. Input from the vestibular system
The vestibular apparatus provides sensory information about linear and angular head acceleration, perception of verticality, and spatial orientation. Each ear contains three semicircular canals, the utricle, and the saccule. The utricle and saccule detect gravity and head position relative to vertical, as well as linear acceleration. The semicircular canals, arranged roughly at right angles to one another, are filled with endolymph and respond to rotational movements of the head.
When the head rotates in the plane of a particular canal, the endolymph lags behind due to inertia, creating pressure against the canal’s sensory receptor. This mechanical deflection triggers neural impulses that inform the brain about movement in the plane of that specific canal. When both vestibular systems are functioning normally, the organs on the left and right sides send symmetrical signals to the brain when the head is still.
7. Integration of sensory input
Balance information gathered by the peripheral sensory organs—the eyes, proprioceptive receptors in muscles and joints, and the vestibular organs in the inner ear—is transmitted to the brainstem. There, these signals are organised and integrated with learned information from the cerebellum (the brain’s coordination center) and the cerebral cortex (responsible for cognition and memory).
The cerebellum contributes knowledge about automatic, well-practised movements that have been refined through repetition. For example, a tennis player who practices serving repeatedly learns to optimise postural control during that action. The cerebral cortex adds higher‑level, experience‑based information. For instance, knowing that icy sidewalks are slippery prompts a person to adjust their movement strategy to walk safely under those conditions (see Figure 3).
8. Processing of conflicting sensory input
A person can become disoriented when sensory information from the eyes, proprioceptive system, and vestibular organs does not match. For example, this can happen when someone is standing on the sidewalk next to a bus that begins to pull away. The large moving vehicle creates a strong visual cue that may give the pedestrian the illusion of moving, even though they are actually standing still. Meanwhile, proprioceptive feedback from muscles and joints, along with vestibular signals from the inner ear, indicate that the body has not changed position.
In such situations, vestibular input can help resolve the sensory conflict by providing reliable information about head and body motion. In addition, higher-level cognitive processes—such as memory and reasoning—may prompt the person to look down at the pavement to visually confirm that their body is stationary, helping restore a correct sense of orientation.
9. Motor output
As sensory information is integrated, the brainstem sends coordinated signals to the muscles that control movement of the eyes, head, neck, trunk, and legs. These motor commands allow a person to maintain postural stability while also keeping vision clear during movement.
10. Motor output to the muscles and joints
A baby learns to maintain balance through repeated practice, as sensory signals travel from receptors to the brainstem and then out to the muscles, gradually establishing efficient neural pathways. With repetition, these pathways become easier and faster for the impulses to travel—a process known as facilitation. As this process strengthens over time, the child becomes increasingly capable of maintaining balance during a wide range of activities. Strong evidence indicates that such synaptic reorganisation continues throughout life as individuals adapt to new or changing movement environments.
This principle of pathway facilitation explains why dancers and athletes train so intensively: even highly complex movements become almost automatic after sufficient repetition. It also means that if one sensory input becomes impaired, the balance system can reorganise and adapt through practice, allowing the individual to regain a sense of stability using the remaining sensory information.
11. Motor output to the eyes
The vestibular system sends motor control signals to the eye muscles through an automatic mechanism known as the vestibulo‑ocular reflex (VOR). When the head is still, the vestibular organs on both sides of the head generate an equal number of neural impulses. When the head turns to the right, the right vestibular organs increase their firing rate, while the left side decreases it.
This difference in neural activity between the two sides drives compensatory eye movements that stabilise gaze. As a result, the eyes remain fixed on a target during active head movements—such as running or watching a fast‑paced sports match—as well as during passive movements, like when sitting in a car that accelerates or decelerates.
12. The coordinated balance system
The human balance system relies on an intricate network of sensorimotor control mechanisms working in constant communication. These interdependent feedback loops can be disrupted when any component is affected by injury, disease, or the ageing process. When balance is impaired, individuals may experience additional symptoms such as dizziness, vertigo, visual disturbances, nausea, fatigue, and difficulties with concentration.
The complexity of this multisensory system presents significant challenges in diagnosing and treating the root cause of imbalance. Because the vestibular, visual, and proprioceptive systems must work together seamlessly, dysfunction in any one of them can markedly disturb a person’s sense of stability. Vestibular disorders, in particular, pose a unique challenge due to the vestibular system’s close interaction with cognitive processes and its crucial role in controlling eye movements and posture.
You may also like to check: 12 Protocols for Balance Assessment with force/pressure plate.
Sources:
1- Vestibular Disorders Association: The Human Balance System— A Complex Coordination of Central and Peripheral Systems
2- National Institute on Deafness and Other Communication Disorders (NIDCD)- Balance Disorders
3- Modelação Numérica do índice de Tinetti e de Berg; 2012; Universidade de Coimbra;
Kwakkel, G., Stinear, C., Essers, B., Munoz-Novoa, M., Branscheidt, M., Cabanas-Valdés, R., Lakičević, S., Lampropoulou, S., Luft, A. R., Marque, P., Moore, S. A., Solomon, J. M., Swinnen, E., Turolla, A., Alt Murphy, M., & Verheyden, G. (2023). Motor rehabilitation after stroke: European Stroke Organisation (ESO) consensus-based definition and guiding framework. European Stroke Journal, 23969873231191304. https://doi.org/10.1177/23969873231191304
Mancini, M., & Horak, F. B. (2010). The relevance of clinical balance assessment tools to differentiate balance deficits. European Journal of Physical and Rehabilitation Medicine, 46(2), 239–248.
Nonnekes, J., Goselink, R. J. M., Růžička, E., Fasano, A., Nutt, J. G., & Bloem, B. R. (2018). Neurological disorders of gait, balance and posture: A sign-based approach. Nature Reviews Neurology, 14(3), 183–189. https://doi.org/10.1038/nrneurol.2017.178
Pedro de Jesus Mendes
Sensing Future Technologies
pedromendes@sensingfuture.pt