When an older adult becomes unsteady, one of the first recommendations they may hear is:
“You need stronger legs.”
Strength matters, but balance is more complex than strength alone. A person can have reasonably strong legs and still have difficulty recovering after a trip. Another person may have some weakness but remain stable because their sensation, reactions and movement strategies are working well.
At Clinics GRP, we increasingly think about balance through a concept called Sensorimotor Reserve. It helps explain why two people of the same age can have very different balance abilities — and why preventing falls requires more than simply strengthening muscles.
Key points
- Balance depends on several systems working together, not strength alone.
- Small changes in sensation, movement, power, pain or confidence can combine to reduce a person's safety margin.
- Assessment is most useful when it identifies what happens as the task becomes more challenging.
Your brain is constantly solving a movement problem
Standing and walking may feel automatic, but the nervous system is constantly combining information from the eyes, inner ears, joints, muscles, skin and soles of the feet.
It uses that information to work out:
- where the body is and where it is moving;
- whether the surface is stable;
- how much force is required; and
- whether a corrective movement is needed.
If balance is disturbed, the system must rapidly choose whether to correct through the ankles, move through the hips, adjust the trunk, use the arms, take a step or grab something nearby. Balance therefore depends on having several possible solutions available.
Ageing can gradually reduce the number of options
Ageing does not affect every system in every person. Over time, however, smaller changes can accumulate, including:
- less sensation through the feet;
- reduced ankle movement;
- lower leg strength or muscular power;
- slower reactions;
- changes in vision or greater reliance on visual information;
- joint pain; or
- reduced confidence after a fall.
Each change may be relatively small. The difficulty often appears when several are present at the same time. This is where Sensorimotor Reserve becomes useful.
Think of reserve as the safety margin
Imagine a person has a certain amount of physical and sensorimotor capacity available. Standing in the kitchen may use only a small proportion of it, leaving plenty in reserve.
Now change the task: the person is walking outside at dusk, the ground is uneven, they are carrying shopping, their knee hurts and they turn their head to speak to somebody. The task suddenly requires much more capacity.
A person with a large reserve may barely notice the change. Someone operating closer to their limit may become unsteady. The difference may not be that one person “has balance” and the other does not; it may be the size of their remaining safety margin.
Why falls can appear unpredictable
Families sometimes say:
“Mum normally walks quite well. I don't understand why she fell.”
Sensorimotor Reserve helps explain this. A person may have enough capacity for normal walking but very little spare capacity when demands occur together.
- Lower-demand task: normal walking may be manageable.
- Higher-demand task: walking + poor lighting + uneven ground + fatigue + knee pain + distraction may exceed the available reserve.
A fall can therefore occur without the person's usual walking suddenly becoming dramatically worse. The circumstances changed, and the demand exceeded the available capacity.
Balance assessment should become more challenging
Asking someone to stand still with their feet apart does not tell us everything we need to know. A person may perform that test perfectly. The more useful question is:
What happens when the balance system is challenged?
A physiotherapist may therefore observe what happens when:
- the feet are brought closer together;
- vision is reduced or the head moves;
- the surface changes;
- the person reaches or divides their attention;
- a step must be taken quickly; or
- balance is safely disturbed.
The aim is to identify where the person's balance begins to break down. That threshold can tell us much more than an easy task.
Sensation through the feet matters
The soles of the feet provide important information about contact with the ground. If sensation changes with ageing or a condition such as peripheral neuropathy, the nervous system may receive less reliable information and rely more heavily on vision.
That strategy may work in a bright room but become less effective at night, in a dark hallway, on uneven ground or when the person needs to look elsewhere. Balance rehabilitation may therefore need to address how sensory information is being used, rather than focusing only on muscle strength.
Joint movement matters too
The body needs enough movement to use different balance strategies. The ankle, for example, helps control the body as the centre of mass moves. If ankle movement is restricted, the person may rely more on the hips, trunk or a stepping strategy.
That compensation may work well. But if hip strength, reaction time or stepping ability are also reduced, fewer options remain. Restricted movement may therefore consume reserve by removing one possible solution, even when it is not the sole cause of the balance problem.
Strength and power are not the same thing
Strength describes how much force a person can produce. Power also considers how quickly that force can be produced — an important distinction when balance is suddenly disturbed.
A person may have enough strength to rise slowly from a chair but insufficient speed of force production to recover quickly from a trip. Depending on the individual, rehabilitation may therefore include strength, power, rapid stepping, balance reactions and functional movement.
Reactive balance may be particularly important
Everyday balance is often about recovering rather than preventing every disturbance. We all trip, misjudge a step or encounter an unexpected change in the environment. The critical issue is what happens next.
Can the person take an effective recovery step, produce enough force quickly, move the foot in the right direction, arrest their momentum and regain control? When appropriate, reactive balance can be an important part of physiotherapy assessment and rehabilitation.
The aim is to build a bigger reserve
The goal is not simply to teach somebody to pass a balance test. It is to increase the capacity available beyond their everyday needs. That may involve:
- building strength and power;
- increasing useful joint movement;
- improving walking and reactive stepping;
- improving sensory use;
- reducing pain where possible;
- increasing confidence; and
- safely progressing towards more challenging tasks.
The more effective movement solutions a person has available, the more options their nervous system has when something unexpected occurs.
A better question for balance care
Our clinicians do not view balance as a single system. We look at the interaction between sensation, joint movement, strength and power, reaction, pain, vision and vestibular information, confidence and attention, and the demands of the environment.
A useful balance assessment looks beyond a simple yes/no judgement and identifies which factors are reducing the person's ability to respond.
Instead of asking only, “Is this person's balance poor?”, we ask:
What is reducing this person's ability to respond when the task becomes difficult?
Once we understand that, rehabilitation can become more targeted. The aim is not to make ageing disappear, but to help the person build enough physical and sensorimotor capacity that the demands of everyday life remain comfortably within what they can do. That is what we mean by increasing Sensorimotor Reserve.