Why are people with dementia especially likely to fall? Weak legs and poor balance are certainly causes, but the real key is often overlooked. The chance of a person with dementia falling is far higher than that of an older person of the same age with normal cognition, mainly because of a mechanism directly linked to cognition, the "dual-task gait difficulty" of losing balance when walking and thinking at the same time. Fall prevention goes in the wrong direction unless this point is understood.
In other words, patients often do not fall while standing still. They fall at the moment of walking while attending to something else (such as listening to someone speak, avoiding clutter or thinking about the destination). Each of the following is covered below: why fall risk goes up, what dual-task gait difficulty is and why it is dangerous, and whether a change in gait is an early sign of cognitive decline.
How dementia relates to fall risk
The chance of an older person with dementia falling is clearly higher than that of people of the same age with normal cognition, and weak muscles or degenerating joints alone do not explain it. What really raises the risk is several factors acting together: weaker judgement that leads the person to underestimate hazards in the environment, difficulty paying attention to several things at once, slower reactions to changes around the person, and drowsiness caused by some medicines. All these sources point to brain function and not simply to weak legs.
Fortunately, there are things that can be done. A systematic review and pooled analysis found that exercise programmes designed for community-dwelling older people with dementia can reduce fall risk by about 32%(Burton 2015). However, the quality of the programme is vital. Another randomised controlled trial found that if exercise intensity is too low and supervision is insufficient, it not only fails to help prevent falls but may make older people fall more, because they are more active (Taylor 2021). This shows that fall prevention exercise must be of enough intensity and have professional supervision, and it does not work just by "moving around more". For how to practise safely at home, see the specific approach in the article on fall prevention exercise specific to dementia.
What dual-task gait difficulty is
Walking looks like something done without thinking, but it uses a lot of brain power. To keep a steady step length, rhythm and balance, the brain must keep using executive function and attention to monitor the whole body. When cognitive function is normal, the brain has plenty of reserve, and a person can chat on the phone while walking with ease. With dementia, the reserve of brain capacity falls and things are quite different.
When a patient has to walk and deal with something else at the same time (for example talking, counting or avoiding obstacles), this is what research calls a dual task. The brain's resources then cannot cover both, and the gait shows changes visible to the eye: walking speed falls suddenly, the steps shorten, sway from side to side increases, and some people even stop walking without realising. Clinically this is known as "stops walking when talking". The phenomenon is in itself a very practical warning sign of fall risk.
Once the mechanism behind this is clear, it is plain that fall prevention cannot rest on practising balance in static standing alone, because everyday falls often happen at the moment of "moving and thinking at the same time". Multimodal exercise that combines aerobic, strength and balance work is better than resistance training alone at improving walking speed, mobility and balance performance (Blankevoort 2010). If dual-task elements can be added in moderation and safely, it comes closer to what everyday life needs. For an objective look at whether exercise can improve only physical function or also help cognitive ability, and how far the evidence has got, see the article on the evidence for exercise in dementia. To lay a foundation for balance and fall prevention first, the general principles of training are in the cross-topic article on balance and fall prevention exercise.
Why practising static balance alone is not enough
- When standing still, the brain has enough resources to keep the body balanced
- Falls usually happen in a moment of walking, turning or being distracted
- Fall prevention training must imitate these real everyday situations as far as possible
Dual-task training needs supervision by a professional
- For high-risk patients, handling thinking tasks while walking carries a certain risk
- This kind of training must be assessed by the therapist first and then added step by step in a safe environment
- Never push yourself to try it alone at home
Slower walking speed and cognitive decline
Does an older person walking more slowly and unsteadily mean the brain has started to decline? It may, but it cannot be decided from walking speed alone. Several longitudinal studies have observed that slower walking speed (especially a large slowing under dual-task conditions) sometimes appears before cognitive decline or at the same time as it, and people like this have a relatively higher risk of cognitive decline and falls later on. Gait control and cognitive function share the same set of brain networks to some extent, so when one gets worse, the other cannot be ignored either.
But this should not be over-read. There are very many reasons for slowing walking speed, such as knee pain, medication side effects, failing eyesight or reduced heart and lung function, all of which slow a person's steps and may have nothing to do with cognitive function. The more appropriate approach is to treat a clearly slower walking speed, or abnormal gait under dual-task conditions, as a warning sign to get a formal assessment, and not to decide alone that the person has dementia. In Hong Kong, anyone with a suspicion can first be referred by the family doctor to the geriatrics department or a memory clinic of the Hospital Authority. In the community, they can also call the Hong Kong Alzheimer's Disease Association (香港認知障礙症協會) (hotline 2338 1120) to ask about assessment and support services.
On home assessments we often see an older person who stands very steadily when still, but whose steps fall into disorder at once when asked to answer a question while walking. This is what dual-task gait difficulty looks like. It also explains why family members who feel the older person looks fine in general are surprised by a sudden fall. Only an assessment in the real home setting where the person moves around can find these hidden fall hazards.
When a physiotherapist should step in
If a family member with dementia shows any of the following, professional help should be considered: has fallen or nearly fallen, sways clearly when walking or needs to hold on to furniture along the way, loses balance with only a little distraction, or has recently slowed down markedly. Rather than waiting until a fall breaks a bone, it is better to assess early and begin training. Nova Health's registered physiotherapists provide home physiotherapy, assessing the patient's gait, balance and dual-task performance on the spot, designing graded and safe fall prevention exercise according to the person's cognition and mobility, and giving advice on improving the home environment, so that training really fits what daily living needs.