How tired an activity makes someone predicted their falls better than asking about fatigue

Design

prospective cohort with monthly structured telephone fall ascertainment, generalised estimating equations

Population

223 community-dwelling adults aged 60 and over (109 with multiple sclerosis, 114 controls), September 2019 to April 2025

Primary outcome

prospectively recorded falls

Effect

physical fatigability OR 1.54 (95% CI 1.25-1.91), mental fatigability OR 1.41 (1.12-1.77); physical fatigability 1.37 (1.09-1.71) after accounting for group status

Fatigue is reported by most older people and predicts very little. Fatigability is different: it asks how tired a specified activity of a specified duration would make you, which anchors the answer to something concrete. This prospective cohort applied the Pittsburgh Fatigability Scale at baseline to 223 community-dwelling adults aged 60 and over - 109 with multiple sclerosis and 114 healthy controls - then tracked falls by structured monthly telephone interview from September 2019 to April 2025.

After adjustment for demographic and clinical covariates including previous falls, higher physical fatigability predicted falls (odds ratio 1.54, 95% CI 1.25-1.91, P<0.001), as did mental fatigability (1.41, 1.12-1.77, P=0.004). Physical fatigability remained significant after accounting for whether the participant had multiple sclerosis (1.37, 1.09-1.71, P=0.006); mental fatigability attenuated. Having multiple sclerosis did not modify the relationship - the association was the same in both groups.

That last point is what makes this usable beyond a neurology clinic. The scale takes two minutes, needs no equipment, and adds information beyond the strongest predictor we already use, which is a history of previous falls. It is a prospective association, not a demonstration that reducing fatigability reduces falls, and 223 participants from one cohort is modest. But as a question to add to a falls assessment - how tired would a 30-minute walk make you - it costs nothing and points at something potentially modifiable.

• Add a fatigability question to the falls assessment: how tired would a specified activity of a specified duration make you
• Do not substitute it for a falls history - the association held after adjusting for previous falls, meaning it adds rather than replaces
• Treat high physical fatigability as a prompt to assess gait, strength and exercise capacity rather than as a diagnosis
• Note the association was the same with and without multiple sclerosis, so this is not a neurological finding
• Remember this is prospective association only - no trial has shown that treating fatigability prevents falls

Why it matters

It offers a two-minute question that adds to the one predictor we already trust, and points at something that might be trainable.

Don't overread it

A prospective observational association - it does not show that improving fatigability reduces falls.

The statistics, in plain English

An odds ratio of 1.54 is per unit of the fatigability scale, so the effect across the full range of scores is considerably larger than the number suggests. That physical fatigability survived adjustment for previous falls is the important methodological point - previous falls is the strongest single predictor available, and a variable that adds information on top of it is doing real work. With 223 participants, the confidence intervals are wide enough that the size of the effect is uncertain even though its direction is not.

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