To our knowledge these are the first population-based estimates of the prevalence of specific motor impairments in the Australian population. Unlike most previous population-based studies of motor impairment this study estimates the prevalence of multiple motor impairments. We estimate that, in residents of New South Wales aged 55 and over, the prevalence of specific impairments is as follows: weakness 12%, fatigue 9%, contracture 8%, impaired balance 4% and impaired coordination 4%. The prevalence of having at least one of these impairments is 21%. In the population aged 85 and over, the prevalence of at least one of these impairments is 42%. In comparison, the three most prevalent global diseases (Level 3 Global Burden of Diseases, Injuries, and Risk Factors Study causes) are oral disorders, headache disorders and latent tuberculosis infection, with estimated global prevalences (across all ages and all countries) in 2017 of 46, 40 and 26% respectively (calculated from reference [1] assuming a global population of 7.511 billion in 2017 [21]).
Two clear patterns emerge from the data. First, women consistently experience more difficulty using their hands, arms or legs and have more motor impairments than men. This was particularly evident for difficulty using hands, and for weakness and fatigue. Second, there was a large increase with age in difficulty using hands, arms or legs and in the prevalence of all motor impairments. There was at least twice the prevalence of all motor impairments in the group aged 85+ compared to the group aged 55–64. The prevalence of poor balance in the group aged 85+ was more than seven times that in the group aged 55–64.
Our estimates of the population prevalence of specific motor impairments are generally comparable to or lower than previous estimates. For example, it has been estimated that the population prevalence of weakness is 4–18% at 60–69 years, 9–34% at 70–79 years, and 26–68% at 80+ years [7, 9], and 5–31% at 60+ years [5, 8]. Estimates for fatigue are 38% at 18–45 years [11], 12% at 18+ years [12] and 22% at 19–80 years [10]. Estimates for impaired balance or coordination are 8–14% at 60–69 years, 16–17% at 70–79 years, and 39–46% at 80+ years [14, 15], 16% at 60+ years [13] and 28% at 65+ years [16]. Other studies have also report that women have higher prevalences of impairment [22] and that prevalence of weakness and impaired balance increase markedly with age [7, 9, 14, 15].
One explanation for the moderate variation in reported prevalences is that there were differences in case definitions across studies. Most previous studies of the population prevalence of weakness have defined cases as people with grip strength less than a specific threshold. In those studies grip strength was measured objectively. In the present study, cases or their surrogates self-reported that they had difficulty using their hands, arms or legs to carry out everyday activities because of weakness. While this approach relies on subjective self-reports, it explicitly assesses the weakness of all appendicular muscles (though it does not assess weakness of axial muscles). Previous studies of the population prevalence of specific motor impairments have not explicitly required that the motor impairment limits motor ability, although many studies have demonstrated associations between fatigue and motor ability (e.g., [23]). Studies of the prevalence of fatigue have used definitions of fatigue that reflect both the physical and the emotional or perceptual dimensions of fatigue. Interestingly, a population-based study that explicitly measured different dimensions of fatigue found similar distributions of physical and mental fatigue [22]. The present study asked participants if their “muscles tire easily” causing “difficulty using your hands, arms or legs to carry out everyday activities”. This wording emphasises the physical dimension of fatigue. Several population-based studies have quantified balance impairment using the Short Physical Performance Battery. One study conducted in the USA that used case definitions similar to those used here found that 28% of participants aged 65+ reported “problems with balance or coordination” whereas 4% of our population aged 55+ reported difficulty using hands, arms or legs to carry out everyday activities because of poor coordination and 4% reported poor balance.
The current study has several limitations. First, motor impairments were self-reported or reported by a surrogate. Self- or surrogate-reported presence or absence of a motor impairment may not always correspond with the judgement of a trained observer. This is likely to be particularly problematic for the estimates of contracture because it is likely many respondents including some who had contractures did not clearly understand what was meant by this term. Second, the survey provided data on the prevalence of motor impairments that respondents perceived “caused difficulty using the limbs”. It is likely that the level of “difficulty” experienced by respondents varied from mild to severe. A third limitation is that the response rate was low. Responses were obtained from 36% of the cohort who were invited to provide follow-up data in 2018, and the cohort consisted of the 18% who responded to the initial survey between 2006 and 2009. Thus the data provide potentially biased estimates of prevalence. It was possible to significantly reduce the potential for bias because the sample was obtained from a well-defined and well-characterised population, enabling tight calibration using the known three-way distribution of age, sex and geographical area (224 cells). Nonetheless, there may still be substantial bias if factors other than age, sex and geographical location were strongly associated with both response frequency and the prevalence of motor impairment but not with age, sex or geographical area [24].
This study shows that the prevalence of five specific motor impairments is high in New South Wales residents aged 55 and over. These impairments probably mediate geriatric syndromes [25] that are major causes of morbidity in older populations. Historically, epidemiologists have focused on quantifying the prevalence of diseases and, to a lesser extent, on the prevalence of injuries, risk factors for disease (such as high blood pressure) and non-motor impairments (such as blindness). To the extent that highly prevalent motor impairments share common mechanisms, have similar consequences and respond to the same interventions there may be merit in considering motor impairment as a significant public health problem in its own right.
