Handgrip is a simple proxy for muscular strength and a clinically useful measure of muscular function. A weaker handgrip strength is associated with poorer quality of life, increased mortality, and poorer cognition—including cognitive decline—in aging populations.1-3 The neurophysiologic underpinnings of the relationship between handgrip strength and cognition are unclear. Higher total brain volume is associated with greater muscle size but not necessarily with muscle strength.4 Increased handgrip strength is associated with fewer age-related white matter hyperintensities in the brain.5 Another potential mechanism is inflammation, as both age-related cognitive decline and weaker handgrip strength are associated with higher levels of inflammatory markers.6
Whether the association between handgrip strength and cognition generalizes to other non-aging populations, including patients with psychiatric disorders, is unknown. In particular, no previous studies have investigated the association in patients with schizophrenia, which is associated with a broad range of cognitive deficits. Firth and colleagues7 used population-scale data to investigate the relationship between maximal handgrip strength and cognition (across 5 domains) in middle-age people with and without schizophrenia.
The researchers performed a cross-sectional analysis of data collected from 2007 through 2010 from the baseline assessment for the United Kingdom Biobank, a nationwide cohort study of relationships between lifestyle, environment, and genetics to health-related outcomes. Over 500,000 adults aged 37 to 73 years were recruited across 22 assessment centers throughout the UK. For the present study, patients with neurological conditions associated with impaired cognition were excluded. The United Kingdom Biobank is also integrated with hospital records, allowing researchers to stratify participants based on the presence or absence of an ICD-10 diagnosis of non-affective psychosis (F20-29). The control sample consisted of all participants without a history of non-affective psychosis.
Handgrip strength was performed using a hand dynamometer, with a single trial for each hand. The maximal score for the (self-reported) dominant hand was used in all analyses. If subjects identified themselves as ambidextrous or did not specify a dominant hand, the hand with the highest score was used. Cognition was assessed using a 15-minute computerized battery with 5 individual tasks/domains, including reaction time, reasoning, numeric memory, visuospatial memory. Each cognitive domain was analyzed using linear mixed models or generalized linear mixed models, controlling for age, sex, weight, education, and geography and testing center.
Dr. Miller is Associate Professor, Department of Psychiatry and Health Behavior, August University, August, GA.
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6. Weaver JD, Huang MH, Albert M, et al. Interleukin-6 and risk of cognitive decline: MacArthur Studies of Successful Aging. Neurology. 2002;59:371-378.
7. Firth J, Stubbs B, Vancampfort D, et al. Grip strength is associated with cognitive performance in schizophrenia and the general population: a UK Biobank study of 476559 participants. Schizophr Bull. 2018 (In press).