Handgrip is a simple proxy for muscular strength and a clinically useful measure of muscular function. What are the neurophysiologic underpinnings of the relationship between handgrip strength and cognition?
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.
A total of 476,559 participants met the study criteria and had measurements of handgrip strength and at least one cognitive domain; 1162 participants with schizophrenia were included in the cohort.
The mean age was 54 for patients with schizophrenia and 57 for controls. Just over half (54%) of the patients and 45% of controls were male. More than 95% of the participants (patients with schizophrenia and controls) completed both the visual memory and reaction time tasks, but fewer than 40% of the participants in both groups completed the other tasks. Handgrip strength was lower in both men and women with schizophrenia compared with controls. In the control and/or “general population” sample, higher handgrip strength was significantly positively associated with better performance on visual memory, reaction time, reasoning, number memory, and prospective memory tasks (P < .001 for each).
In patients with schizophrenia, higher handgrip strength was a significant positive predictor of better visual memory and reaction time (P < .001 for each) and predicted prospective memory at the trend level (P = .078). The magnitude of these associations was similar in patients with schizophrenia and in controls. In a post-hoc analysis, the pattern of findings was unchanged when considering only participants aged 55 years or younger, and after controlling for waist circumference and past history of cardiovascular disease
This was the first study of handgrip strength and cognition in patients with schizophrenia, and the largest general population sample of this association to date, particularly in middle-aged adults. A limitation of the study is that fewer participants in the schizophrenia sample completed all of the cognitive tasks, which may have impacted on statistical power.
The bottom line
Handgrip strength is correlated with cognition in both schizophrenia and the general population. Further research is needed regarding the direction and mechanism(s) of these associations, towards novel approaches for the assessment (and even potentially the treatment of) cognitive impairment in patients with schizophrenia.
For the slideshow, see Get a Grip: Strength and Cognition in Schizophrenia.
Dr. Miller is Associate Professor, Department of Psychiatry and Health Behavior, August University, August, GA.
1. Sayer AA, Syddall HE, Martin HJ, et al. Is grip strength associated with health-related quality of life? Findings from the Hertfordshie Cohort study. Age Ageing. 2006;35:409-415.
2. Leong DP, Teo KK, Rangarajan S, et al. Prognostic value of grip strength: findings from the Prospective Urban Rural Epidemiology (PURE) study. Lancet. 2015;386:266-273.
3. Fritz NE, McCarthy CJ, Adamo DE. Handgrip strength as a means of monitoring progression of cognitive decline: a scoping reviewer. Ageing Res Rev. 2017;35:112-123.
4. Kilgour AH, Todd OM, Starr JM. A systematic review of the evidence that brain structure is related to muscle structure and their relationship to brain and muscle function in humans over the lifecourse. BMC Geriatr. 2014;14:85.
5. Viscogliosi G, Di Bernardo MG, Ettorre E, et al. Handgrip strength predicts longitudinal changes in clock drawing test performance. An observational study in a sample of older non-demented adults. J Nutr Health Aging. 2017;21:593-596.
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).