Factors Affecting Reliability of Grip Strength Measurements in Middle Aged and Older Adults

<ns4:p> <ns4:bold>Background:</ns4:bold> Grip strength is a well-established marker of frailty and a good predictor of mortality that has been measured in a diverse range of samples including many population studies. The reliability of grip strength measurement in longitudinal studies is not well understood. </ns4:p> <ns4:p> <ns4:bold>Methods:</ns4:bold> Participants (n=130) completed a baseline and repeat health assessment in the Irish Longitudinal Study on Ageing. Grip strength was assessed using dominant and non-dominant hands (two trials on each). Repeat assessments were conducted 1-4 months later and participants were randomised into groups so that 50% changed time (morning or afternoon assessment) and 50% changed assessor between assessments. Intra-class correlation (ICC) and minimum detectable change (MDC <ns4:sub>95</ns4:sub> ) were calculated and the effects of repeat assessment, time of day and assessor were determined. </ns4:p> <ns4:p> <ns4:bold>Results:</ns4:bold> Aggregated measures had little variation by repeat assessment or time of day; however, there was a significant effect of assessor (up to 2 kg depending on the measure used). Reliability between assessments was good (ICC>0.9) while MDC <ns4:sub>95</ns4:sub> ranged from 5.59–7.96 kg. Non-aggregated measures alone, taken on the non-dominant hand were susceptible to repeat assessment, time of day, assessor and repeated measures within-assessment effects whereas the dominant hand was only affected by assessor. </ns4:p> <ns4:p> <ns4:bold>Conclusions:</ns4:bold> Mean and maximum grip strength had a higher ICC and lower MDC <ns4:sub>95</ns4:sub> than measures on the dominant or non-dominant hands alone. The MDC <ns4:sub>95</ns4:sub> is less than 8 kg regardless of the specific measure reported. However, changing assessor further increases variability, highlighting the need for comprehensive assessor training and avoiding changes within studies where possible. </ns4:p>