Background: Weakness is reported in Parkinson's but always unadjusted for recognized factors that influence muscle strength such as participants' age, gender, and body size. This may obscure the true association of Parkinson's with muscle strength.
Objective: To evaluate the relationship between grip strength, Parkinson's severity, and duration adjusting for these factors.
Methods: Age, gender, height, weight, grip strength, Unified Parkinson's Disease Rating Score (UPDRS) motor score, Hoehn and Yahr (H&Y) stage, disease duration, number of comorbidities and medications, Barthel score, Mini Mental State Examination (MMSE) score, and Malnutrition Universal Screening Tool (MUST) score were recorded.
Results: Fifty-seven of 79 (72%) people with Parkinson's resident in one town were recruited. Age, gender, height, and Parkinson's severity were the most significant determinants of grip strength. Each unit increase in UPDRS motor score and H&Y stage was associated with lower grip strength in univariate linear regression analyses adjusted for gender: -0.3 kg strength (95% confidence interval = -0.51, -0.09), P = .006 for each additional UPDRS point, and -3.87 kg strength (95% confidence interval = -6.54, -1.21), P = .005 for each additional H&Y stage. Disease duration was not associated with grip strength. In multivariate regression, Parkinson's severity remained strongly associated with grip strength (UPDRS score P = .09; H&Y stage P = .04).
Conclusions: This is the first demonstration that increasing severity of Parkinson's was associated with weaker grip after adjustment for known influences on muscle strength. Participants' age, gender, and body size also had a significant impact on strength. Adjustment of reported values for all these factors is essential to allow accurate reporting of grip strength values in intervention trials and comparison between different groups.
Keywords: Parkinson’s; grip strength; muscle strength; weakness.
© The Author(s) 2015.