Muscle Strength and Power in People With Parkinson Disease: A Systematic Review and Meta-analysis.

Background and purpose: No studies have synthesized the literature regarding mechanical muscle function (ie, strength, power, rate of force development [RFD]) in people with Parkinson disease (PD). Here, we aimed to expand our understanding of mechanical muscle function in people with PD (PwPD) by systematically reviewing (1) the psychometric properties of isokinetic/isometric dynamometry in PD, (2) the literature comparing mechanical muscle function in PwPD with healthy controls (HC), and (3) reported associations between muscle mechanical muscle function and functional capacity and/or disease severity.

Methods: Systematic literature search in 6 databases. Included studies had to (1) enroll and report data on PwPD, (2) include assessment(s) of psychometric properties (ie, validity, reliability, responsiveness) of isokinetic/isometric dynamometry in PD, and/or (3) assess mechanical muscle function in both PwPD and HC using isokinetic/isometric dynamometry.

Results: A total of 40 studies were included. Aim 1 studies (n = 2) showed high reliability for isometric dynamometry (hip-abductor/dorsiflexor/trunk flexor-extensor/handgrip: intraclass correlations coefficients range = 0.92-0.98). Aim 2 studies (n = 40) showed impaired mechanical muscle function (ie, strength, power, RFD) in PwPD compared with HC (effect sizes range = 0.52-1.89). Aim 3 studies (n = 11) showed weak-to-strong associations between overall and lower extremities muscle strength and functional capacity and/or disease severity outcomes (ie, Unified Parkinson Disease Rating Scale).

Discussion and conclusions: Sparse methodological evidence suggests high reliability when using dynamometry in PwPD. Muscle strength, power, and RFD are impaired in PwPD compared with HC. Muscle strength is associated with functional capacity and disease severity.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A403 ).