Impact of Potential Moderating Factors on Absolute Test-Retest Reliability of Grip Strength Measurements in Healthy Populations: A Systematic Review with Meta-Analysis.

Grip strength, a biomarker, can be measured at any age; however, its values vary daily for each individual, which impacts the assessment. Absolute test-retest reliability (i.e., minimal difference, MD) is commonly defined as the variation in absolute values of measurements taken by a single person or instrument on the same item under identical conditions. Nevertheless, the potential moderators of absolute repeatability in grip strength measurements have not yet been fully elucidated. We conducted a systematic review with meta-analysis to examine the influence of potential moderating factors on the absolute test-retest repeatability of grip strength measurements in healthy populations. PubMed, Scopus, and SPORTDiscus databases were searched up to January 2025 following the PRISMA guidelines, and 48 studies were included in this review. Age, test-retest interval, and device were used as potential moderating factors; however, sex and sports experience were excluded due to the limited number of published articles. We found considerable variation among studies reporting MD and percentage of MD to measured value (%MD) across each age group. The mean MD (%MD) values were 1.9 kg (25.4%) in young children (<7 years old), 2.5 kg (13.8%) in children (7-10 years old), 4.2 kg (17.1%) in adolescents (10-18 years old), 4.0 kg (11.6%) in young adults (18-35 years old), and 4.7 kg (16.7%) in older adults (>60 years old). Neither age [effect size [ES]: 0.015 (95% confidence interval [CI]: -0.004, 0.035; p = 0.113) for MD and ES: -0.025 (95% CI: -0.089, 0.039; p = 0.439) for %MD], test-retest interval [ES: 0.006 (95% CI: -0.002, 0.013; p = 0.143) for MD and ES: 0.022 (95% CI: -0.001, 0.046; p = 0.065) for %MD] nor handgrip device (p = 0.752 for MD and p = 0.334 for %MD) served as significant moderators of MD and %MD reliability. Due to the limited number of studies, sex and sports experience were excluded from the analysis; as a result, their impacts remain unknown.