The Relationship Between Digit Ratio (2D:4D) And Muscular Fitness: A Systematic Review And Meta-Analysis

Background: Digit ratio (2D:4D), a marker of prenatal testosterone exposure, is a weak negative correlate of sports/athletic/fitness performance. While numerous studies have examined the relationship between 2D:4D and physical fitness, there has never been a comprehensive study that has synthesized studies examining relationships between 2D:4D and muscular fitness. Objectives: To systematically review and meta-analyze the relationship between 2D:4D and muscular fitness measured as handgrip strength (HGS). Methods: This study systematically searched five electronic databases, reference lists, topical systematic reviews/meta-analyses, and personal libraries in November 2020. Peer-reviewed, cross-sectional studies that reported Pearson’s correlation coefficients between objectively measured 2D:4D and HGS were included. This study used random-effects meta-analysis to estimate the pooled correlation and the 95% confidence interval (95%CI), and moderator analyses to estimate the influence of sex and age. Results: Data from 22 studies, representing 5271 individuals from 11 countries ranging in (mean) age from 10.4 to 58.0 years, were included. Overall, there was a weak negative correlation between 2D:4D and HGS (r = –0.15, 95%CI =–0.20 to –0.09), indicating that individuals with low 2D:4Ds had high HGS. There was substantial heterogeneity found between studies (Q = 123.4, p \u3c0.0001; I2 = 74%), but neither sex (Q = 0.003, p = 0.96) nor age (Q = 0.46, p = 0.50) significantly moderated the pooled correlation. Conclusions: This study found a weak negative relationship between 2D:4D and HGS, which showed substantial heterogeneity between studies, but was neither moderated by sex nor age. This finding probably reflects both the long-term (organizational) and short-term (activational) benefits of testosterone