The Relationship Between Digit Ratio (2D:4D) and Aspects of Cardiorespiratory Fitness: A Systematic Review and Meta-Analysis

Introduction

Digit ratio (2D:4D), a proxy of prenatal testosterone exposure, is a putative marker of physical fitness. No study has comprehensively synthesized studies examining associations between 2D:4D and cardiorespiratory fitness (CRF). We aimed to systematically review and meta-analyze studies reporting associations between 2D:4D and aspects of CRF.

Methods

We systematically searched the literature for full text, refereed, cross-sectional studies reporting Pearson's correlation coefficients between objectively measured 2D:4D and at least one aspect of CRF. CRF was objectively assessed using field-based measures (maximal long-duration exercise performance) or laboratory-based measures (maximal oxygen uptake [VO_2max], ventilatory threshold [VT], or mechanical efficiency [ME]). We used random-effects meta-analysis to estimate the pooled correlation and 95% confidence interval (95% CI) for aspects of CRF, and moderator analyses to estimate the influence of sex and age.

Results

Data from 22 studies, representing 5293 individuals (54% male; mean age range = 10.1–40.2 years) from 12 countries were included. We found a significant strong negative correlation for VT (r = −0.61, 95% CI = −0.78, −0.37) and a significant weak negative correlation for exercise performance (r = −0.18, 95% CI = −0.25, −0.10), indicating that individuals with lower 2D:4Ds had higher VT and better exercise performance. No significant correlations were found for VO_2max or ME. Neither sex nor age were significant moderators, except for age which moderated the correlation for exercise performance.

Conclusions

2D:4D is a proxy for some aspects of CRF like exercise tolerance (i.e., VT) and performance, but not other aspects like aerobic capacity and efficiency.