The digit ratio (2D:4D) relationship with testosterone is moderated by physical training: Evidence of prenatal organizational influences on activational patterns of adult testosterone in physically-active women

Abstract

Background: The 2nd to 4th digit ratio (2D:4D) is regarded as a sexually dimorphic trait governed by prenatal testosterone (T) and estradiol exposure. However, relationships between the 2D:4D and adult sex hormone concentrations are inconsistent in females. Environmental contingencies (e.g., physical training) may provide a stronger basis for establishing these linkages, particularly if the relationships are plastic and not fixed. Aims: To investigate associations between 2D:4D, training hours and salivary T (sal-T) measures in physically-active women. Study design: Descriptive and quasi-experimental monitoring across the follicular (day 7), ovulatory (day 14) and luteal (day 21) phases of three menstrual cycles. Subjects: 35 naturally-cycling women training regularly for sport (range 3–12 h a week). Outcome measures: Morning sal-T concentrations and changes in sal-T to a physical and psychological stimulus (~10 min) were measured. Results: Both 2D:4D and training hours were related to morning sal-T concentrations in all three menstrual phases (p < 0.01) and their interaction was significant during ovulation. Follow-up testing revealed a negative 2D:4D and sal-T association in women reporting high, but not low, training hours each week. Participant 2D:4D was also related to sal-T changes under physical and/or psychological challenge across each menstrual phase (p < 0.01), whereas training hours and its interaction with 2D:4D were not significant predictors of these outcomes. Conclusions: 2D:4D linkages with basal and challenge-induced sal-T changes were identified in women undertaking regular physical training. Training hours also moderated the 2D:4D link to morning sal-T, but with some menstrual-phase dependency. These complexities and environmental relationships may help reconcile conflicting results.