Exploratory Evidence of Sex-Dimorphic Associations of the Ulna-to-Fibula Ratio, a Potential Marker of Pubertal Sex Steroid Exposure, with the Implicit Need for Power

Abstract

Abstract Objectives We propose a novel marker of pubertal organizing hormone effects on the brain, long bone length, and assess its relationships to implicit motives, especially the implicit need for power (nPower). Methods In a partly exploratory approach, we tested 126 participants (after exclusions; 53 men, 73 women), in a cross-sectional design using the Picture-Story Exercise (nPower, activity inhibition), standard anthropometric measurements (BMI, height), and calipers to assess bone length of the ulna and fibula. Results Results indicated that a sex-dimorphic (d = 0.55) Ulna-to-Fibula Ratio (UFR), which is independent of body height, best captures the variance in our data. While we did not find bivariate relationships between long bone length and nPower, a sex-dimorphic interaction of nPower and activity inhibition on UFR-asymmetry (UFRr-l; right versus left UFR) emerged. High UFRr-l scores were related to the inhibited power motive (high nPower, high activity inhibition) in men, while for women the pattern was (non-significantly) reversed. In addition, UFR was predicted by a sex-dimorphic effect of nPower, with low UFR scores being associated with a higher nPower in men and a tendency for high UFR scores being related to lower nPower in women. Conclusions We discuss our results regarding UFR’s potential as a sex-dimorphic marker of the organizing effects of pubertal steroid hormones on the motivational brain beyond hand and face parameters routinely used in current research. Finally, we examine how our findings fit recent results obtained for the relationship between 2D:4D digit ratio or facial width-to-height ratio and nPower.