Could prenatal hormone levels influence surfing prowess?
The relative length of your second digit (i.e. index finger, 2D) to that of your fourth (ring finger, 4D) expressed as a fraction is known as the digit ratio or 2D:4D. This ratio has been demonstrated to correlate with performance in numerous sports research (1) and is thought to be negatively associated with testosterone, and positively to oestrogen, levels in the developing foetus (2). The relative lengths of fingers are established by the end of the 1st trimester (3) and are stable throughout childhood, puberty, and on towards adulthood. Neither are they influenced by inter-individual maturational variability (4). Therefore, the digit ratio may offer a practical anthropomorphic (i.e. physical body characteristic-derived) marker for performance in surfers.
This is exactly the premise by which Kilduff et al. (5) conducted their study in 2009. They considered the relationship of 2D:4D to performance in 46 male surfers at the 5-star Professional World Qualifying Series competition in Newquay, UK, that year. Experienced surf coaches rated the surfers in terms of overall surfing performance. These ratings were significantly correlated with one another. An overall measure of ability was obtained by calculating the mean of each rating awarded and by taking the final contest placing into account as well.
The science bit…
The mean 2D:4D was: right 0.994 (SD=0.023) and left 0.976 (0.028), the difference was significant. The right 2D:4D (but not left or right–left 2D:4D) was significantly negatively correlated with coaches’ ratings (rS=0.58, r2=0.34, p=0.0001) and the competition result (rS=0.30, r2=0.09, p<0.05) but was not significantly related to either left or right–left 2D:4D. Nor was right 2D:4D significantly related to age, height, or surfing experience.
The surfers’ mass was also negatively correlated with performance (i.e. lighter surfers tended to rate higher), but the observed effect size was moderate (rS=0.32, r2=0.09, p=0.03). Even after removing for mass effect, the right digit ratio was found to remain significantly negatively correlated with surfing performance (rS=0.51, r2=0.26, p=0.0001).
The researchers concluded that, as observed in other sports, an apparent low right 2D:4D (i.e. high prenatal testosterone and low oestrogen) correlated with high surﬁng ability in male.
So what’s the practical application?
Potentially, coaches may employ 2D:4D as an additional tool to talent select when screening young surfers to further develop to a high standard.
- Honekopp J, Schuster M. A meta-analysis on 2D:4D and athletic prowess: Substantial relationships but neither hand out-predicts the other. Pers Individ Diff 1: 4–10, 2010.
- Manning JT, Scutt D, Wilson J, and Lewis-Jones DI. The ratio of 2nd to 4th digit length: A predictor of sperm numbers and levels of testosterone, LH and oestrogen. Hum Reprod 13: 3000–3004, 1998.
- Malas MA, Dogan S, Evcil EH, Desdicioglu K. Fetal development of the hands, digits and digit ratio (2D:4D). Early Hum Dev 82: 469–475, 2006.
- Trivers R, Manning JT, Jacobson A. A longitudinal study of digit ratio (2D:4D) and other ﬁnger ratios in Jamaican children. Horm Behav 49: 150–156, 2005.
- Kilduff LP, Cook CJ, Manning JT. Digit ratio (2D:4D) and performance in male surfers. JStrengthCondRes 25(11): 3175–3180, 2011.
SD=Standard Deviation; rS=Spearman rank correlation coefficient; r2=Coefficient of determination
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