Int J Sports Med 2014; 35(12): 1017-1023
DOI: 10.1055/s-0034-1368725
Training & Testing
© Georg Thieme Verlag KG Stuttgart · New York

Athletic Performance and Birth Month: Is the Relative Age Effect More than just Selection Bias?

G. R. H. Sandercock
1   Centre for Sports and Exercise Science, School of Biological Sciences. University of Essex, Colchester, Essex, UK
A. A. Ogunleye
2   Center for Obesity Management, University of Alberta, Edmonton, Canada
D. A. Parry
1   Centre for Sports and Exercise Science, School of Biological Sciences. University of Essex, Colchester, Essex, UK
D. D. Cohen
3   Instituto Masira, Facultad de la Ciencias de la Salud, Universidad de Santander, Bucaramanga, ­Colombia
M. J. D. Taylor
1   Centre for Sports and Exercise Science, School of Biological Sciences. University of Essex, Colchester, Essex, UK
C. Voss
4   Centre for Hip Health and Mobilitiy, University of British Columbia, Vancouver, Canada
› Author Affiliations
Further Information

Publication History

accepted after revision 13 January 2014

Publication Date:
02 June 2014 (online)


The aim of this study was to determine if month of birth affects performance in 3 tests of physical function in children and adolescents. We measured cardiorespiratory fitness, handgrip strength and lower-body power expressed them relative to (whole year) age then compared scores between calendar year birth-months. We also expressed test performance as the likelihood of achieving criterion-referenced fitness standards. There were significant main effects of birth-month for cardiorespiratory fitness (F=4.54, p<0.001), strength (F=6.81, p<0.001) and power (F=3.67, p<0.001). Children born in November were fitter and more powerful than those born at other times, particularly the summer months (April, May and June). October-born children were stronger than those born in all months except September and November. This relationship was evident despite controlling for decimal age and despite no significant inter-month differences in anthropometric characteristics.

There is a clear physical advantage for those born in the autumn and this may explain some of the bias in sports selection attributed to the relative age effect, particularly when the British school-year (September) cut-off is used.

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