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

Relative age in Brazilian swimmers and para swimmers

abstract This study aimed to analyze the relationships between swimming competitive events, functional classification and relative age and to detect if the relative age affects performance in Brazilian swimmers and para swimmers. Data were retrieved from public databases and birth dates were classified in four quartiles (Q1 = January-March; Q2 = April-June; Q3 = July-September; Q4 = October-December). Descriptive statistics, Chi-square tests and ANOVA were used. The 50 m freestyle is the competitive event with 2349 swimmers, followed by 100 m (n = 1817) and 200 m freestyle (n = 905), and 200 m butterfly with 42 swimmers. Para swimmers are mainly distributed to S14, S6 and S5 functional classes (n = 140, 87 and 45), and individual medley events were less represented at SM3, SM9 and SM11 (n = 1 swimmer). Most of swimming events (86.36%) and para swimming functional classes (51.43%) are represented by swimmers and para swimmers born in the first and second quartiles. Moderate associations between functional classification and relative age were observed (p < 0.0001, Cramer’s V = 0.277). No effects of relative age on swimmers and para swimmers’ performance were noticed (p > 0.05). The great functional class seems to be related to great para swimmers’ relative age. Quartiles distribution shows the advantage of being born in the first months of the year to be registered among the most talented Brazilian swimmers and para swimmers.

Vitamin D supplementation and gross motor development: A 3-year follow-up of a randomized trial

BACKGROUND

Vitamin D status during pregnancy, early childhood and season-at-birth are implicated in gross motor development (GMD).

AIM

To test whether vitamin D intake in infancy and season-at-birth affect GMD in early childhood.

STUDY DESIGN

3-year follow up study of a single-center trial.

SUBJECTS

Healthy infants (n = 116) were allocated to 400 (standard-of-care), 800 or 1200 IU/day of vitamin D3 supplementation from 1 to 12 months; n = 70 returned for follow-up at 3-years.

OUTCOME MEASURES

The main outcome was GMD using the Peabody Developmental Motor Scales-2 which includes gross motor quotient (GMQ) and stationary, locomotion and object manipulation subtests.

RESULTS

GMQ scores were normal (≥85) in 94 %. An interaction between dosage group and season-at-birth (p = 0.01) was observed for GMQ and stationary standardized score; among winter/spring born children, the 1200 IU/d scored higher vs. 400 and 800 IU/d groups. Object manipulation standardized score was higher (p = 0.04) in children in the 1200 vs. 400 IU/d group, without interaction with season-at-birth.

CONCLUSIONS

GMD in young children who received 400 IU/d of supplemental vitamin D in infancy is not influenced by season-at-birth. This dose of vitamin D of 400 IU/d as recommended in North America adequately supports GMD. The modest enhancement in GMD with 1200 IU/d in winter/spring born children requires further study.

Birth month and mortality in Japan: a population-based prospective cohort study

Epidemiologic studies investigating the association between birth season and risk of mortality in adulthood are limited and have yielded inconclusive results. We aimed to examine the relationship between birth month and all-cause and cause-specific mortality, after controlling for potential confounders, including lifestyle and medical factors, in a population-based cohort study in Japan. We included 28,884 subjects (13,262 men and 15,622 women) from Takayama City, aged 35 years or older without cancer, stroke, and ischemic heart disease, who were born in Japan at baseline. Participants who were enrolled in 1992 were followed up for over 16 years. Information including place of birth, lifestyles, and medical history was obtained from a baseline questionnaire. We performed a Cox proportional hazards analysis to determine the association between birth month and all-cause and cause-specific mortality after adjusting for potential confounders. During the follow-up period (mean follow-up: 14.1 years), 5,303 deaths (2,881 men and 2,422 women) were identified. After controlling for multiple covariates, it was found that being born in April or June was associated with an increased risk of all-cause mortality compared to being born in January (hazard ratio [HR] 1.138; 95% confidence interval [CI], 1.006-1.288 and HR 1.169; 95% CI, 1.028-1.329, respectively). The HRs for cardiovascular mortality were significantly higher in participants born in March and May (HR 1.285; 95% CI, 1.056-1.565 and HR 1.293; 95% CI, 1.040-1.608, respectively). Our findings indicate that an individual's birth month may be an indicator of the susceptibility to mortality in later life.

Relative Age Effects as Evidence of Selection Bias in Major League Baseball Draftees (2013-2018)

ABSTRACT

Herring, CH, Beyer, KS, and Fukuda, DH. Relative age effects as evidence of selection bias in major league baseball draftees (2013-2018). J Strength Cond Res 35(3): 644-651, 2021-The purpose of this study was to examine if relative age effects (RAEs) or the unequal birth-date distribution among a cohort group of individuals exist in Major League Baseball (MLB) draftees. This study comprised 7,078 men drafted in the MLB first-year player draft from 2013 to 2018. Data collected for each draftee included birth date, year drafted, academic-level classification, position, round drafted, batting side, and throwing arm. Draftee's birth dates were categorized into quarters based on the calendar year for baseball in the United States (Q1: August-October; Q2: November-January; Q3: February-April; Q4: May-July). Player birth-date distributions were compared with average expected birth-date distributions and evaluated with the χ2 goodness of fit statistic. Significant χ2 tests were followed up by calculating the standardized residual for each quarter. Differences from the expected frequencies were found for the overall group (p < 0.001) with standardized residuals for baseball athletes born in Q1 (z = +4.45) and Q3 (z = -4.15) exceeding ±2.0. Similar patterns were noted for high schoolers (Q1: z = +3.30; Q3: z = -3.28), pitchers (Q1: z = +2.78; Q3: z = -3.12), early middle rounders (Q1: z = +3.08; Q3: z = -2.67), late rounders (Q1: z = +2.70; Q3: z = -2.61), right-side hitters (Q1: z = +3.23; Q3: z = -2.26), left-handed pitchers (Q1: z = + 2.12; Q3: z = -2.59), and right-handed positional players (Q1: z = +3.12; Q3: z = -2.12). Consistent with the majority of previous research, RAEs are apparent in MLB draftees, with specific patterns of unequal distribution among subsets of athletes.

The relative age effect on physical fitness in preschool children

The aim of the present study was to investigate the existence of a relative age effect (RAE) on physical fitness of preschoolers. Anthropometry and physical fitness were assessed in 3147 children (3-5 years old) using the PREFIT battery. Based on the birth year, participants were divided into 3year groups (3-, 4- and 5-years). Within each year group, 4quarter groups were created: quarter 1, preschoolers born from January to March; quarter 2, from April to June; quarter 3, from July to September; quarter 4, from October to December. The MANCOVA analysis revealed a main effect of year group (Wilks' λ = 0.383; F_10,5996 = 369.64; p < 0.001, η_p ² = 0.381) and of quarter (Wilks' λ = 0.874; F_15,8276.6 = 27.67; p < 0.001; η_p ² = 0.044) over the whole battery of tests. To the best of our knowledge, this is the first study to report the existence of RAE at the preschool stage. In general, performance improved as the relative age increased (i.e., those born in quarter 1 performed better than those in the other quarters). Individualization strategies should be addressed within the same academic year not only in elementary or secondary years but also in preschoolers.

National Strength and Conditioning Association Position Statement on Long-Term Athletic Development

There has recently been a growing interest in long-term athletic development for youth. Because of their unique physical, psychological, and social differences, children and adolescents should engage in appropriately prescribed exercise programs that promote physical development to prevent injury and enhance fitness behaviors that can be retained later in life. Irrespective of whether a child is involved in organized sport or engages in recreational physical activity, there remains a need to adopt a structured, logical, and evidence-based approach to the long-term development of athleticism. This is of particular importance considering the alarmingly high number of youth who fail to meet global physical activity recommendations and consequently present with negative health profiles. However, appropriate exercise prescription is also crucial for those young athletes who are physically underprepared and at risk of overuse injury because of high volumes of competition and an absence of preparatory conditioning. Whether the child accumulates insufficient or excessive amounts of exercise, or falls somewhere between these opposing ends of the spectrum, it is generally accepted that the young bodies of modern day youth are often ill-prepared to tolerate the rigors of sports or physical activity. All youth should engage in regular physical activity and thus should be viewed as "athletes" and afforded the opportunity to enhance athleticism in an individualized, holistic, and child-centered manner. Because of emerging interest in long-term athletic development, an authorship team was tasked on behalf of the National Strength and Conditioning Association (NSCA) to critically synthesize existing literature and current practices within the field and to compose a relevant position statement. This document was subsequently reviewed and formally ratified by the NSCA Board of Directors. A list of 10 pillars of successful long-term athletic development are presented, which summarize the key recommendations detailed within the position statement. With these pillars in place, it is believed that the NSCA can (a) help foster a more unified and holistic approach to long-term athletic development, (b) promote the benefits of a lifetime of healthy physical activity, and