Digit ratio (2D:4D) and physical fitness (Eurofit test battery) in school children

The Relationship Between Digit Ratio (2D:4D) and Aspects of Cardiorespiratory Fitness: A Systematic Review and Meta-Analysis

INTRODUCTION

Digit ratio (2D:4D), a proxy of prenatal testosterone exposure, is a putative marker of physical fitness. No study has comprehensively synthesized studies examining associations between 2D:4D and cardiorespiratory fitness (CRF). We aimed to systematically review and meta-analyze studies reporting associations between 2D:4D and aspects of CRF.

METHODS

We systematically searched the literature for full text, refereed, cross-sectional studies reporting Pearson's correlation coefficients between objectively measured 2D:4D and at least one aspect of CRF. CRF was objectively assessed using field-based measures (maximal long-duration exercise performance) or laboratory-based measures (maximal oxygen uptake [VO2max], ventilatory threshold [VT], or mechanical efficiency [ME]). We used random-effects meta-analysis to estimate the pooled correlation and 95% confidence interval (95% CI) for aspects of CRF, and moderator analyses to estimate the influence of sex and age.

RESULTS

Data from 22 studies, representing 5293 individuals (54% male; mean age range = 10.1-40.2 years) from 12 countries were included. We found a significant strong negative correlation for VT (r = -0.61, 95% CI = -0.78, -0.37) and a significant weak negative correlation for exercise performance (r = -0.18, 95% CI = -0.25, -0.10), indicating that individuals with lower 2D:4Ds had higher VT and better exercise performance. No significant correlations were found for VO2max or ME. Neither sex nor age were significant moderators, except for age which moderated the correlation for exercise performance.

CONCLUSIONS

2D:4D is a proxy for some aspects of CRF like exercise tolerance (i.e., VT) and performance, but not other aspects like aerobic capacity and efficiency.

Potential Predictor of Epigenetic Age Acceleration in Men: 2D:4D Finger Pattern

OBJECTIVES

Second to fourth digit ratio is widely known indicator of prenatal sex hormones proportion. Higher prenatal androgenization results in longer fourth finger and lower 2D:4D index. The aim of this study was to determine whether the 2D:4D digit ratio is associated with DNA methylation (DNAm) age dependently on sex.

MATERIAL AND METHODS

The study included 182 adults (106 females and 76 males) with a mean age of 51.5 ± 13 years. The investigation consisted of three main parts: a survey, anthropometric dimensions measurements (fingers length) and methylome analysis using collected blood samples. Genome-wide methylation was analyzed using EPIC microarray technology. Epigenetic age and epigenetic age acceleration were calculated using several widely applied algorithms.

RESULTS

Males with the female left hand pattern had more accelerated epigenetic age than those with the male pattern as calculated with PhenoAge and DNAmTL clocks.

CONCLUSIONS

Finger female pattern 2D:4D above or equal to 1 in males is associated with epigenetic age acceleration, indicating that prenatal exposure to estrogens in males may be related to aging process in the later ontogenesis.

An Association Between Left-Hand Digit Ratio (2D:4D) and Anthropometric Indexes in Chinese Children and Adolescents Aged 8-15 Years in Bengbu City

OBJECTIVES

The digit ratio (2D:4D) is a possible marker of prenatal hormone exposure. The purpose of this study was to explore the relationships between digit ratio (2D:4D) and anthropometric indexes in Chinese children and adolescents.

METHODS

This study is a cross-sectional study. A school-based survey among 685 children and adolescents aged 8-15 years were conducted by stratified cluster sampling. The length of index finger (2D) and ring finger (4D) of the left hand, height, sitting height (ST), weight, chest circumference (CC), waist circumference (WC), hip circumference (HC), and abdominal skinfold thickness (AST) were measured. Pearson correlation and multivariate linear regression were used to analyze associations between 2D:4D and above indexes.

RESULTS

In girls, 2D:4D was positively related to WC, AST, waist-to-height (WHtR), waist-to-hip ratio (WHR) after adjusting for ages (p < 0.05). The WC, AST, WHtR, and WHR among girls with 2D:4D ≥ 1 were significantly higher than those among girls with 2D:4D < 1, respectively (p < 0.05). However, there was no correlations between digit ratio (2D:4D) and above anthropometric indexes in boys (p > 0.05).

CONCLUSIONS

The 2D:4D was related to anthropometric indexes in girls, which suggests that the maternal prenatal hormone exposure might be related to the anthropometric indexes of their female offspring.

Associations between Agility, the Relative Age Effect, Siblings, and Digit Ratio (D2:D4) in Children and Adolescents

BACKGROUND

This study aims to analyze the influence of relative age effects, siblings, and digit ratio on the agility of children and adolescents.

METHODS

The study included 283 children (9.54 ± 1.36 years) and 296 adolescents (14.68 ± 1.36 years) from four different schools. The analyzed variables included anthropometric data, the presence of siblings, relative age effect, and results from the 10 × 5 m shuttle run test.

RESULTS

The findings indicated no significant association between agility and either the 2D:4D ratio or the relative age effect in both children and adolescents (p > 0.05). Additionally, having siblings did not have a notable impact on agility. Multiple regression analysis confirmed that relative age did not influence this lack of association (quarter of birth: p = 0.345, β = 0.039; siblings: p = 0.100, β = -0.069). However, boys showed higher performance than girls in the 10 × 5 m shuttle run test, and higher body mass index was related to lower agility.

CONCLUSIONS

These findings contribute to existing knowledge on the relative effects of age and provide valuable information for physical education teachers on the influence of the 2D:4D ratio and the presence of siblings on the physical fitness of children and adolescents.

Evaluation of digit ratio (2D:4D) in breast cancer patients

Breast cancer is a hormone-dependent cancer. Hormonal exposure begins in the intrauterine period and continues in later years of life. 2D:4D ratio is accepted as an indicator of this exposure. The aim of this study was to investigate whether there is a difference in 2D:4D ratio between pathological subgroups of breast cancer and healthy control group. In this study, 204 participants, 154 breast cancer patients and 50 healthy control volunteers with similar age distribution, were included. Both hands of all participants were scanned using a digital scanner. The second and fourth finger lengths were measured using a digital measuring ruler with an accuracy of 0.05 mm. The 2D:4D ratio was calculated as the length of the second finger divided by the length of the fourth finger. A total of 204 patients (55 triple negative, 52 luminal B, 33 luminal A, 14 HER2-overexpessing and 50 healthy control volunteers) were subjected to finger scanning. There was no statistically significant difference in mean age between the groups. The right hand 2D:4D ratio was significantly lower in the Luminal A group compared to the other groups (p < 0.048). Although prenatal hormonal exposure is accepted as a risk factor for breast cancer, no study has evaluated patients in pathological subgroups. The 2D:4D ratio may be associated with breast cancer especially in the luminal A group in which hormone receptors are strongly positive and which has a better prognosis compared to the other groups.

Prenatal androgenization (2D:4D) predictions of tennis match-play success in junior players: A search for physiological explanations

AIM

This study aims to investigate the possible association between digit ratio (2D:4D) and match-play success (MPS) in junior tennis players. In addition, we consider the possible explanatory pathways of these associations in relation to psychological, strength, power, and hormonal parameters.

METHODS

We performed a cross-sectional study, with a sample comprised of 64 male junior tennis players (11-18 years old). Digit ratio was calculated from direct finger measurements. In addition, we measured the ratio of wins by number of matches played in 5 years of official competition (MPS), handgrip strength (HGS), standing long jump (SLJ), training (in weekly hours), and expertise (number of years in official competition). Salivary testosterone and cortisol levels were measured before and after physical "challenge" tests.

RESULTS

The 2D:4D correlated negatively with HGS and SLJ. MPS was also negatively associated with 2D:4D, but was positively correlated to HGS, expertise, training, and self-confidence (SC). Multiple linear regression showed 2D:4D and expertise were associated with MPS (43%-54%). None of the physical, or hormonal variables tested explained the links between 2D:4D and MPS.

CONCLUSION

Therefore, the specific fitness components influenced by prenatal androgenization that moderate sports success remain unknown. Future studies should explore the interaction of 2D:4D, with tennis exercises as a challenge to induce hormonal change, the effect of pubertal stage, and the influence of aerobic endurance in determining MPS.

Jumping Rope Improves the Physical Fitness of Preadolescents Aged 10-12 Years: A Meta-Analysis

To systematically review the effects of jumping rope on physical fitness among 10 to 12-year-old preadolescents, and to provide evidence-based support for its use in school physical education curriculum work. The PubMed, Web of Science, SPORTDiscus, ScienceDirect, and CNKI databases were searched for randomized controlled trials that assessed jumping rope and physical fitness among preadolescents aged 10-12 years. Meta-analyses were used to calculate the standardized mean difference (SMD) values and 95% confidence intervals (CI), and subgroup analyses were conducted on intervention duration, frequency and period. A total of 1048 subjects from 15 studies were included. Compared to regular physical education courses, jumping rope did not show a significant advantage in terms of body morphology. In terms of physical function, boys showed greater improvements in vital capacity, and girls showed greater improvements in resting HR. In terms of physical performance, boys showed greater improvements in speed, upper-body strength, lower-body strength, muscular endurance and agility, while girls showed greater improvements in coordination and balance. Boys experienced a minimal improvement in flexibility, while girls did not show a significant difference. Combining the results of the subgroup analyses, the optimal session time, frequency and intervention length of jumping rope for significantly improving the physical fitness of preadolescents were >40 min, 2 times/week and 8-12 weeks, respectively. In conclusion, jumping rope provides small to large benefits over regular physical education for both boys and girls aged 10-12 years in terms of physical function and physical performance indicators other than flexibility, while showing no significant advantage in terms of body morphology. Based on the available research, it is recommended that children aged 10-12 years participate in jump rope sessions for at least 40 minutes once or twice a week for 8-12 weeks to better develop physical fitness.

Determinants of handgrip strength at age 2 years in children born moderate and late preterm and associations with neurodevelopmental outcomes

BACKGROUND

Handgrip strength (HGS) indicates current and future health. Although preterm infants have an increased risk of poor grip strength in later life, its determinants and relationship with neurodevelopment are not well understood.

AIMS

To determine HGS in children born preterm and explore the relationship of HGS with demography, anthropometry, nutritional factors, and neurodevelopmental outcomes.

STUDY DESIGN

A prospective cohort study of moderate-late preterm babies enrolled in a randomised trial of nutritional support strategies, the DIAMOND trial.

SUBJECTS

A total of 116 children born between 32 and 35 weeks' gestation, whose HGS was measured at 2 years' corrected age.

OUTCOME MEASURES

HGS was measured using a dynamometer, and neurodevelopment was assessed using the Bayley Scales of Infant Development-III. Anthropometry and body composition were assessed at birth, discharge, and at 4 months' and 2 years' corrected age. Information on demographics and breastfeeding practices, including type of milk at discharge and duration of exclusive breastfeeding, was collected using questionnaires.

RESULTS

The mean (standard deviation) HGS was 2.26 (1.07) kg. The Bayley scores were < 85 (-1 standard deviation) in 6 %, 20 %, and 1 % for the cognitive, language, and motor scales, respectively. Multiple regression analysis revealed that HGS was positively associated with language and motor scores (p < .05) after adjusting for confounding factors. HGS was not associated with sex, anthropometry, body composition, or breastfeeding practices. Maternal education was independently associated with HGS (p < .01).

CONCLUSIONS

HGS at age 2 years in children born moderate-late preterm is associated with language and motor development and maternal education level.

The digit ratio (2D:4D) and testosterone co-predict vertical jump performance in athletic boys: Evidence of organizational and activational effects of testosterone on physical fitness

The digit ratio (2D:4D) is a negative correlate of boy's physical fitness, and thought to arise from organizational effects of prenatal testosterone on different bodily systems. During human ontogeny, activational effects of testosterone on body size and strength offers another pathway to physical fitness. We tested these hypotheses by examining the organizational and activational effects of testosterone on vertical jump performance in athletic boys. Using a cross-sectional design, 173 boys (aged 9 to 18 years) were tested for standing height, body mass, body fat, fat-free mass, weekly training activity, training history, salivary testosterone and cortisol, R2D:4D, L2D:4D, and right-left 2D:4D (Dr-1), and vertical height in 3 different countermovement jump (CMJ) tests. A generalized additive model was employed to delineate age-related trajectories and predict CMJ performance. Our models yielded significant non-linear increases (or changes) in body size, current hormone concentration, training outcomes, and CMJ performance with chronological age. All 2D:4D measures were age invariant. The R2D:4D and testosterone were significant non-linear predictors of CMJ height with (R² = 66.2%) or without (R² = 54.3%) covariates, whereby a higher current testosterone concentration (up to a certain level) and a lower or higher R2D:4D were linked to better performance. The L2D:4D and Dr-1 had no predictive value. In conclusion, the R2D:4D and testosterone were co-predictors of CMJ height among athletic boys, with non-linear performance effects that differed in timing, tempo, and direction. Our findings confirm that testosterone can regulate a simple measure of boy's physical fitness through both an activational and organizational pathway.

Maternal Testosterone Concentrations in Third Trimester and Offspring Handgrip Strength at 5 Years: Odense Child Cohort

BACKGROUND

Maternal testosterone in pregnancy may have conditioning effects on offspring muscle strength.

PURPOSE

To investigate possible associations between maternal testosterone concentrations in third trimester and offspring handgrip strength (HGS) at 5 years.

METHODS

In the prospective, population-based Odense Child Cohort, total testosterone (TT) at gestational week 27-28 and 5-year HGS were measured in 1017 mother-child pairs. TT was measured by liquid chromatography-tandem mass spectrometry and free testosterone (FT) was calculated from TT and sex hormone-binding globulin (SHBG). Multivariable regression analyses were performed with HGS < 10th percentile as cutoff for low HGS.

RESULTS

Third-trimester FT concentration was 0.004 (0.002-0.007) nmol/L, geometric mean (mean - SD; mean + SD). The mean (SD) 5-year HGS was 8.7 (1.8) kg in boys and 8.1 (1.7) kg in girls (P < 0.001). Higher FT concentrations were associated with lower HGS (β = -0.186, P = 0.048), after adjustment for maternal age, parity, offspring sex, and 5-year height and weight. FT > 0.004 nmol/L was associated with higher risk of 5-year HGS < 10th percentile with odds ratios (95% CI) of 1.58 (1.01, 2.47; P = 0.047; n = 1,017) and 1.69 (1.05, 2.74; P = 0.032) after further adjustment for children's organized sports in subgroup analysis (n = 848). Lower HGS in relation to higher FT concentrations was found in all linear models but was not always statistically significant. HGS was not associated with maternal TT and SHBG levels.

CONCLUSION

Third trimester FT was inversely associated with offspring muscle strength assessed by HGS at 5 years of age, which may suggest a negative effect of maternal FT on offspring muscle strength.

Gender Differences and Relationship of 2D:4D-Ratio, Mental Toughness and Dark Triad Traits among Active Young Adults

Simple Summary

There is evidence that the exposure to more testosterone and less estrogen hormones before birth, that is, in utero, has a physiological impact on the relation between the index finger (2D) and the ring finger (4D). This relation is called the 2D:4D-ratio. A lower 2D:4D-ratio mirrors a longer ring finger (4D), relative to the index finger (2D); a higher 2D:4D-ratio mirrors a shorter ring finger (4D), relative to the index finger (2D). A higher exposure to testosterone and a lower exposure to estrogen hormones are associated with a lower 2D:4D-ratio. Further, a higher exposure to androgen hormones is associated with higher masculine traits. In the present study, we assessed 460 physically active young male and female adults. We showed that (1) males had lower 2D:4D ratios than females. Next, (2) active females and males had similar personality and mental toughness traits. (3) Females with more “dark” personality traits had a higher ability to perform consistently under stress and pressure; such females were mentally tougher. (4) Males with lower 2D:4D-ratios were mentally tougher. Overall, there is evidence that prenatal exposure to androgen hormones and personality traits in adulthood appear to be related, though, in a different fashion between male and female adults.

Abstract

There is consistent evidence that prenatal exposures to higher testosterone and lower estrogen concentrations during the first trimester of embryonal and fetal development are associated with a lower 2D:4D-ratio, which is to say: The index finger (2D) is shorter, compared to the ring finger (4D). Compared to non-active, athletes show lower 2D:4D ratios. However, athletes also report specific personality traits such as mental toughness, assertiveness, and competitive behavior. Here, we tested if 2D:4D-ratios were related to specific personality traits. We further investigated possible gender differences. A total of 460 active young adults (mean age: 24.81 years; 67% females) completed a series of self-rating questionnaires covering sociodemographic information and traits of the dark triad and mental toughness. Participants also provided a scan of their right palm hand to measure and calculate 2D:4D-ratios. t-tests, Pearson’s correlations, and multiple regression analysis were performed to analyze data. Compared to male participants, female participants had a higher 2D:4D-ratio. Female and male participants did not differ as regards dark triad traits and mental toughness traits. Irrespective of gender, and based on correlational computations, 2D:4D-ratios were unrelated to the dark triad (DT) and mental toughness (MT) scores. Higher DT scores were modestly associated with higher MT scores among females, but not among males. Lower 2D:4D-ratios were associated with higher constancy scores and the male gender. The constancy and male gender appeared to be associated with lower 2D:4D-ratios.

Using the TUG Test for the Functional Assessment of Patients with Selected Disorders

One of the tests used for quantitative diagnostics is Timed Up-and-Go (TUG), however, no reports were found regarding the percentage share of individual test components, which seems to have a greater diagnostic value in differentiating the functional status of the patients. The aim of the study was to analyze the percentage of the individual components of the TUG test in functional assessment in a population of healthy children and in clinical trials patients with various diseases. Material and Methodology. The material consisted of patients with orthopedic (n = 165), metabolic (n = 116) and neurological dysfunctions (n = 96). Results. The components of the TUG test that differentiated the studied groups of patients to the greatest extent were in the order: relapse tug3%, initial transition tug2%, sitting tug5% and standing up tug1%, while during the final transition tug4% statistically significant differences were found only between healthy children and the studied groups of patients. Conclusions. The TUG test turned out to be a good diagnostic tool, differentiating the studied groups of patients. The analysis of the percentage of the components of the TUG test can help in assessing the mobility of children and adolescents, monitor the effects of physiotherapy or the effects of surgical procedures.

Effects of Physical Exercise on the Body Composition and Conditional Physical Capacities of School Children During Confinement by COVID-19

As a result of the COVID-19 pandemic, most of the countries announced the temporary closure of schools, opting to continue classes virtually, affecting children's lifestyles, primarily by reducing the practice of physical activity and sport, which becomes a risk factor for the development of obesity and overweight. The objective of the present study was to determine the effects of physical exercise on body composition in a sample of school-age children during confinement by COVID-19. A quantitative approach study and quasi-experimental design with pre-test and post-test. The sample consisted of 70 school-age children from 8 to 12 years old who were randomly assigned to 2 groups: the experimental group (GE: 35), who received an aerobic and anaerobic physical exercise program 3 times a day. With a duration of 60 minutes for 10 weeks in a virtual way and a control group (CG: 35) that received only the physical education class. Although the pre-test post measurements showed favorable changes in body composition, weight, and conditional capacities (speed and jumping), these were not statistically significant (P < .05). A structured physical exercise program through virtuality for schoolchildren can be a strategy to control overweight and obesity in children during confinement and improve their conditional physical capacities (speed, jumping).

Handgrip strength and 2D : 4D in women: homogeneous samples challenge the (apparent) gender paradox

The length ratio between the second and the fourth digit (2D : 4D) is a retrospective, non-invasive biomarker for prenatal androgen exposure. It was found to be negatively correlated with handgrip strength (HGS) in men, but the evidence for women is mixed. Such studies in women call for increased detection sensitivity. The present study was designed to reduce potential confounding factors, especially age and ethnicity variation. We measured the digit ratios and HGS of 125 healthy women between 19 and 31 years of age from a remote region in Austria. 2D : 4D of both hands was significantly and negatively correlated with HGS (n = 125, right hand: r = -0.255, p = 0.002, left hand: r = -0.206, p = 0.011). Size, direction and significance of correlation coefficients remained stable when statistically controlling for age, body weight, body height, body mass index or hours of exercise per week. This yields theory-consistent evidence that HGS and 2D : 4D are clearly associated in women-when sufficiently reducing genetic variation (confounding 2D : 4D), the ontogenetic environment and age ranges (confounding HGS) in the study population. This finding implies similar organizing effects of prenatal androgens as in men, pointing to a more parsimonious developmental mechanism and a new look into its proximate and ultimate causes.

Understanding the Associations of Prenatal Androgen Exposure on Sleep Physiology, Circadian Proteins, Anthropometric Parameters, Hormonal Factors, Quality of Life, and Sex Among Healthy Young Adults: Protocol for an International, Multicenter Study

Background

The ratio of the second finger length to the fourth finger length (2D:4D ratio) is considered to be negatively correlated with prenatal androgen exposure (PAE) and positively correlated with prenatal estrogen. Coincidentally, various brain regions are sensitive to PAE, and their functions in adults may be influenced by the prenatal actions of sex hormones.

Objective

This study aims to assess the relationship between PAE (indicated by the 2D:4D ratio) and various physiological (sex hormone levels and sleep-wake parameters), psychological (mental health), and sexual parameters in healthy young adults.

Methods

This study consists of two phases. In phase 1, we will conduct a survey-based study and anthropometric assessments (including 2D:4D ratio and BMI) in healthy young adults. Using validated questionnaires, we will collect self-reported data on sleep quality, sexual function, sleep chronotype, anxiety, and depressive symptoms. In phase 2, a subsample of phase 1 will undergo polysomnography and physiological and genetic assessments. Sleep architecture data will be obtained using portable polysomnography. The levels of testosterone, estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, prolactin, melatonin, and circadian regulatory proteins (circadian locomotor output cycles kaput [CLOCK], timeless [TIM], and period [PER]) and the expression levels of some miRNAs will be measured using blood samples. The rest and activity cycle will be monitored using actigraphy for a 7-day period.

Results

In Poland, 720 participants were recruited for phase 1. Among these, 140 completed anthropometric measurements. In addition, 25 participants joined and completed phase 2 data collection. Recruitment from other sites will follow.

Conclusions

Findings from our study may help to better understand the plausible role of PAE in sleep physiology, mental health, and sexual quality of life in young adults.

International Registered Report Identifier (IRRID)

DERR1-10.2196/29199

Association of prenatal sex steroid exposure estimated by the digit ratio (2D:4D) with birth weight, BMI and muscle strength in 6- to 13-year-old Polish children

Objectives

The aim of this paper was to provide evidence for the impact of prenatal sex steroid exposure on prenatal and postnatal body size parameters, and muscle strength in children.

Methods

The following anthropometric data were studied in a group of 1148 children (536 boys and 612 girls) aged 6–13 years: the 2D:4D digit ratio, birth weight and length, and birth head and chest circumference. Postnatal parameters (6–13 years) included body weight and height, BMI, waist and hip circumference, WHR, as well as grip strength in both hands. All parameters that required it were adjusted for sex and gestational or chronological age. A general linear model, Pearson’s correlation, t-statistics and Cohen’s Δ were used in statistical analysis.

Results

Among birth size parameters, only birth weight was significantly negatively correlated with the 2D:4D digit ratio in children. Higher (feminized) digit ratios were significantly correlated with postnatal parameters such as body weight, BMI, and waist and hip circumference (positively), as well as hand grip strength–a proxy for muscular strength (negatively).

Conclusion

Problems with maintaining adequate body size parameters and muscle strength may be programmed in fetal life and predicted on the basis of the 2D:4D digit ratio. Body weight at birth and in early ontogenesis are additive correlates of the 2D:4D ratio. The present findings suggest that the 2D:4D digit ratio is related to postnatal phenotypes such as birth weight, overweight, and obesity as well as muscle strength in 6–13-year-old children of both sexes.

The relationship between the digit ratio (2D:4D) and vertical jump performance in young athletes

BACKGROUND

Digit ratio (2D:4D), a putative marker of prenatal testosterone, is a negative correlate of sports, athletic, and fitness performance.

OBJECTIVES

To describe the relationship between 2D:4D and vertical jump performance in athletes.

METHODS

Sixty-one Division I American Football players from a Midwestern U.S. university had their 2D:4D measured digitally and their vertical jump performance measured using jump mechanography. The primary outcome was jump height, with secondary outcomes depicting jump execution also recorded. Linear relationships between 2D:4D and vertical jump performance were quantified using partial correlations adjusted for age, height, mass, and ethnicity.

RESULTS

2D:4D was a statistically significant weak negative correlate of jump height (partial r [95% confidence interval]: -0.26 [-0.48, -0.01]), indicating that athletes with lower 2D:4Ds (i.e., relatively longer 4th digits) jumped higher. Relationships with jump execution variables were negligible to weak and negative, but not statistically significant.

CONCLUSIONS

The significant relationship between 2D:4D and jump height probably reflects both the long-term organizational and short-term activational benefits of testosterone. Therefore, 2D:4D may be a useful indicator of explosive strength among young athletes.

Digit ratio (2D:4D) and body mass index in the BBC Internet Study: prenatal sex steroids and a Trivers-Willard effect on body composition

Digit ratio - a putative measure of prenatal sex steroids - may be related to body mass index (BMI). However, reports of correlations between 2D:4D and BMI have yielded mixed results with some studies showing no relationship while others have reported positive associations in men or women only. This study considers associations between self-reported 2D:4D and BMI in a large online survey (i.e. the BBC Internet Study). At the individual level, there was a weak positive association between 2D:4D and BMI in both sexes with greater effect sizes in women. Body mass index was positively related to age and negatively related to parental income; however, the relationship between 2D:4D and BMI was independent of both variables. At the national level, mean 2D:4D per country showed positive associations with mean national BMI but those correlations were restricted to females. It is concluded that BMI is positively related to low prenatal testosterone and high prenatal oestrogen. Parental income inequality may influence both prenatal sex steroids (through a 'Trivers-Willard' effect) and BMI such that increases in inequality result in reductions in prenatal testosterone and increases in BMI at the individual and national level.

Radiographic digit ratios (2D:4D) of Afro-Caribbean children: Comparisons with published data from white children

BACKGROUND

Digit ratio (2D:4D) from soft-tissue measurements of fingers from children and adults from Black and White ethnic groups show sex differences (males<females) and group differences (Black< White). However, less is known about such differences in radiographic 2D:4D.

AIM

To consider sex and ethnic differences in radiographic 2D:4D of children of Afro-Caribbean descent and to compare these means with "standards" from White children.

SUBJECTS AND METHODS

A cross-sectional design with samples from Afro-Caribbean children aged 6 to 11 years compared to published radiographic measurements for White children in the Fels Longitudinal Study.

RESULTS

Radiographic 2D:4D showed ethnic differences such that Afro-Caribbeans<Whites. There was an age-stable right-side sex difference (boys<girls) in the 2D:4D of the distal phalanx and the distal soft-tissue tip in the Afro-Caribbean children but not in the proximal- and middle-phalanges or the composite length of the phalanges. Sex differences in 2D:4D (boys<girls) were present in the White children in the middle and proximal phalanges and composite phalange length but not in the distal phalanx.

CONCLUSION

In Afro-Caribbean children, mean radiographic 2D:4D was lower than that of White children and sexual dimorphism of 2D:4D (boys<girls) was confined to the distal phalanx and fingertip soft-tissue. In contrast in White children, there were no sex differences in the distal phalanx but there were in the middle-, proximal and composite phalanges (boys<girls). We discuss whether these differences in 2D:4D are widespread among Blacks and Whites and the implications for the interpretation of radiographic 2D:4D and morphological soft-tissue 2D:4D across macro-ethnic groups.

The association between 2D:4D ratio and aggression in children and adolescents: Cross-cultural and gender differences

BACKGROUND

Two recent meta-analyses have suggested the association between digit ratio (2D:4D) and aggression is weak. This conclusion has been criticised because the meta-analyses conflate forms of aggression that show strong sex differences with those that do not, and most studies have considered post-pubertal participants.

AIMS

We test the influence of 2D:4D and ethnicity in the expression of aggression in children and adolescents in four ethnic groups of European and African origin.

STUDY DESIGN

Buss and Perry aggression questionnaire. Direct measurement of the 2nd and 4th digits.

SUBJECTS

1296 children and adolescents from Tanzania and Russia from 4 ethnic groups - Datoga, Meru, Russians, Tatars.

RESULTS

There were ethnic and gender differences in ratings on aggression with boys consistently reporting more physical aggression. In all four samples right 2D:4D was significantly lower in boys, compared to girls. With regard to our total sample of boys, the right 2D:4D was significantly and negatively associated with self-ratings on physical aggression, but no association was found for left 2D:4D. No associations between 2D:4D and physical aggression were found for girls. Hostility was negatively correlated with 2D:4D for boys, and anger was positively correlated with 2D:4D in girls.

CONCLUSION

Sex differences were strongest for right 2D:4D (boys<girls), and for physical aggression (boys>girls). Right 2D:4D was negatively related to physical aggression in boys only, suggesting possible relationship to prenatal androgenization.

Strength and competitiveness are more strongly predictive of retrospective sport participation than 2D:4D in university-aged women

Objective: Females continue to participate in sport at lower rates than males. Girls who participate in sport gain many advantages. Even with programs designed to emphasize participation, some females continue with sport participation while others do not. Given the advantages and controversies surrounding testosterone and female sport, it is possible that testosterone may predispose females toward sport participation. Our objective was to determine if the second to fourth digit (2D:4D) ratio, a proxy for prenatal androgen exposure, correlates with sport participation throughout female adolescence and young adulthood. Methods: A cross-sectional analysis of indirect prenatal androgen exposure (i.e., 2D:4D) was completed on 18–30-year-old women ( n = 92) using demographics, anthropometrics, sport-specific behaviour tendencies, and retrospective sport participation. Results: 2D:4D was not significantly correlated with total sport participation (TSP) ( r = −0.065, p = 0.538). Secondary analyses revealed significant correlations between TSP and maximum hand grip ( r = 0.406, p = 0.000) and the Sport Orientation Questionnaire (SOQcomp ( r = 0.513475, p = 0.000), SOQgoal ( r = 0.253, p = 0.015), SOQwin ( r = 0.366, p = 0.000)). Conclusion: Although strength and competitiveness are strongly correlated with female sport participation, the impact of prenatal androgen exposure (i.e., 2D:4D) remains to be determined given its weak and negative association with female sport participation. Given that females participate in sport at lower rates than males, continuing to determine what factors influence sport participation is an important goal.

Digit ratios and motor and health-related fitness in pre-adolescent females

Background: Assessing different aspects of physical fitness in children whose abilities are undeveloped and their associations with second-to-fourth digit ratio (2D:4D) may better determine the potential athleticism of an individual.Aim: The purpose of the study was to examine relationships between the digit ratios and selected motor and health-related fitness parameters in a large sample of pre-adolescent females.Subjects and methods: Participants included 8-12 year old Iranian and Afghan girls. The length of the left and right second and fourth digits was measured by scanning and computer-assisted image analysis. Motor- and health-related fitness tests were evaluated.Results: No significant correlations were noted between right 2D:4D ratio and physical fitness components. Left 2D:4D and physical fitness components were not correlated, with the exception of handgrip strength (r = -0.193). However, right and left second digit lengths were negatively correlated with predicted VO_2max (p ≤ 0.01). In addition, right-left 2D:4D was significantly negatively correlated with flexibility, and significantly positively correlated with height and body fat percentage.Conclusion: In contrast to previous investigations, it seems that left 2D:4D is a predictor of strength, but not aerobic exercise. It is suggested there may be a potential relationship between prenatal androgen exposure and high flexibility, low body fat percentage and the generation of muscular strength in pre-adolescent females.

Sex differences in relationship between body composition and digit length ratio (2D:4D) in students of military courses

It is believed that the second to fourth finger length ratio is an indirect indicator of fetal testosterone levels. It is pointed out that there is a relationship between the 2nd to 4th finger length ratio and the body structure in women and men. Studies on the relationship between body composition and 2D:4D finger length among military students have not been carried out so far. The work aims to determine the dependence of body composition and the quotient of the 2nd and 4th fingers length of military students. The research material has been gathered as a result of examinations of women and men studying military subjects. The study involved 55 women and 65 men. The tests included anthropometric measurements (body height, body weight, length of the second and the fourth fingers) and body composition measurements. As a result of the tests, no dimorphic differentiations in the digit length ratio (2D:4D) was indicated. The BMI, muscle mass, lean body mass and water in the body demonstrated higher values in men than in women. However, the fat content in men was low. It was found that the relationship exists between muscle mass, lean mass and total water content in the body and the 2D:4D finger length ratio in the left hand in women. A higher level of fetal testosterone, characterized by lower values of the 2nd to 4th finger length ratio, may be associated with a higher content of muscle mass, lean body mass and water in the body of adult women leading a similar lifestyle.

Association between the digit ratio (2D:4D) and body fat distribution in Mordovian students

BACKGROUND

The length ratio of the second to the fourth finger (2D:4D) is a possible biomarker of prenatal sex hormone levels, which play a significant role in determining sex-related body traits.

AIMS

To evaluate the value of the 2D:4D ratio in a Mordovian sample and to test the associations between the 2D:4D ratio and sexually dimorphic morphological traits, such as height and body weight, body mass index, waist and hip circumference, the waist-to-hip ratio, handgrip strength and the skinfold thickness.

SUBJECTS AND METHODS

The sample studied included 106 individuals of Mordovian ethnicity: 58 males and 48 females, 16-23 years old. The associations between the 2D:4D ratio and morphological traits were evaluated by multivariate regression analysis and correlation analysis.

RESULTS

The 2D:4D ratio in males was significantly lower than in females. Most of the associations of the 2D:4D ratio with morphological traits were statistically insignificant. The 2D:4D ratio is only significantly correlated with skinfold thickness of the forearm and the abdomen in females.

CONCLUSION

The association between the 2D:4D ratio and skinfold thickness is indicative of the role of prenatal sex hormones in shaping the body fat distribution in females, along with the significant impact of sex hormones at puberty.

Association of the 2D:4D digit ratio with body composition among the Polish children aged 6-13 years

The 2D:4D digit ratio is formed as a result of genetic factors but also prenatal exposure to sex hormones. The higher index value the higher concentration of the prenatal oestrogen. It is commonly known that testosterone is a hormone connected with muscle mass growth and that oestrogen affects adipogenesis. The aim of this study was to find if the digit ratio can be an informative indicator of the fat mass and muscle mass and body proportions in prepubertal children. Material and methods The analysed cohort included 420 children (221 girls and 199 boys) aged 6-13 years. Pearson's and Spearman's tests were conducted to assess whether 2D:4D was significantly correlated with the body composition measurements. Multiple regression models and stepwise forward regression were applied to select the most important independent variables affecting fat mass (%) and muscle mass (%) as well as the BMI and the WHR. Results The study shows that the digit ratio is negatively correlated with muscle mass (MM%) among girls (p < 0.05).There was no similar relationship in the group of boys. The regression models showed a significant role in determining the body composition and body proportions played by maternal factors such as: maternal level of education and weight gain during pregnancy. Conclusions The 2D:4D digit ratio seems to be an informative indicator of the muscle mass development since girls' early childhood. Moreover, maternal environment is also important in forming the offspring's body composition and proportions.

Digit ratio (2D:4D) and behavioral symptoms in primary-school aged boys

The second-to-forth digit length ratio (2D:4D) is considered to be a biomarker for intrauterine androgen levels. It is associated with adult and child mental health problems, primarily with behavioral symptoms and predominantly in males. Using a cross-sectional design, we examined whether 2D:4D was associated with conduct disorder (CD) symptoms in 138 primary-school aged children (54% boys, M_age = 7.70 years) and considered child sex as a moderating factor. Children's digit lengths were measured from hand scans and mothers rated the behavioral/emotional symptoms of their child. The regression analyses revealed that 2D:4D ratios were associated with behavioral symptoms in boys (β = -0.260, p = 0.026), but not in girls (β = -0.040, p = 0.762). Child emotional symptoms, analyzed as a control, were not significantly correlated with 2D:4D. In conclusion, prenatal brain hyperandrogenization - operationalized by the 2D:4D biomarker - could result in behavioral symptoms in boys at early school age, reflecting one predictor for early onset CD. Our data support the use of 2D:4D as a marker of prenatal androgen exposure.

Digit ratio (2D:4D) and muscular strength in adolescent boys

Using a cross-sectional design, this study quantified the relationship between the digit ratio (2D:4D) and muscular strength in 57 adolescent boys. 2D:4D was very likely a moderate negative correlate of handgrip strength, even after adjustment for age and body size. This result may reflect the organizational benefits of prenatal testosterone.

Thou Shalt Not Bear False Witness Against Null Hypothesis Significance Testing

Null hypothesis significance testing (NHST) has been the subject of debate for decades and alternative approaches to data analysis have been proposed. This article addresses this debate from the perspective of scientific inquiry and inference. Inference is an inverse problem and application of statistical methods cannot reveal whether effects exist or whether they are empirically meaningful. Hence, raising conclusions from the outcomes of statistical analyses is subject to limitations. NHST has been criticized for its misuse and the misconstruction of its outcomes, also stressing its inability to meet expectations that it was never designed to fulfil. Ironically, alternatives to NHST are identical in these respects, something that has been overlooked in their presentation. Three of those alternatives are discussed here (estimation via confidence intervals and effect sizes, quantification of evidence via Bayes factors, and mere reporting of descriptive statistics). None of them offers a solution to the problems that NHST is purported to have, all of them are susceptible to misuse and misinterpretation, and some bring around their own problems (e.g., Bayes factors have a one-to-one correspondence with p values, but they are entirely deprived of an inferential framework). Those alternatives also fail to cover a broad area of inference not involving distributional parameters, where NHST procedures remain the only (and suitable) option. Like knives or axes, NHST is not inherently evil; only misuse and misinterpretation of its outcomes needs to be eradicated.

Digit ratio (2D:4D) and postoperative pain perception

BACKGROUNDS

It has not been established whether sex differences in pain perception are influenced by prenatal sex hormones. Digit ratio as an indicator of prenatal hormone exposure can be used as a simple measure of the influence of prenatal hormones on pain sensitivity or perception in adulthood.

OBJECTIVE

The aim of this study was to determine a correlation between the 2D:4D ratio and pain perception in the postoperative period after rhinoplasty.

METHOD

A prospective cohort study of 100 patients (50 women of the mean age of 30.74±8.09years and 50 men of the mean age of 30.98±10.86years) who underwent posttraumatic rhinoplasty due to the nose trauma in Plastic, Reconstructive and Aesthetic Surgery Clinic. The following measurements were taken the day before a surgery: body height, waist and hip circumference, II and IV digits' lengths and body weight. All subjects filled in a questionnaire including 0-10-point VAS scales to assess postoperative pain 1h after an operation (AO), 6h AO, 12h AO, 24h AO and 48h AO.

RESULTS

Women with low 2D:4D reported significantly more pain 1h after an operation than women with high 2D:4D. Similar correlation was observed for low 2D:4D in women 48h AO. In men, low 2D:4D was associated with lower postoperative pain 12h AO (p=0.029).

CONCLUSION

In conclusion, we showed that low 2D:4D in women was associated with high postoperative pain, and low right 2D:4D in men was associated with low postoperative pain. This may suggest that intrauterine estrogen exposure makes women more resistant to pain.

Digit ratio (2D:4D) and handgrip strength are correlated in women (but not in men) in Hui ethnicity

INTRODUCTION

Digit ratio, especially second-to-fourth digit ratio (2D:4D) is used as a biomarker of prenatal testosterone exposure and was found associated with physical ability, such as handgrip strength (HGS). Recently, this association has been discussed in several ethnic groups.

AIMS

To investigate correlations between 2D:4D and HGS in Chinese population of Ningxia Hui ethnicity.

METHODS

Here we firstly present the evidence on digit ratio and HGS of 346 college students (119 males and 227 females) by collecting photographs and HGS of both hands at Yinchuan city, in the Ningxia province of China.

RESULTS

Females have higher mean values of digit ratio than males; significant variances of 3D:5D (left and right: P<0.05), 2D:3D, 3D:4D (left and right: P<0.01) and 2D:4D, 2D:5D (left and right: P<0.001) were found between different sex. Males showed significantly greater HGS than females on both hands. 2D:4D of both hands were significantly negative correlated with HGS in females (but not in males).

CONCLUSIONS

2D:4D ratio is negatively correlated with HGS in a Chinese population (especially in females) of Ningxia Hui ethnicity.

Why is digit ratio correlated to sports performance?

Second to fourth digit ratio is the ratio of second to fourth digit length. It has been known that digit ratio is sexually dimorphic in humans, such that males tend to have lower digit ratio (longer fourth digits relative to second digits) than females. Digit ratio is thought to be a biomarker of the balance between fetal testosterone (FT) and fetal estrogen (FE) in a relatively narrow developmental window at the end of the first trimester of pregnancy. On the contrary, the relationships between digit ratio and levels of sex steroids in adults are not clear. Most correlational studies between digit ratio and adult sex steroids have revealed that this association is statistically not significant. However, for many years, a lot of researches showed negative relationships between digit ratio and sports performance such as rugby, surfing, rowing, sprinting, endurance, and hand grip strength. Here, we discuss possible mechanisms about the relationships between digit ratio and sports performance.

Digit ratio (2D:4D) and handgrip strength in a Chinese population of Han ethnicity

BACKGROUND

In humans, the relative lengths of the index finger to the ring finger (2D:4D) is a sexually dimorphic trait which correlated with prenatal sex steroids and has been increasingly used as a promising tool to evaluate the impact of prenatal hormone exposure in some traits, such as physical performance. Handgrip strength (HGS) is one potent index of physical ability and its relationship with 2D:4D ratio has been discussed in several ethnic groups.

AIMS

To investigate whether there is a correlation between 2D:4D ratio and HGS in Chinese college students of Ningxia Han ethnicity.

METHODS

608 students (211 males and 397 females) of Han ethnicity were recruited from Ningxia medical university. Photocopies and HGS of both hands were collected at Yinchuan city, in the Ningxia province of China.

RESULTS

Sexual dimorphism of 2D:4D and HGS were found, males had significantly lower 2D:4D and greater HGS than females. 2D:4D in both hands were significantly negative correlated with HGS in females and not in males.

CONCLUSIONS

2D:4D ratio is negative correlated with HGS in a Chinese population of Ningxia Han ethnicity and this association should be considered on the anthropological research within an evolutionary concept in the future.

SPORTS PREFERENCE AND DIGIT RATIO (2D:4D) AMONG FEMALE STUDENTS IN WROCŁAW, POLAND

Humans exhibit sex differences in competitiveness, sensation seeking and risk-taking attitude, which are required in sports. These attributes are often linked to prenatal testosterone (PT) exposure. The second-to-fourth digit length ratio (2D:4D) is an indicator of PT exposure. A lower 2D:4D indicates higher PT exposure and vice versa. Males generally have a lower 2D:4D than females. Sensation- and/or thrill-seeking behaviours have also been found to be negatively associated with 2D:4D. Boxing and judo are considered to be high-risk sports. Voluntary participation in judo/boxing in contrast to aerobics can be guided by such behaviours and thus have an association with lower 2D:4D. This cross-sectional study included 167 female students from a military academy in Wrocław, Poland. Of them, 119 had voluntarily chosen aerobic exercise, and 48 opted for judo/boxing. Height, weight and second and fourth digit lengths were measured. Physical fitness was assessed using Eurofit tests. The two groups showed similar physical fitness and body size. However, the judo/boxing group had significantly lower mean 2D:4D values than the aerobics group. It is proposed that voluntary choice of participation in a sport discipline by women could be linked to the ‘organizational’ effect of intrauterine testosterone exposure during prenatal growth.

Digit ratio (2D:4D), testosterone, cortisol, aggression, personality and hand-grip strength: Evidence for prenatal effects on strength

BACKGROUND

Digit ratio (2D:4D) is a putative marker for prenatal testosterone and is correlated with performance in many sports. Low 2D:4D has been linked to strength but the evidence is mixed and strength is also influenced by mass, testosterone, and behavioural factors. It has been hypothesised that the 2D:4D-strength correlation may be strongest in challenge conditions when short-term changes occur in steroid hormones.

AIMS

We tested this suggestion in men.

STUDY DESIGN

We used a cross-over study design with a challenge (an aggressive video of rugby tackles) and control (a blank screen) condition.

SUBJECTS

89 healthy men.

OUTCOME MEASURES

Finger lengths (2nd and 4th for both hands), hand-grip strength (HGS), testosterone (T), cortisol (C), aggression (Buss-Perry Aggression Questionnaire) and personality type (Ten Item Personality Measure). In both conditions participants provided saliva samples (for hormone assays).

RESULTS

In the challenge condition there was a highly significant increase in HGS, and modest changes in T, physical aggression and emotional stability. HGS correlated negatively with left hand 2D:4D. In a multiple regression, left hand 2D:4D was negatively related to HGS and emotional stability was positively related to HGS. In the control condition HGS was not correlated with 2D:4D. In a multiple regression, BMI, physical aggression, and emotional stability were significantly related to HGS.

CONCLUSIONS

2D:4D is a negative correlate of strength in challenge situations. This finding may in part explain associations between 2D:4D and sports performance.