2D:4D ratios predict hand grip strength (but not hand grip endurance) in men (but not in women)

Grip strength of law enforcement officers and its implications

Grip strength (GS) plays a vital role for law enforcement officers (LEOs). This study aimed to establish a baseline for LEO GS, compare it with the general population, determine the correlation between LEO GS and body dimensions, and evaluate the implications for occupational performance. A total of 756 male and 218 female LEOs from across the U.S. participated in the study. On average, male LEOs exhibit stronger GS (49.53 kg) than female officers (32.14 kg). Significant differences between LEOs and the general population were observed. GS correlated with hand breadth, hand length, stature, and bideltoid breadth. Approximately 26%-46% of males and 5%-39% of females were identified as being at risk of health, fit, or occupational performance based on their measured GS. Enhancing GS training or avoiding implementing heavy equipment (such as pistols with heavy trigger weight), could improve officer occupational performance, safety, or health.

Associations of Facial Shape With Physical Strength and 2D:4D in a Turkish Male and Female Sample

OBJECTIVE

Human sexual dimorphism in physical strength manifests itself in men having a greater muscle mass than women, reflecting ancestral roles in competition, protection, and provisioning. Prenatal testosterone exposure, approximated via the second-to-fourth digit ratio (2D:4D), is linked to increased muscular strength in both sexes, indicating a developmental influence. Previous research has shown that both physical strength and 2D:4D have facial shape correlates, especially in men, but most studies have focused on Western populations and one trait. We therefore hypothesized a broader relationship between facial shape and both physical strength and 2D:4D.

MATERIALS AND METHODS

In this study, we quantified the association between facial shape, handgrip strength (HGS), and 2D:4D in a non-Western Turkish sample (72 men, 55 women; Md = 22 y, SIR = 1.8 y) using two dimensional geometric morphometrics. Thirty-eight somatometric and 32 semi-landmarks were digitized on facial photographs taken in frontal view. Physical strength was assessed via handgrip strength (HGS), and the second digit length was divided by the fourth digit length to calculate 2D:4D.

RESULTS

Both HGS and 2D:4D were significantly associated with shape in both sexes, but only in men did they explain a significant amount of facial variation. Thin-plates spline deformation grids and geometric morphometric morphs visualized the facial shape changes related to variations in handgrip strength, 2D:4D, and sexual dimorphism, enabling trait comparisons.

CONCLUSION

This study contributes a comparative sample from the Middle East, which is indispensable to discern universalities from Western peculiarities. It provides evidence to better understand the biological basis of facial traits, which can potentially serve as increasingly relevant social cues in today's online and digital environments.

The change in handgrip strength, after physical exercise, is moderated by digit ratio (2D:4D): A study among the young adults in Poland

BACKGROUND

The digit ratio (2D:4D), the ratio of the lengths of second (2D) to the fourth (4D) fingers, is a proxy indicator of prenatal androgen exposure. On average, males display lower 2D:4D than females. Previous studies have shown that lower 2D:4D ratios were associated with better sports and physical abilities.

AIM

To assess whether a challenge condition, imposed by intense exercise, could increase handgrip strength (HGS) associated with 2D:4D.

METHODS

This cross-sectional experimental study included 90 healthy young Polish adults (40 males, 50 females). They underwent intense physical exercise, before (7 days) and after which they were measured for HGS and 2D:4D. Height and weight were also measured. Analyses of Covariance were employed to delineate associations.

RESULTS

2D:4D had significant predictive effects on the differences in HGS (DHGS) measured in two occasions, without and after, physical exercises. The lower was the 2D:4D, the higher the DHGS, particularly, for the left hand.

CONCLUSION

The results reconfirmed that the link between prenatal testosterone exposure (indicated by 2D:4D) and physical strength depends on the context, such as a challenged condition.

Early developmental masculinization among boys: More prenatal testosterone action (assessed via 2D:4D) renders their faces perceived as masculine but not pretty or cute

The 'organizational-activational hypothesis' posits that the fetal environment has a lasting impact on offspring physical, cognitive, and behavioral phenotype. An established biomarker for human prenatal testosterone exposure is the second-to-fourth digit ratio (2D:4D). While related facial characteristics and their social perceptions have been investigated in young adults, studies focusing on younger or older age groups are scarce. Standardized facial photographs of 17 Austrian boys aged 4 to 11 years were each rated by 162 adults in Austria (78 female, 84 male) for masculinity, dominance, physical strength, maturity, independence, cuteness, and prettiness. Following high interrater agreement (Cronbach's alphas >0.96), average ratings per face were subjected to a principal component analysis. The first principal component (52 % var. expl.) correlated positively with the boys' age (r = 0.685), whereas the second principal component (37 % var. expl.) reflected organizational effects of prenatal androgen exposure (i.e. androgenization), as shown by a negative correlation with the boys' 2D:4D (r = -0.487). Geometric morphometrics was employed to extract the facial shapes corresponding to these two principal components. Overall, adults consistently attributed masculinity in line with prenatal testosterone exposure, whereby masculinity was assessed as neither pretty nor cute. In contrast to findings within adults, boys' face ratings of dominance and physical strength did not correspond with their masculinity assessments, but rather with the social attributions reflecting age-related developmental progress (maturity and independence). This adds an ontogenetic layer of complexity. Prenatal testosterone exposure influences the development of boys' facial features, which in turn even shape social stereotypes in adults.

Associations between 2D:4D from direct and radiographic measurements with handgrip strength in young adult Tuvans

BACKGROUND

Digit ratio (2D:4D) - the relative lengths of the index and ring finger - is sexually dimorphic (male < female), possibly because of the sex-differentiated impact of prenatal androgenization on fetal development in the 1st trimester. The sex difference remains stable with age and has been reported in children, adolescents, and adults from industrialized and non-industrialized societies. Handgrip strength (HGS) also is sexually dimorphic (males > females) and correlates negatively with 2D:4D.

AIMS

To examine in a sample of young adult Tuvans from Siberia (Russian Federation): i) the association between 2D:4D measured directly from the palms with 2D:4D measured from radiographic images of the same individuals and ii) the associations between 2D:4D and HGS in Tuvan men and women.

STUDY DESIGN AND SUBJECTS

The study was cross-sectional. Participants were Tuvans (n = 185; 80 men; mean age = 21.02 years). 2D:4D was measured with a caliper from the ventral surface of the palm (both hands) and from radiographic images (left hand). HGS of both hands was measured with a digital hand dynamometer. Body height and weight were measured with an anthropometer and a body composition scale.

RESULTS

2D:4D ratios and anthropometric measures (including HGS) were sexually dimorphic. Men had lower 2D:4D and higher HGS than women. Direct measures of 2D:4D correlated positively with 2D:4D measured from radiographs. Body mass index (BMI) was a significant predictor of HGS for both sexes. Male right 2D:4D and female right and left 2D:4D correlated negatively with HGS after controlling for the influence of BMI. There were no associations with radiographic measurements of 2D:4D.

CONCLUSION

Our findings provide evidence of sexual dimorphism in 2D:4D among young adult Tuvans. Together with previous research on Tuvan children and adolescents, these findings provide clear evidence of 2D:4D sexual dimorphism in pre- and postpubertal Tuvans. The small negative association between 2D:4D and HGS corresponds to similar reports across populations, suggesting that 2D:4D is a weak correlate of muscular fitness.

Anthropometrics, Performance, and Psychological Outcomes in Mixed Martial Arts Athletes

The digit ratio (2D:4D) is related to prenatal testosterone (T) and sports performance. Few investigations have explored 2D:4D in determining the potential performance of individuals in power-based sports, specifically combat sports. This study compared 2D:4D between mixed martial arts (MMA) athletes and non-athletes and investigated the association between (1) handgrip strength (HGS) and lean body mass (LBM) with 2D:4D in MMA athletes and (2) psychometric variables and 2D:4D in MMA athletes and non-athletes. In total, 122 men participated in this study (53 non-athletes, 45 professionals, and 24 amateur fighters). The 2D:4D was measured using a caliper, HGS was assessed with a dynamometer, and psychometric variables were evaluated using questionnaires. Athletes displayed significantly (p < 0.05) lower median values of right (0.95 ± 0.04) and left (0.96 ± 0.03) 2D:4D in comparison with non-athletes, (0.97 ± 0.03) and (0.99 ± 0.03), respectively. We observed that left hand 2D:4D was negatively correlated with HGS (r = −0.43; p < 0.05) and lean body mass (r = −0.49; p < 0.05) in professional athletes. Professional athletes also displayed significant differences (* p < 0.05; ** p < 0.001) in psychometric variables compared to non-athletes for (1) agreeableness **, median values (interquartile range) = −0.11 (−0.19−0.07) and 0.2 (−0.09−0.33), respectively; (2) anger **, mean ± standard error = 2.40 ± 0.12 and 2.89 ± 0.89, respectively; and (3) openness *, mean ± standard error = 0.17 ± 0.04 and −0.006 ± 0.04, respectively. However, we did not observe an association between psychometric variables or wins with 2D:4D. In conjunction with other measures, 2D:4D is valuable in determining the potential athleticism of an MMA athlete.

Associations between bio-motor ability, endocrine markers and hand-specific anthropometrics in elite female futsal players: a pilot study

BACKGROUND

The second-to-fourth digit ratio (2D:4D) has been calculated for individual athletes and sports, but it has not been investigated in futsal performance. Therefore, the aim of this study was to investigate any relationships between 2D:4D of the dominant and non-dominant hands and physical capacity performances, selected functional variables and hormone concentrations in elite female futsal players.

METHODS

Twenty-four elite female futsal players were measured for 2D:4D in the dominant (2D:4D_D) and non-dominant (2D:4D_ND) hand. The futsal specific performance test (FSPT), hand-grip strength (HGS) and aerobic power were also assessed. In addition, selected circulatory hormones were measured (estradiol, cortisol, growth hormone and insulin like growth factor-1). Pearson's correlation test was used to identify correlational relationships.

RESULTS

Total test-time and performance time (total time + penalty time) for the FSPT showed a significant correlation with 2D:4D_D (r = 0.53, p = 0.005 and r = 0.55, p = 0.003, respectively). HGS_ND also displayed a significant correlation with the 2D:4D_D (r = 0.59, p = 0.002). Aerobic power and time spent running on the treadmill also showed a significant relationship with 2D:4D_ND (both, r = 0.54, p = 0.006). Cortisol showed a significant correlation with 2D:4D_D (- 0.58, p = 0.003) and 2D:4D_ND(- 0.52, p = 0.008).

CONCLUSIONS

The measurement of 2D:4D ratio could be an important factor in determining potential performance attributes and talent identification of elite female futsal players. Further studies are needed in this area to further examine the results presented here.

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.

The relationship between digit ratio (2D:4D) and muscular fitness: A systematic review and meta-analysis

BACKGROUND

Digit ratio (2D:4D), a marker of prenatal testosterone exposure, is a weak negative correlate of sports/athletic/fitness performance. While numerous studies have examined the relationship between 2D:4D and physical fitness, there has never been a comprehensive study that has synthesized studies examining relationships between 2D:4D and muscular fitness.

OBJECTIVES

To systematically review and meta-analyze the relationship between 2D:4D and muscular fitness measured as handgrip strength (HGS).

METHODS

We systematically searched five electronic databases, reference lists, topical systematic reviews/meta-analyses, and personal libraries in November 2020. Peer-reviewed, cross-sectional studies that reported Pearson's correlation coefficients between objectively measured 2D:4D and HGS were included. We used random-effects meta-analysis to estimate the pooled correlation and the 95% confidence interval (95%CI), and moderator analyses to estimate the influence of sex and age.

RESULTS

Data from 22 studies, representing 5271 individuals from 11 countries ranging in (mean) age from 10.4 to 58.0 years, were included. Overall, there was a weak negative correlation between 2D:4D and HGS (r = -0.15, 95%CI = -0.20 to -0.09), indicating that individuals with low 2D:4Ds had high HGS. We found substantial heterogeneity between studies (Q = 123.4, p < .0001; I²  = 74%), but neither sex (Q = 0.003, p = .96) nor age (Q = 0.46, p = .50) significantly moderated the pooled correlation.

CONCLUSIONS

We found a weak negative relationship between 2D:4D and HGS, which showed substantial heterogeneity between studies, but was neither moderated by sex nor age. Our finding probably reflects both the long-term (organizational) and short-term (activational) benefits of testosterone.

Get a Grip: Variation in Human Hand Grip Strength and Implications for Human Evolution

Although hand grip strength is critical to the daily lives of humans and our arboreal great ape relatives, the human hand has changed in form and function throughout our evolution due to terrestrial bipedalism, tool use, and directional asymmetry (DA) such as handedness. Here we investigate how hand form and function interact in modern humans to gain an insight into our evolutionary past. We measured grip strength in a heterogeneous, cross-sectional sample of human participants (n = 662, 17 to 83 years old) to test the potential effects of age, sex, asymmetry (hand dominance and handedness), hand shape, occupation, and practice of sports and musical instruments that involve the hand(s). We found a significant effect of sex and hand dominance on grip strength, but not of handedness, while hand shape and age had a greater influence on female grip strength. Females were significantly weaker with age, but grip strength in females with large hands was less affected than those with long hands. Frequent engagement in hand sports significantly increased grip strength in the non-dominant hand in both sexes, while only males showed a significant effect of occupation, indicating different patterns of hand dominance asymmetries and hand function. These results improve our understanding of the link between form and function in both hands and offer an insight into the evolution of human laterality and dexterity.

Masculinity and immune system efficacy in men

Masculinity-related morphological traits are supposed to be honest indicators of a man's biological quality. While some studies showed that sexually dimorphic traits are related to various aspects of biological condition such as general health, immunity or fertility, still little is known about the relationship between masculine traits and the effectiveness of innate and adaptive immunity in humans. The aim of this study was to see if masculine traits, which are dependent on androgen levels in foetal and pubertal stages of development, are related to the immune quality in healthy men. The immune quality was evaluated for 91 healthy men aged 19-36 years. Immunity measurements included innate and adaptive parameters. General health status, age, testosterone level, BMI, physical activity, and smoking were controlled. The shoulder-to-hip ratio (SHR), 2D:4D digit ratio and hand-grip strength (HGS) were used as markers of masculinization. The regressions showed that when controlling for confounds, masculinity-related traits were in general not related to innate and adaptive immunity. Only a weak association was observed for right 2D:4D ratio and T-lymphocyte counts (but it becomes non-significant after adjustment for multiple comparisons). Our results do not support the premise that masculinity is a cue for immunological quality in men. However, the positive association between right 2D:4D and T lymphocytes might suggest that further studies are needed to verify if androgen stimulation in prenatal development might be related to immunity in adulthood.

Digit ratio (2D:4D) moderates the change in handgrip strength on an aggressive stimulus: A study among Polish young adults

BACKGROUND

The ratio of the lengths of second finger (2D) to the fourth (4D) is a putative indicator of foetal hormonal exposure. The link between 2D:4D and physical strength or sports performance in not consistent. It was suggested that the association of 2D:4D with the sporting and physical ability is better demonstrated in the context of challenge and competition, either real or simulated. However the evidence is limited to a few studies till date.

AIM

The objective of this study was to assess whether an aggressive video show could increase muscular strength and if 2D:4D moderated such increase.

STUDY DESIGN

We compared outcome measures in two experimental conditions.

OUTCOME MEASURES

Lengths of second (2D) and fourth (4D) digits and their ratio (2D:4D) for both hands, height and weight, handgrip strength of both hands.

SUBJECTS

250 healthy young adults (76 female).

RESULTS

The mean left-, right- and average HGS values increased after aggressive video watching than after control blank screen show. The increase was higher in females compared to males. The increase was higher among the individuals with lower 2D:4D, more clearly among females.

CONCLUSIONS

The 2D:4D correlated negatively with HGS after exposure to challenge condition and this relationship is pronounced in females than males. Thus there is link between prenatal androgenisation and enhanced physical power in challenge situation.

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.

College-aged women in the United States that play overhand throwing sports have masculine digit ratios

Athletic prowess in both males and females is negatively correlated with the ratio between the lengths of the second and fourth fingers (2D:4D), a correlate of prenatal testosterone exposure. Because multiple lines of evidence suggest that prenatal testosterone exposure is associated with sports interest, motivation, and athletic performance we measured the digit ratios of 77 non-athletes, 103 varsity athletes, and 78 club sport athletes to test 8 hypotheses about the relationship between digit ratio and the athletic behavior of college-age women in the USA. Using independent samples t-tests, we found no significant differences between the digit ratios of women that (1) were athletes and non-athletes, (2) were varsity or club sport athletes, (3) had played or were currently playing individual or team sports, (4) played contact and non-contact sports, (5) played sports involving a ball and those that do not, (6) played sports where the outcome was determined by a score or the outcome of direct physical competition or subjectively by judges, or (7) were starters or reserves on their teams. However, women that played overhand throwing sports softball and water polo had significantly smaller digit ratios than did women that played other sports. These differences were not due to scaling effects. The independent samples t-test results were supported by subsequent Monte Carlo bootstrap, Bayesian, Random Forest, and multiple linear regression analyses. We suggest that the organizational consequences of prenatal testosterone exposure may influence the anatomy and physiology of women that leads to success playing overhand throwing sports.

The Second to Fourth Digit Ratio in Elite and Non-Elite Greco-Roman Wrestlers

A low second-to-fourth digit ratio (2D:4D) has been reported to correlate with high performance and athletic potential of an individual in sport. It has been suggested that 2D:4D is a relatively weak predictor of strength and a stronger predictor of efficiency in aerobic exercise. Comparing extreme groups on a continuum of sports performance requiring high power (physical strength) output would be helpful to resolve this issue. Therefore, the purpose of the present study was to compare the 2D:4D ratio of world-class elite Greco-Roman wrestlers (n = 10) taking part in Olympic fitness camps in 2013 with the 2D:4D ratio of non-elite collegiate wrestlers (n = 20), and age-matched sedentary males (n = 40). The 2D:4D ratios of elite wrestlers were lower compared to non-elite athletes (p < 0.01, right hand d = 1.70, left hand d = 1.67) and the control group (p < 0.0001, right hand d = 3.16, left hand d = 2.00). No significant differences were noted among the groups for right - left 2D:4D. We concluded that 2D:4D may discriminate between non-elite and world-class wrestlers. We also suggest that a low 2D:4D ratio could be linked to performance potential in wrestlers. As such, 2D:4D may provide additional information, which is valuable in determining the potential athleticism of an individual, when it is used in conjunction with other measures.

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.

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.

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.

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.

Putative Androgen Exposure and Sexual Orientation: Cross-Cultural Evidence Suggesting a Modified Neurohormonal Theory

INTRODUCTION

According to neurohormonal theory, prenatal androgens are key determinants of sexual orientation. As a reputed marker for prenatal androgens, the 2D:4D finger length ratio has been used in more than a dozen studies to test the hypothesis that prenatal androgens influence sexual orientation. Findings have been very inconsistent.

AIM

The present study sought to retest the hypothesis that 2D:4D and sexual orientation are related is a manner consistent with neurohormonal theory.

METHODS

A 2D:4D measure (of the right hand) along with four additional somatic markers of androgen exposure (height, physical strength, muscularity, and athletic ability) with samples of college students in Malaysia (N = 2,058) and the United States (N = 2,511). The five androgen measures were factor analyzed, resulting in a two-factor solution: Factor 1 consisted of strength, muscularity, and athletic ability (the muscular coordination factor), and Factor 2 was comprised of the r2D:4D and adult height (the bone growth factor).

MAIN OUTCOME MEASURES

Sexual orientation was measured by asking each respondent the extent to which they were sexually attracted to males and the extent to which they were sexually attracted to females, both on 11-point scales.

RESULTS

When the countries and sexes were analyzed separately, neither the r2D:4D measure nor Factor 2 correlated with sexual orientation to significant degrees. Instead, it was the muscular coordination factor that correlated the best. Support was found for the hypothesis that prenatal androgens influence sexual orientation, but the nature of these influences was more complex than neurohormonal theory predicted.

CONCLUSION

A modified theory is needed and presented to accommodate the results from this study.

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

BACKGROUND

The relative lengths of the index finger to the ring finger (2D:4D) is sexually dimorphic and is thought to be a correlate of prenatal sex steroids (low 2D:4D=high prenatal testosterone and low prenatal oestrogen). In adults there have been reports that low 2D:4D is consistently associated with high sports performance.

AIMS

To investigate correlations between 2D:4D and fitness levels in children.

STUDY DESIGN

Right 2D:4D and body size were measured, in addition to flexibility, speed, endurance and strength (Eurofit tests).

SUBJECTS

922 boys and 835 girls (mean ages (years): 10.8 ± 1.01 and 10.07 ± 1.00 respectively).

OUTCOME MEASURES

height, mass, BMI, triceps and subscapular skinfolds, 20 m shuttle run, sit and reach, standing broad jump, hand grip strength, 10 × 5m sprint, and the sit and reach test.

RESULTS

Boys significantly outperformed the girls in the 10 × 5m sprints, the 20 m shuttle run, standing broad jump, and hand grip strength. In boys but not girls, 2D:4D was significantly negatively correlated with scores in all these tests except the standing broad jump. In girls but not boys, 2D:4D was significantly positively correlated to stature, mass, BMI and waist circumference.

CONCLUSIONS

It is suggested that high prenatal testosterone and low prenatal oestrogen (low 2D:4D) is implicated in high sprinting speed, endurance and hand grip strength in boys. In girls low prenatal testosterone and high prenatal oestrogen is associated with large body size.

Physical strength and dance attractiveness: Further evidence for an association in men, but not in women

OBJECTIVES

Physical strength provides information about male quality and can be assessed from facial and body morphology. Research on perception of dance movements indicates that body movement also provides information about male physical strength. These relationships have not been investigated for women.

METHODS

We investigated relationships of handgrip strength (HGS) and dance attractiveness perception in 75 men and 84 women.

RESULTS

We identified positive relationships between HGS and opposite-sex assessments of dance attractiveness for men but not women.

CONCLUSIONS

The replication of previous research investigating relationships between dance attractiveness and physical strength in men corroborates the hypothesis that dance movements provide information about male quality. We argue that these relationships are interpretable in contexts of inter- and intra-sexual selection.

Aggressive-antisocial boys develop into physically strong young men

Young men with superior upper-body strength typically show a greater proclivity for physical aggression than their weaker male counterparts. The traditional interpretation of this phenomenon is that young men calibrate their attitudes and behaviors to their physical formidability. Physical strength is thus viewed as a causal antecedent of aggressive behavior. The present study is the first to examine this phenomenon within a developmental framework. We capitalized on the fact that physical strength is a male secondary sex characteristic. In two longitudinal cohorts of children, we estimated adolescent change in upper-body strength using the slope parameter from a latent growth model. We found that males' antisocial tendencies temporally precede their physical formidability. Boys, but not girls, with greater antisocial tendencies in childhood attained larger increases in physical strength between the ages of 11 and 17. These results support sexual selection theory, indicating an adaptive congruence between male-typical behavioral dispositions and subsequent physical masculinization during puberty.

Genetic influences on the development of grip strength in adolescence

Enhanced physical strength is a secondary sex characteristic in males. Sexual dimorphism in physical strength far exceeds sex differences in stature or total body mass, suggesting a legacy of intense sexual selection. Upper-body strength is a particularly promising marker of intrasexual competitiveness in young men. Consequently, it is assumed that sex-influenced gene expression contributes to the development of physical strength. It is unclear, however, whether the underlying sources of individual differences in strength development are comparable across sex. We obtained three measurements of hand-grip strength (HGS) over a six-year period spanning adolescence in male and female same-sex twins (N = 2,513). Biometrical latent growth models were used to partition the HGS variance at age 11 (intercept) and its growth over time (slope) into genetic and environmental components. Results demonstrated that variance around the intercept was highly heritable in both males and females (88% and 79%, respectively). In males, variance around the slope exceeded that of the intercept, while the reverse held for females. Additive genetic effects accounted for most (80%) of the variance around the slope in males, but were of less importance in females (heritability = 28%). Absolute genetic variance around the slope was nearly nine-fold higher in males. This striking disparity suggests that the developmental processes shaping HGS growth are different between the sexes. We propose that this might account for the sex-specific pattern of associations between HGS and external measures (e.g., digit ratio and physical aggression) typically reported in the literature. Our results underscore the role of endogenous androgenic influences in the development of physical strength.

Digit ratio (2D:4D) and handgrip strength in Hani ethnicity

Introduction

The ratio of the length of the second finger to the fourth finger (2D:4D) in humans is considered as a putative marker of prenatal exposure to testosterone, and has been progressively adopted as one useful tool to evaluate the effect of prenatal hormones in some traits such as physical ability. Handgrip strength is one authentic measure of physical ability and is generally used on the anthropological research within an evolutionary viewpoint.

Methods

Here we present the first evidence on 2D:4D and handgrip strength on adult participants of Hani ethnicity and explore the relationship between digit ratio (2D:4D) and handgrip strength. We examined 2D:4D and handgrip strength of 80 males and 60 females at Bubeng village, in the Yunnan province of China.

Results

The mean 2D:4D in females was higher than that in males for each hand. Females showed significantly higher 2D:4D than males in the right hand rather than in the left hand. Males displayed significantly higher handgrip strength than females for both hands. Handgrip strength decreased with age for both sexes. A significant negative correlation between 2D:4D and handgrip strength was found in the right hand of males.

Conclusion

The relationship between 2D:4D and handgrip strength may be attributed to evolutionary drive of sexual selection operating on fetal programming.

Reliability of a field based 2D:4D measurement technique in children

BACKGROUND

There is limited literature on the relationship between second to fourth finger digit ratio (2D:4D) and health- and skill-related fitness in children. To examine this relationship it is important to establish a reliable method of assessing 2D:4D for use with large groups of children.

AIM

The aim of the study was to examine the reliability of a field-based 2D:4D measure in children. METHODS/RESEARCH DESIGN: Fifty 8-11 year olds had 2D:4D of the right hand measured using a Perspex table top, a digital camera, and Adobe Photoshop software. Second to fourth finger digit ratio (and 2D and 4D) intra-observer and inter-observer reliabilities were assessed on the same day and intraobserver reliability was measured between days. Limits of agreement (LoA), coefficient of variation (CV) and Pearson's correlation coefficient were used for statistical analysis.

RESULTS

High correlation coefficients (r=0.95-0.99) and low CV's (0.4-1.2%) were reported for intra- and inter-observer reliabilities on the same day and between days. LoA revealed negligible systematic bias with random error ranging from 0.02 to 0.12.

CONCLUSION

These findings suggest that 2D:4D (and 2D and 4D) assessment in children using digital photography provides a reliable measure of 2D:4D that can be used during field-based testing.