Evaluation of the relationship between the 2D:4D ratio, fine hand motor skills, and anatomy practical examination performance in first-year medical students

Abstract

Background

The second-to-fourth digit ratio (2D:4D) has been proposed as a morphometric marker of prenatal androgen exposure and has been linked to cognitive and behavioral traits. This study aimed to investigate the relationship between the 2D:4D ratio, fine hand motor skills, and practical anatomy examination performance among first-year medical students.

Methods

This cross-sectional study included voluntary first-year medical students at Kocaeli University Faculty of Medicine. The lengths of the second (2D) and fourth (4D) fingers of the right hand were measured using a digital caliper, and the 2D:4D ratio was calculated. Fine hand motor performance was assessed using the Nine-Hole Peg Test (NHPT). Practical anatomy examination scores were used to determine practical examination performance. Students with an average score above 65 were classified as successful.

Results

Correlation analysis showed a weak but statistically significant negative association between NHPT duration and practical anatomy examination performance (ρ = -0.21, p = 0.043). Female students achieved significantly higher mean practical examination scores than males (p = 0.044). No significant correlation was found between the 2D:4D ratio and practical examination performance (ρ = 0.02, p = 0.854). Successful students completed the NHPT in significantly shorter time than their peers (p = 0.016).

Conclusion

Fine hand motor skills performance was significantly associated with practical examination success, whereas no significant association was observed between the 2D:4D ratio and examination performance. Future studies should further investigate the influence of sex, question type, way of flagging, and time constraints in anatomy practical examinations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12909-026-08617-w.

Introduction

Anatomy education is a fundamental component of medical curricula and plays a critical role in shaping the professional development of future physicians. Its instruction requires comprehension of three-dimensional structures, spatial perception, visual memory, and higher-order cognitive processes [1–3]. Practical anatomy examinations aim to assess students’ abilities to localize, identify, and interpret the function of morphological structures. In this process, individual differences in attention, memory, and psychomotor competence may significantly influence student success [4]. The development and measurement of spatial ability have also been emphasized in educational contexts [5].

The Mental Rotation Test (MRT) is widely recognized as a robust measure of spatial ability and has been extensively applied in anatomy education research [6, 7]. The 2D:4D ratio- the proportion between the lengths of the second and fourth fingers has been proposed as a biological marker of prenatal androgen exposure. It has been linked to various cognitive, behavioral, and physical traits [8–10]. Several studies have examined the relationship between the 2D:4D ratio and academic performance, mathematical reasoning, musical ability, leadership, and risk-taking behavior [11–13]. However, consistent results in educational contexts remain elusive.

The Nine-Hole Peg Test (NHPT) is widely used to assess visuomotor coordination and fine motor skills. It is a standard tool for evaluating upper extremity function, particularly in the diagnosis and monitoring of neurological conditions [14, 15]. Recently, it has also been applied to assess psychomotor performance in medical education [16–18]. Computer-based and traditional methods have shown variable effects on anatomy learning, with spatial visualization identified as a major contributor to performance [19]. Moreover, technical and motor skills in healthcare have been shown to correlate with psychomotor and cognitive factors, including spatial ability [20].

This study aimed to evaluate the relationship between the 2D:4D digit ratio and hand motor performance with practical anatomy examination success among first-year medical students. Practical anatomy examinations require rapid visual discrimination of structures, interpretation of three-dimensional spatial relationships, and efficient visuomotor coordination during time-limited station transitions. Therefore, both cognitive spatial processing and psychomotor performance may influence examination outcomes. The 2D:4D ratio has been associated with spatial ability and visuospatial reasoning, whereas motor performance assessed by the NHPT reflects fine motor coordination and visuomotor integration. Considering that anatomy practical assessments rely primarily on identifying and localizing structures rather than verbal reasoning or complex problem-solving, combining morphometric (2D:4D) and psychomotor (NHPT) measures provides an integrated framework for understanding individual differences in anatomy learning. Based on this conceptual rationale, it was hypothesized that a lower 2D:4D ratio and better hand motor performance would be associated with higher practical anatomy examination scores.

Methods

This cross-sectional study was conducted at Kocaeli University Faculty of Medicine among first-year medical students who voluntarily participated. The relationship between students’ practical anatomy examination performance and their finger morphometric characteristics and find hand motor skills was investigated. An a priori power analysis was performed using G*Power 3.1.9.7 to estimate the minimum sample size required for correlation analysis. Based on the total number of first-year medical students enrolled at Kocaeli University Faculty of Medicine (N ≈ 250) and assuming a medium effect size (ρ = 0.30), an alpha level of 0.05, and 80% statistical power, the analysis indicated that at least 84 participants were required. A total of 94 voluntary participants were ultimately included, exceeding this minimum requirement.

Participants were recruited on a voluntary basis from first-year medical students through announcements made during scheduled anatomy laboratory sessions. All students enrolled in the course were invited to participate. Inclusion criteria consisted of being a first-year medical student and completing the practical anatomy examination. Exclusion criteria included a history of upper-limb trauma, neurological or musculoskeletal disorders that could impair fine hand motor skills, or any condition known to influence NHPT performance. Dominant hand information was not collected, and therefore hand dominance was not used as a selection criterion. All students received verbal and written information about the study procedures, and written informed consent was obtained prior to participation in accordance with institutional ethical approval.

The study was conducted during the 2024–2025 academic year. Participant characteristics, including sex, age, height, weight, and BMI (body mass index), were recorded for each student. Height and body weight were measured by the researchers using a calibrated stadiometer and digital scale with participants wearing light clothing and no shoes. Body mass index was calculated as weight in kilograms divided by height in meters squared (kg/m²). The measurement procedure was standardized through a preliminary calibration study involving 20 participants, during which each measurement was performed twice by two trained investigators, yielding excellent inter-rater reliability (ICC = 0.914, 95% CI: 0.78–0.96). To minimize measurement error, all subsequent digit-length measurements were performed once per participant under the same standardized laboratory conditions, using the same calibrated digital caliper and by the same two investigators. The practical anatomy examination was conducted in a silent environment, with students rotating individually between stations to minimize bias and ensure consistent testing conditions.

Practical anatomy examinations were conducted in two separate modules (the fifth and sixth module assessments). Each assessment consisted of five stations, and each station included two questions, resulting in a total of 10 questions per examination. Each station displayed cadaveric specimens, prosected anatomical pieces, or anatomical models, with a colored pin marking a specific anatomical structure. Students were required to write the anatomical name of each pinned structure on an answer sheet. Each correct answer was scored with 10 points, for a total of 100 points per examination. Students were allowed 50 s per station and 10 s for transition, without any haptic component.

The fifth module focused on skeletal and tissue systems, whereas the sixth module covered muscular system. The same timing, scoring, and station-based format were applied in both modules. For the analyses, the mean score of the two examinations was used as the practical anatomy performance variable. A complete list of station topics is provided in Supplementary Material 1.

All measurements (2D:4D ratio and NHPT) were performed during the week following the second (sixth module) practical anatomy examination, during scheduled anatomy laboratory sessions. This timing ensured that data collection did not interfere with examination preparation and allowed all participants to be assessed under standardized post-examination conditions.

Finger morphometry was assessed by measuring the lengths of the second (index) and fourth (ring) digits of the right hand using a digital caliper with 0.001 mm precision. Measurements were taken on the palmar surface from the midpoint of the proximal digital crease to the distal tip of each finger, following standard soft-tissue measurement protocols described in previous anatomical and behavioral studies [21, 22]. All measurements were obtained with the hand fully extended and supinated on a flat surface to ensure consistency. The 2D:4D ratio was calculated by dividing the length of the second digit by the length of the fourth digit. The right hand was selected because previous research indicates that right-hand 2D:4D values exhibit a larger sex difference and may be more sensitive to prenatal androgen exposure than the left hand [21, 23].

Hand motor performance was assessed using the NHPT, a standardized measure of fine motor coordination [14, 17]. The NHPT apparatus consisted of a wooden board with nine holes and nine pegs. Participants performed the test with their dominant hand, as verified by self-report. Each participant was asked to place and remove nine pegs as quickly as possible following a standardized sequence demonstrated before the trial. The duration required to complete the task was recorded in seconds using a digital stopwatch. Each participant performed a single trial to minimize fatigue and ensure consistency, in accordance with previous educational and behavioral studies using the NHPT [24].

For between-group comparisons, practical anatomy examination performance was operationalized as follows: students with an average score above 65 were categorized as ‘successful’, whereas those scoring below 65 were categorized as ‘unsuccessful’.

Statistical analysis

All statistical analyses were performed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA). Normality of continuous variables was assessed using the Shapiro-Wilk test. Continuous variables were presented as mean ± standard deviation (SD). Variables that met normality assumptions were analyzed using parametric tests (Student’s t-test for group comparisons and Pearson correlation for associations), whereas non-normally distributed variables were evaluated using non-parametric alternatives (Mann-Whitney U test and Spearman rank correlation). Discrete variables were described as frequency (n) and percent (%) with group comparisons performed using Fisher’s exact test. A p-value < 0.05 was considered statistically significant.

Results

A total of 94 students participated in the study, including both male and female students. The mean age was 19.04 ± 1.10 years. Male students had significantly higher height, weight, and BMI compared to female students (p < 0.001) (Table 1).

Table 1.

Descriptive characteristics of participants by sex

Variable	Female (n = 30)	Male (n = 64)	Total (n = 94)	p-value
Age	19.27 ± 1.23	18.94 ± 1.03	19.04 ± 1.10	0.238 b
Height (cm)	166.43 ± 5.25	179.67 ± 6.83	175.40 ± 8.88	< 0.001 a
Weight (kg)	59.63 ± 10.00	79.43 ± 14.70	73.04 ± 16.24	< 0.001 b
BMI (kg/m²)	21.49 ± 3.07	24.56 ± 3.95	23.57 ± 3.95	< 0.001 b
2D length (mm)	63.83 ± 5.05	70.64 ± 4.72	68.44 ± 5.77	< 0.001 a
4D length (mm)	64.31 ± 5.12	71.11 ± 4.62	68.92 ± 5.73	< 0.001 a
2D:4D ratio	0.99 ± 0.03	0.98 ± 0.02	0.98 ± 0.02	0.026 b
Practical anatomy examination score (0-100)	69.25 ± 20.33	59.80 ± 21.33	62.85 ± 21.37	0.044 a
NHPT duration (sec)	18.78 ± 2.30	20.06 ± 3.02	19.65 ± 2.86	0.080 b

Values are presented as mean ± standard deviation (SD)

a = Student’s t-test (parametric variables); b = Mann-Whitney U test (non-parametric variables)

Abbreviations: n frequency, p statistical significance, kg kilogram, m meter, mm millimeter, cm centimeters, BMI body mass index, NHPT Nine-Hole Peg Test, 2D:4D second-to-fourth digit ratio

Table 1 summarizes the descriptive characteristics of the participants by sex, demonstrating consistent anthropometric differences favoring males in height, weight, and BMI.

Finger length measurements indicated that males had significantly longer 2D and 4D digits compared to females (p < 0.001). The mean 2D:4D ratio was 0.99 ± 0.03 for females and 0.98 ± 0.02 for males, a difference that was statistically significant (p = 0.026) (Fig. 1).

Fig. 1.

Sex differences in 2D:4D ratio and practical anatomy examination score. Abbreviations: 2D:4D, second-to-fourth digit ratio; p, statistical significance, (a) shows a significantly higher 2D:4D ratio in female students compared with male students (p = 0.026), while (b) shows significantly higher practical anatomy examination scores among female students than male students (p = 0.044).

Figure 1 illustrates the sex-based differences in both 2D:4D ratio and practical anatomy examination score, highlighting a slightly higher digit ratio and better examination performance among female students.

Regarding practical anatomy examination performance, female students achieved significantly higher mean scores than male students (p = 0.044), while NHPT durations were shorter in the successful group compared to the unsuccessful group, indicating better hand motor performance among higher-performing students (p = 0.016) (Table 2; Fig. 2).

Table 2.

Comparison of 2D:4D ratio and NHPT duration by practical examination success

Variable	Unsuccessful (n = 39)	Successful (n = 54)	p-value
2D:4D ratio (Female)	1.00 ± 0.03	0.99 ± 0.02	0.519 a
2D:4D ratio (Male)	0.98 ± 0.02	0.98 ± 0.02	0.752 b
2D:4D ratio (Total)	0.98 ± 0.02	0.99 ± 0.02	0.947 a
NHPT duration (Female)	19.56 ± 2.25	18.39 ± 2.28	0.193 a
NHPT duration (Male)	20.96 ± 3.29	19.30 ± 2.57	0.048 b
NHPT duration (Total)	20.60 ± 3.09	18.96 ± 2.49	0.016 b

Values are presented as mean ± standard deviation (SD)

a = Student’s t-test (parametric variables); b = Mann-Whitney U test (non-parametric variables)

Abbreviations: n frequency, p statistical significance, NHPT Nine-Hole Peg Test, 2D:4D second-to-fourth digit ratio

Fig. 2.

Comparison of 2D:4D ratio and NHPT duration between successful and unsuccessful students. Abbreviations: 2D:4D, second-to-fourth digit ratio; NHPT, Nine-Hole Peg Test; p, statistical significance, (a) shows no significant difference in the 2D:4D ratio between successful and unsuccessful students (p = 0.947), whereas (b) shows significantly shorter NHPT duration among successful students compared with unsuccessful students (p = 0.016).

Table 2 details these comparisons, and Fig. 2 visually demonstrates that the successful group exhibited shorter NHPT durations, reflecting greater fine hand motor skills.

A weak but statistically significant negative correlation was found between NHPT duration and practical anatomy examination performance (ρ = -0.21, p = 0.043), as shown in Fig.3

Fig. 3.

Relationship of NHPT duration and 2D:4D ratio with practical anatomy examination scores. Abbreviations: NHPT, Nine-Hole Peg Test; 2D:4D, second-to-fourth digit ratio; ρ, Spearman’s rank correlation coefficient; p, statistical significance, (a). In contrast, no significant association was observed between the 2D:4D ratio and examination performance (Spearman’s ρ = 0.02, p = 0.854), as displayed in (b) and summarized in Table 3. Figure 3(a) demonstrates the inverse trend between NHPT completion time and anatomy examination score.

Table 3.

Spearman correlation analysis of the relationship between NHPT duration, 2D:4D ratio, and anatomy examination performance

Variable	Spearman’s ρ	p-value	n
NHPT duration	-0.21	0.043	94
2D:4D ratio	0.02	0.854	94

Non-parametric Spearman’s rank correlation coefficient (ρ) and corresponding p-values are reported

Abbreviations: n frequency, p statistical significance, ρ Spearman’s rank correlation coefficient, NHPT Nine-Hole Peg Test, 2D:4D second-to-fourth digit ratio

Discussion

This study explored the relationship between finger morphometry (2D:4D ratio) and hand motor performance (NHPT duration) with practical anatomy examination success among first-year medical students. Findings revealed no significant association between 2D:4D ratio and practical anatomy examination performance, while fine hand motor skills demonstrated a significant negative correlation with examination success based on non-parametric Spearman analysis.

The absence of a significant relationship between 2D:4D and academic performance aligns with the findings of Nye et al. (2012), who reported a nonlinear association moderated by sex and geographic factors [25]. Similarly, Güçlü et al. (2021) found no significant correlation between 2D:4D and academic performance among health science students [26]. While several studies have reported associations between 2D:4D and cognitive abilities, such findings often have small effect sizes and lack consistency across populations [12]. Spatial ability, which involves mental rotation, visualization, and manipulation of three-dimensional structures, plays a well-documented role in gross anatomy learning [27, 28]. Prior research has suggested that lower 2D:4D, indicative of higher prenatal androgen exposure, may be associated with enhanced spatial ability and indirectly with improved anatomy performance [19, 29–33]. However, the present study did not assess spatial ability using the MRT, focusing instead on psychomotor performance through the Nine-Hole Peg Test. Therefore, the lack of correlation between 2D:4D and anatomy examination performance may reflect that the examination emphasized recognition and localization of structures rather than spatial transformation.

Conversely, the significant negative relationship observed between NHPT duration and anatomy examination success is consistent with previous literature indicating that fine motor skills and visuomotor coordination contribute to improved performance in hands-on medical education environments. Jebakani et al. (2017) reported that students with better fine hand motor skills performed better in practical components of medical curricula [18]. NHPT performance has also been linked to short-term procedural success in both clinical and normative settings [34]. The NHPT primarily assesses fine motor coordination, visuomotor integration, and temporal precision, reflecting basic psychomotor abilities. In contrast, tests such as the Purdue Pegboard assess more complex manual proficiency, including bimanual coordination and sequential assembly [35]. Additionally, recent findings by Ulupınar et al. (2024) demonstrated that fine motor performance assessed through functional hand tests is strongly associated with perceived exertion and task efficiency, further supporting the relevance of evaluating basic motor skills such as the NHPT in educational and clinical contexts [24].

In this study, each participant’s NHPT completion time served as an indicator of fine hand motor skills. The anatomy practical examination required rapid visual identification of structures on cadaveric or prosected specimens within fixed time intervals (50 s per station), without any haptic component. Thus, the observed correlation likely reflects the contribution of visuomotor coordination and psychomotor efficiency rather than spatial transformation or tactile feedback abilities. Previous studies have emphasized the interconnectedness of spatial and manual competencies in anatomical learning [20, 36–38], supporting the notion that refined motor coordination may complement spatial cognition during anatomy education.

Sex differences in 2D:4D ratios observed in this study, with females demonstrating higher values than males, are consistent with established patterns of sexual dimorphism [26]. Female students in the present cohort also scored higher on the practical anatomy examination. However, prior literature has shown male advantages in spatial ability (e.g., MRT performance) and, in some contexts, in anatomy practical examinations [39–44]. Given that the practical examination in the present study emphasized rapid visual identification rather than haptic or spatial transformation tasks, the relationship between shorter NHPT duration and higher performance may represent the role of visuomotor efficiency rather than sex-linked spatial ability differences. The direction of sex differences in anatomy performance may vary depending on whether the task relies more heavily on visuomotor coordination versus spatial transformation, as well as on complexity and cohort characteristics.

The observed sex differences in NHPT duration and practical examination performance warrant further consideration in the context of spatial and visuomotor abilities. Although female students achieved slightly higher mean scores in the practical anatomy examination, this difference may reflect psychomotor efficiency rather than spatial ability. The examination primarily required rapid visual identification and factual recall, with minimal involvement of complex mental rotation or spatial transformation. Prior studies have shown that spatial ability and imagery style vary between individuals and may contribute to performance differences depending on task demands. Specifically, males are often reported to adopt spatial schematic strategies that favor abstract, flexible, and field independent manipulation of mental images, whereas females tend to use object visual strategies characterized by more detailed and concrete representations [45–47]. These cognitive preferences can influence task-specific performance, such that females may perform better in tasks emphasizing accuracy and perceptual attention, such as rapid visual identification, while males may show advantages in tasks requiring three-dimensional spatial manipulation. Moreover, Peters demonstrated that time constraints accentuate male advantages in spatial transformation tasks, suggesting that sex-related performance differences are context-dependent. In the present study, the time-limited nature of the practical anatomy examination may have favored visuomotor efficiency and attention to visual details rather than spatial reasoning, thereby accounting for the observed female advantage [48].

It is also noteworthy that anatomical structures in the practical examinations were marked using colored pins. Visual cues such as color may preferentially engage object visual strategies, which rely on detailed, pictorial representations of objects, rather than spatial schematic strategies that emphasize abstract, relational, and structural processing. In contrast, practical examinations in which structures are indicated using uncolored strings or ropes may place greater demands on spatial schematic processing, as students must rely more heavily on spatial relationships and three-dimensional organization rather than salient visual features. This distinction may partly contribute to task-specific and sex-related differences in practical anatomy performance, and it suggests that the method of flagging anatomical structures may influence the cognitive strategies employed by students during practical examinations.

Given the cognitive and psychomotor demands of anatomy education, motor skills may influence learning outcomes alongside cognitive capabilities. Previous work has shown that structured observation, checklist-based assessments, and deliberate practice can promote psychomotor competence in anatomy instruction [49]. An integrative review in undergraduate nursing education also emphasized the value of simulation, technology-enhanced learning, and repetitive training in improving motor performance [50].

It is important to emphasize that the scientific validity of the 2D:4D ratio as a biomarker remains debated. Although some studies have reported associations between 2D:4D and academic or cognitive performance [51, 52], others have highlighted inconsistent replication and small effect sizes across different populations [53, 54]. Moreover, recent work suggests that the relationship between 2D:4D and cognitive or motor outcomes may depend on contextual, cultural, or task-specific factors [55]. Given this variability, interpretations of 2D:4D findings in educational settings should be made with caution.

Overall, this study contributes to the understanding of the multidimensional nature of anatomy learning and highlights the relevance of psychomotor skill assessment in practical anatomy education.

Limitations

This study has several limitations. Its cross-sectional design prevents causal inference. The single-center setting and limited sample size may affect the generalizability of the findings. All measurements were performed within a single session, which may limit the evaluation of intra-individual variability. Handedness was not recorded, although participants performed the NHPT with their dominant hand, and this could have influenced motor performance or anatomical task execution. Additionally, the 2D:4D ratio was measured only on the right hand, and bilateral digit measurements were not collected, which limits interpretation of potential left and right asymmetry in digit ratio. Furthermore, spatial ability was not directly assessed using a standardized measure such as the MRT, which may have provided additional insight into visuospatial contributions to anatomy learning.

Future longitudinal and multicenter studies with larger and more diverse samples are warranted to further explore the role of morphometric and psychomotor factors in practical anatomy examination performance. The potential use of such markers in academic support and individualized educational strategies also merits further investigation.

Conclusion

This study examined the relationship between finger morphometry (2D:4D ratio) and hand motor performance (NHPT duration) with anatomy practical examination success in first-year medical students. Findings demonstrated that hand motor performance was significantly associated with practical anatomy examination success, whereas the 2D:4D ratio was not.

Although female students demonstrated slightly higher mean scores in both the NHPT and practical anatomy examinations, this difference may reflect visuomotor efficiency under time-limited conditions rather than sex-related spatial ability. These findings suggest that fine hand motor skills can influence practical anatomy performance, particularly in assessments emphasizing rapid visual identification.

Future research should further investigate the influence of sex, question type, and time constraints on practical anatomy performance, as well as explore educational strategies that promote psychomotor proficiency in medical students.

Authors’ contributions

A.O. and H.Y. conceived and designed the study. A.O. supervised the overall project. Both authors collected the data and contributed to the analysis and interpretation of the findings. A.O. and H.Y. conducted the literature review and drafted the manuscript. A.O. critically revised the final version. All authors read and approved the final manuscript.

Funding

This research was supported by the Scientific and Technological Research Council of Türkiye (TÜBİTAK) under the 2209-A Research Project Support Program for University Students (Project No: 1919B012466641).

Data availability

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Non-Interventional Clinical Research Ethics Committee of Kocaeli University Faculty of Medicine (Approval No: GOKAEK-2025/11/19, Project no: 2025/261) and was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all participants prior to data collection.

Consent for publication

Not applicable. This manuscript does not include any individual data, images, or details that could identify participants.

Competing interests

The authors declare no competing interests.