Relationship Between 2D:4D Finger Ratio and Proprioception

Background: 2D:4D ratio (the ratio of the length of the second digit to the length of the fourth digit) has been reported to be associated with muscle strength and physical performance, numerical competencies, spatial skills and cognitive abilities. However, the relationship between 2D:4D ratio and proprioception is not well-known, which was therefore aimed at investigating in current study. Methods: 2D:4D ratio (electronic digital calliper) and proprioception (Join position error is measure with Cervical Range of Motion instrument) were assessed in all individuals (n=35.7 ± 11.2 years).

2nd (index) and 4th (ring) finger ratio, index finger (2nd finger) length to ring divided by the length of the fourth finger (4th finger) and is referred to in the literature as the "2D:4D ratio". The reference points for 2D:4D ratio measurement are the midpoint of the proximal ventral flexion bend of the finger and the distal end of the finger. 2D:4D ratio is a function of prenatal exposure to testosterone and estrogen levels and shows gender-related differences. A low 2D:4D ratio indicates that prenatal testosterone levels are high and estrogen levels are lower, while a high 2D:4D ratio indicates lower testosterone and higher estrogen exposure. For example, men's index fingers (2D) are longer than their ring fingers (4D), while in women the second finger is usually significantly shorter than or slightly shorter than or equal to the fourth finger. In recent years, several studies have been conducted on the biological and behavioral associations with the 2D:4D ratio. For example, a low 2D:4D ratio is often associated with increased physical strength, athletic performance, and risk-taking behavior, while a high 2D:4D ratio is associated with traits such as empathy and language skills. Proprioception, which refers to the ability to sense joint and body movement, as well as the movement of the body or body segments, is defined as the perception of its position in space. Proprioception plays a critical role for balance, coordination, and motor control. The 2D:4D ratio, influenced by hormonal changes, may affect proprioceptive functions, such as motor skills and hand-eye coordination. Some studies have found that individuals with low 2D:4D ratios perform better on tasks involving mental rotation of two- and three-dimensional objects. Testosterone exposure during the prenatal period is thought to increase the development of the right hemisphere of the brain. Proprioception, a person's ability to perceive body position and movements, can also be significantly influenced by the 2D:4D ratio. The ratio is influenced by both genetic factors and prenatal environmental influences. For example, human tool manipulation in the course of evolution contributed to the differentiation and specialization of brain areas associated with sensory and motor skills. Some research suggests that a low 2D:4D ratio may be linked to stronger motor skills and a better proprioceptive sense. This is because prenatal testosterone levels affect motor control and nervous system development, influencing hand-eye coordination. For example, individuals with a low 2D:4D ratio may show improved hand-eye coordination and performance in tasks requiring fine motor control. A study examined the relationship between hand morphometry (including 2D:4D ratio) and proprioception and found that haptic perception was closely related to proprioception. Lower 2D:4D ratios were associated with better physical strength and precise motor control. Additionally, lower 2D:4D ratios have shown an association with better arithmetic, visual, and spatial skills. However, there are no available studies that directly address the relationship between proprioception and the 2D:4D ratio. Therefore, more research is needed to understand the connection between proprioception and 2D:4D ratio. The aim of this study is to investigate the relationship between the 2D:4D ratio and proprioception in adult subjects.

Eligibility Criteria:
Inclusion Criteria:

* Age between 18 and 65 years
* Agreeing to participate in the study.

Exclusion Criteria:

* Individuals who have scars, finger deformities, and/or surgical interventions that would prevent accurate measurement of the 2D:4D ratio
* Congenital hand anomalies
* History of trauma involving the hand or cervical region were excluded from the study.
* Having sensory loss or severe neurological disorder that would affect proprioception