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

The Use of Free Weight Squats in Sports: A Narrative Review-Squatting Movements, Adaptation, and Sports Performance: Physiological

ABSTRACT

Stone, MH, Hornsby, G, Mizuguchi, S, Sato, K, Gahreman, D, Duca, M, Carroll, K, Ramsey, MW, Stone, ME, and Haff, GG. The use of free weight squats in sports: a narrative review-squatting movements, adaptation, and sports performance: physiological. J Strength Cond Res 38(8): 1494-1508, 2024-The squat and its variants can provide numerous benefits including positively affecting sports performance and injury prevention, injury severity reduction, and rehabilitation. The positive benefits of squat are likely the result of training-induced neural alterations and mechanical and morphological adaptations in tendons, skeletal muscles, and bones, resulting in increased tissue stiffness and cross-sectional area (CSA). Although direct evidence is lacking, structural adaptations can also be expected to occur in ligaments. These adaptations are thought to beneficially increase force transmission and mechanical resistance (e.g., resistance to mechanical strain) and reduce the likelihood and severity of injuries. Adaptations such as these, also likely play an important role in rehabilitation, particularly for injuries that require restricted use or immobilization of body parts and thus lead to a consequential reduction in the CSA and alterations in the mechanical properties of tendons, skeletal muscles, and ligaments. Both volume and particularly intensity (e.g., levels of loading used) of training seem to be important for the mechanical and morphological adaptations for at least skeletal muscles, tendons, and bones. Therefore, the training intensity and volume used for the squat and its variations should progressively become greater while adhering to the concept of periodization and recognized training principles.

2D:4D-ratios among individuals with amphetamine use disorder, antisocial personality disorder and with both amphetamine use disorder and antisocial personality disorder

BACKGROUND

There is sufficient evidence that the index-finger-to-ring-finger-ratio (2D:4D-ratio) is associated with testosterone and estrogen exposure during the fetal stage. More specifically, a lower 2D:4D-ratio (that is; a shorter index finger, compared to a longer ring finger) was associated with a prenatally higher testosterone and lower estrogen exposure during the first trimester of the fetal stage. At a behavioral level, among adults, a lower 2D:4D-ratio was associated with a higher competitive performance among both female and male professional athletes, and with personality traits such as higher scores for mental toughness, dark triad traits, and aggressive behavior, and internet use disorder. Here, we tested, if 2D:4D-ratios differed among three clinical samples of individuals with amphetamine use disorder (AUD), antisocial personality disorder (ASPD), or both AUD and ASPD (AUD + ASPD), and when compared to healthy controls.

METHOD

The sample consisted of 44 individuals (mean age: 32.95 years; 22.7% females) diagnosed either with AUD (n = 25), ASPD (n = 10) or both AUD + ASPD (n = 9), and of 36 healthy controls (mean age: 23.28; 25% females). After a thorough clinical assessment, participants provided the scans of their right-hand palm to measure the lengths of their index finger and ring finger. Further, participants with AUD, ASPD and both AUD + ASPD completed a series of self-rating questionnaires on Dark Triad traits, narcissism sensitivity, and intolerance of uncertainty.

RESULTS

Compared to healthy controls, participants with AUD, ASPD, or AUD + ASPD showed statistically significantly lower 2D:4D-ratios. Participants with AUD + ASPD showed statistically significantly lowest 2D:4D-ratios, compared to participants with AUD and compared to healthy controls. For the clinical sample, a lower 2D:4D-ratio was associated with higher Dark Triad traits. 2D:4D-ratios were unrelated to narcissism sensitivity or intolerance of uncertainty. Higher scores for Dark Triad traits were associated with higher scores for narcissism sensitivity and intolerance of uncertainty.

CONCLUSIONS

Compared to healthy controls, individuals with amphetamine use disorder and concomitant antisocial personality disorder (AUD + ASPD) appeared to have been exposed to particularly high prenatal testosterone and particularly low estrogen concentrations, which, at a behavioral level, might have led to a fast life history for immediate resource acquisition.

Does maturity estimation, 2D:4D and training load measures explain physical fitness changes of youth football players?

OBJECTIVES

The purpose of the present study was two-fold: (1) To analyse physical fitness changes of youth football players after a full-season; and (2) to examine whether physical fitness changes are explainable by estimated maturity status, 2digit:4digit ratio (2D:4D) from each hand and training load (TL) measures.

METHODS

Twenty-seven youth elite Under-15 football players were daily monitored for training load measures during 38 weeks. At the beginning and at the end of the season, all players were assessed for physical fitness. Also, the maturity status estimation and the length of the second and fourth digits of both hands were collected at the beginning of the season.

RESULTS

Significant differences were found for all physical fitness measures after the season. The second and fourth digits of left and right hands had negative moderate correlations with change of direction (COD) changes (r=-.39 to - 0.45 | p = .05 to 0.02). Also, the maturity offset measure had negative moderate correlations with COD changes (r=-.40 | p = .04). From the reported significant correlations, the maturity offset, Left 4D, Right 2D and Right 4D significantly predicted the Mod.505 COD test changes (β = 0.41, p = .04; β = -0.41, p = .04; β = -0.45, p = .02; and β = -0.44, p = .03, respectively).

CONCLUSION

The maturity offset and the 2D:4D measures have the potential to predict COD performance changes over-time in youth football players. Given the lack of associations between the maturity estimation, 2D:4D and training load measures, with the overall physical fitness measures, coaches should rely only at COD changes.