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Human Movement Science Oct 2022In the referent control theory, grip force emerges by designating the referent aperture (R) as a threshold position inside the object. This study quantified R and...
In the referent control theory, grip force emerges by designating the referent aperture (R) as a threshold position inside the object. This study quantified R and investigated whether the synergistic control of digit referent coordinate (RC) and apparent stiffness (k) depend on the external mechanical constraints on the hand-held object. Subjects held a motorized handle capable of adjusting the grip width and performed static multi-digit prehension tasks in which the handle was free and externally fixed in different conditions. The RC and k of individual digits were reconstructed from the changes in digit normal forces and the positions as the grip width was modulated. RCs of the thumb and virtual finger were used to calculate the width and midpoint of R, and synergy indices quantifying the task-specific covariation in the space of the digit normal forces and {RC, k} variables were computed. We found that the k and width of the R were larger when holding a free handle than the fixed handle. The higher stiffness in the free condition could be a strategy to ensure grip stability. The midpoint of R was skewed toward the virtual finger, reflecting different magnitudes of k for the two digits. Further, the normal forces and control variables {RC, k} displayed synergistic covariation for stabilization of the total grasping force. Finally, the synergies were weaker when the handle was externally fixed, demonstrating the dependence of synergies on external constraints. These results add to the current literature by demonstrating that grasp control involves modulation of digit apparent stiffness in addition to the referent coordinate and by identifying the synergistic organization of the control variables during static grasp.
Topics: Fingers; Hand Strength; Humans; Movement; Psychomotor Performance; Thumb
PubMed: 35986961
DOI: 10.1016/j.humov.2022.102994 -
Regeneration (Oxford, England) Aug 2015A variety of digit and limb repair and reconstruction methods have been used in different clinical settings, but regeneration remains an item on every plastic surgeon's... (Review)
Review
A variety of digit and limb repair and reconstruction methods have been used in different clinical settings, but regeneration remains an item on every plastic surgeon's "wish list." Although surgical salvage techniques are continually being improved, unreplantable digits and limbs are still abundant. We comprehensively review the structural and functional salvage methods in clinical practice, from the peeling injuries of small distal fingertips to multisegmented amputated limbs, and the developmental and tissue engineering approaches for regenerating human digits and limbs in the laboratory. Although surgical techniques have forged ahead, there are still situations in which digits and limbs are unreplantable. Advances in the field are delineated, and the regeneration processes of salamander limbs, lizard tails, and mouse digits and each component of tissue engineering approaches for digit- and limb-building are discussed. Although the current technology is promising, there are many challenges in human digit and limb regeneration. We hope this review inspires research on the critical gap between clinical and basic science, and leads to more sophisticated digit and limb loss rescue and regeneration innovations.
PubMed: 27499873
DOI: 10.1002/reg2.41 -
Journal of Exercise Rehabilitation Dec 2016Second 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... (Review)
Review
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.
PubMed: 28119871
DOI: 10.12965/jer.1632862.431 -
Frontiers in Cell and Developmental... 2023Understanding the remarkable capacity of vertebrates to naturally regenerate injured body parts has great importance for potential translation into human therapeutic... (Review)
Review
Understanding the remarkable capacity of vertebrates to naturally regenerate injured body parts has great importance for potential translation into human therapeutic applications. As compared to other vertebrates, mammals have low regenerative capacity for composite tissues like the limb. However, some primates and rodents can regenerate the distal tips of their digits following amputation, indicating that at least very distal mammalian limb tissues are competent for innate regeneration. It follows that successful digit tip regenerative outcome is highly dependent on the location of the amputation; those proximal to the position of the nail organ do not regenerate and result in fibrosis. This distal regeneration proximal fibrosis duality of the mouse digit tip serves as a powerful model to investigate the driving factors in determining each process. In this review, we present the current understanding of distal digit tip regeneration in the context of cellular heterogeneity and the potential for different cell types to function as progenitor cells, in pro-regenerative signaling, or in moderating fibrosis. We then go on to discuss these themes in the context of what is known about proximal digit fibrosis, towards generating hypotheses for these distinct healing processes in the distal and proximal mouse digit.
PubMed: 37325560
DOI: 10.3389/fcell.2023.1217185 -
The International Journal of... 2018The distal part of the tetrapod limb, the autopod, is characterized by the presence of digits. The digits display a wide diversity of shapes and number reflecting... (Review)
Review
The distal part of the tetrapod limb, the autopod, is characterized by the presence of digits. The digits display a wide diversity of shapes and number reflecting selection pressure for functional adaptation. Despite extensive study, the different aspects of digit patterning, as well as the factors and mechanisms involved are not completely understood. Here, we review the evidence implicating Hox proteins in digit patterning and the interaction between Hox genes and the Sonic hedgehog/Gli3 pathway, the other major regulator of digit number and identity. Currently, it is well accepted that a self-organizing Turing-type mechanism underlies digit patterning, this being understood as the establishment of an iterative arrangement of digit/interdigit in the hand plate. We also discuss the involvement of 5' Hox genes in regulating digit spacing in the digital plate and therefore the number of digits formed in this self-organizing system.
Topics: Animals; Body Patterning; Extremities; Gene Expression Regulation, Developmental; Genes, Homeobox; Hedgehog Proteins; Signal Transduction
PubMed: 30604849
DOI: 10.1387/ijdb.180200mr