Finger force sharing during an adapted power grip task

Deficits in force production during multifinger tasks demarcate cognitive dysfunction

BACKGROUND

The multifinger force deficit (MFFD) is the decline in force generated by each finger as the number of fingers contributing to an action is increased. It has been shown to associate with cognitive status.

AIMS

The aim was to establish whether a particularly challenging form of multifinger grip dynamometry, that provides minimal tactile feedback via cutaneous receptors and requires active compensation for reaction forces, will yield an MFFD that is more sensitive to cognitive status.

METHODS

Associations between measures of motor function, and cognitive status (Montreal Cognitive Assessment [MoCA]) and latent components of cognitive function (derived from 11 tests using principal component analysis), were estimated cross-sectionally using generalized partial rank correlations. The participants (n  =  62) were community dwelling, aged 65-87.

RESULTS

Approximately half the participants were unable to complete the dynamometry task successfully. Cognitive status demarcated individuals who could perform the task from those who could not. Among those who complied with the task requirements, the MFFD was negatively correlated with MoCA scores-those with the highest MoCA scores tended to exhibit the smallest deficits, and vice versa. There were corresponding associations with latent components of cognitive function.

DISCUSSION

The results support the view that neurodegenerative processes that are a feature of normal and pathological aging exert corresponding effects on expressions of motor coordination-in multifinger tasks, and cognitive sufficiency, due to their dependence on shared neural systems.

CONCLUSIONS

The outcomes add weight to the assertion that deficits in force production during multifinger tasks are sensitive to cognitive dysfunction.

Cortical bone distribution of the proximal phalanges in great apes: implications for reconstructing manual behaviours

Primate fingers are typically in direct contact with the environment during both locomotion and manipulation, and aspects of external phalangeal morphology are known to reflect differences in hand use. Since bone is a living tissue that can adapt in response to loading through life, the internal bone architecture of the manual phalanges should also reflect differences in manual behaviours. Here, we use the R package Morphomap to analyse high-resolution microCT scans of hominid proximal phalanges of digits 2-5 to determine whether cortical bone structure reflects variation in manual behaviours between bipedal (Homo), knuckle-walking (Gorilla, Pan) and suspensory (Pongo) taxa. We test the hypothesis that relative cortical bone distribution patterns and cross-sectional geometric properties will differ both among extant great apes and across the four digits due to locomotor and postural differences. Results indicate that cortical bone structure reflects the varied hand postures employed by each taxon. The phalangeal cortices of Pongo are significantly thinner and have weaker cross-sectional properties relative to the African apes, yet thick cortical bone under their flexor sheath ridges corresponds with predicted loading during flexed finger grips. Knuckle-walking African apes have even thicker cortical bone under the flexor sheath ridges, as well as in the region proximal to the trochlea, but Pan also has thicker diaphyseal cortices than Gorilla. Humans display a distinct pattern of distodorsal thickening, as well as relatively thin cortices, which may reflect the lack of phalangeal curvature combined with frequent use of flexed fingered hand grips during manipulation. Within each taxon, digits 2-5 have a similar cortical distribution in Pongo, Gorilla and, unexpectedly, Homo, which suggest similar loading of all fingers during habitual locomotion or hand use. In Pan, however, cortical thickness differs between the fingers, potentially reflecting differential loading during knuckle-walking. Inter- and intra-generic variation in phalangeal cortical bone structure reflects differences in manual behaviours, offering a comparative framework for reconstructing hand use in fossil hominins.

Human thumb consists of three phalanges and lacks metacarpal? A morphometric study on the long bones of the hand

PURPOSE

For many years, it was thought that the thumb consists of just two phalanges that differentiate it from the other four medial triphalangeal fingers. But there are some old reports that few former scientists believed the thumb has three phalanges and it lacked a metacarpal, and the thumb metacarpal is a phalanx. So this anthropometric study was carried out by investigating the morphology of the long bones of the hand and correlations between the thumb metacarpal and other miniature long bones of the hand.

METHODS

We studied anterior-posterior X-ray images of the right hands of 80 individuals from 18 to 65 years old. The exploration targets were the length of all metacarpals (MC), proximal phalanges (PP), middle phalanges (MP), and distal phalanges (DP). Friedman Repeated Measures Analysis of Variance and Dunn's post hoc test were carried out to compare the means of all variables. The correlation between all quantitative factors was done by Spearman Rank Correlation (Spearman's Rho) coefficient.

RESULTS

Our results showed that the length of the phalanges and the total length of the fingers are independent of the related metacarpal length (P < 0.001). Also, the thumb metacarpal length in comparison to all bones of the hand was significantly different from all long bones of the hand except the proximal phalanx of the middle finger (P = 1).

CONCLUSION

Based on the morphology of the long bones of the hand and the high similarity between the thumb metacarpal and phalanges especially the proximal phalanx of the middle finger, it can be suggested that the current thumb metacarpal is a proximal phalanx of the thumb.

Dynamical Synergies of Multidigit Hand Prehension

Hand prehension requires highly coordinated control of contact forces. The high-dimensional sensorimotor system of the human hand operates at ease, but poses several challenges when replicated in artificial hands. This paper investigates how the dynamical synergies, coordinated spatiotemporal patterns of contact forces, contribute to the hand grasp, and whether they could potentially capture the force primitives in a low-dimensional space. Ten right-handed subjects were recruited to grasp and hold mass-varied objects. The contact forces during this multidigit prehension were recorded using an instrumented grip glove. The dynamical synergies were derived using principal component analysis (PCA). The contact force patterns during the grasps were reconstructed using the first few synergies. The significance of the dynamical synergies, the influence of load forces and task configurations on the synergies were explained. This study also discussed the contribution of biomechanical constraints on the first few synergies and the current challenges and possible applications of the dynamical synergies in the design and control of exoskeletons. The integration of the dynamical synergies into exoskeletons will be realized in the near future.

Features of Index-Ring Finger Pair’s Force Contribution in Multi-Finger Force-Following Tasks

New types of cylindrical handles such as pushrims with force signal sensors under four fingers (excluding the thumb) enable real-time gripping-status assessment. The mirrored change phenomenon of the index and ring fingers observed in linear grip tasks offers a new perspective on finger grouping. To evaluate the force contribution of index-ring finger pair in multi-finger force, 10 right-handed male participants with similar hand sizes were recruited to participate in sinusoidal function force-following tasks involving a cylindrical handle. The real-time signal of the grip force and individual finger force were recorded to analyze real-time changes in the finger force contribution (FC). Subsequently, the time-FC curves of individual and paired fingers were analyzed. Results show are as follows: (1) When the FC of the index-ring finger pair exceeded that of the middle-little finger pair, the gripping load was relatively low, and a smaller difference between the FCs of the index-ring finger pair and the middle-little finger pair indicated a smaller following error. (2) The FC of index-ring finger pair is a better (higher-linearity) parameter to assess gripping status. These findings show that the paired-finger FC is an adequate parameter for the gripping-status assessment.

Complex couplings between joints, muscles and performance: the role of the wrist in grasping

The relationship between posture, muscle length properties and performance remains unclear, because of a lack of quantitative data. Studies on grasping tasks suggested that wrist position could favour the extrinsic finger flexor in regards to their length to maximise grip force performance. The present study aimed at providing quantitative evidence of the links between wrist posture, muscle capacities and grip capabilities. It combines experimental measurements and a musculoskeletal model including the force-length relationship of the four prime muscles used in grasping. Participants exerted their maximum grip force on a cylindrical dynamometer in four different wrist postures, including one freely chosen by participants (spontaneous). A musculoskeletal model computed the muscle force level and length from motion capture and muscle activation. Results revealed that participants exerted maximum grip force spontaneously, with a loss of force when using other postures. At muscle force and length level, grip force variation seems to be associated with all the muscles under study. This observation led to a first quantitative link between power grip, posture and muscle properties, which could provide more insight into neuromechanical interaction involved when grasping. The design of ergonomic devices could also benefit from this quantification of the relationship between wrist angle and muscle length properties.

Biomechanical Study of the Development of Long Bones: Finite Element Structure Synthesis of the Human Second Proximal Phalanx Under Growth Conditions

Torsional loads are a possible mechanical explanation for the architecture of long bone. Finite element structure synthesis (FESS) has previously successfully been used as a deductive technique using Wolff's Law by applying expected loads to an unspecific homogeneous solid and eliminating stress free parts to verify muscle forces. The extended approach presented in this article includes further mechanobiological rules to model the development from a cartilage model to a finger bone. In contrast to former computational models, simulation of processes leading to both external growth and internal differentiation are included. Combined axial and torsional loads synthesize a complete human secondary proximal phalanx model comparable to form and internal structure to that observed in vivo. While the computational model is very sensitive to initial alterations of loads, changes after growth have a minor effect as observed in animal models. Predictions of cartilage growth and ossification during FESS showed significant similarities to ontogeny indicating the importance of mechanical factors for the morphogenesis of bone during growth. Anat Rec, 302:1389-1398, 2019. © 2018 Wiley Periodicals, Inc.

Performing pull-ups with small climbing holds influences grip and biomechanical arm action

Pull-ups are often used by sport-climbers and other athletes to train their arm and back muscle capabilities. Sport-climbers use different types of holds to reinforce finger strength concomitantly. However, the effect of grip types on pull-up performance had not previously been investigated. A vertical force platform sensor measured the force exerted by climbers when performing pull-ups under six different grip conditions (gym-bar, large climbing hold, and four small climbing holds: 22mm, 18mm, 14mm, and 10mm). The electromyography of finger flexors and extensor muscles were recorded simultaneously. The maximal arm power and summed mechanical work were computed. The results revealed that the number of pull-ups, maximal power, and summed mechanical work decreased significantly with the size of the climbing hold used, even if no differences were found between a large climbing hold and a gym-bar. Electromyography of the forearm muscles revealed that the use of a climbing hold generated finger flexor fatigue and that the level of cocontraction was impacted by the different segment coordination strategies generated during the pull-ups. These findings are likely to be useful for quantifying training loads more accurately and designing training exercises and programs.

Real time relationship between individual finger force and grip exertion on distal phalanges in linear force following tasks

Individual finger force (FF) in a grip task is a vital concern in rehabilitation engineering and precise control of manipulators because disorders in any of the fingers will affect the stability or accuracy of the grip force (GF). To understand the functions of each finger in a dynamic grip exertion task, a GF following experiment with four individual fingers without thumb was designed. This study obtained four individual FFs from the distal phalanges with a cylindrical handle in dynamic GF following tasks. Ten healthy male subjects with similar hand sizes participated in the four-finger linear GF following tasks at different submaximal voluntary contraction (SMVC) levels. The total GF, individual FF, finger force contribution, and following error were subsequently calculated and analyzed. The statistics indicated the following: 1) the accuracy and stability of GF at low %MVC were significantly higher than those at high SMVC; 2) at low SMVC, the ability of the fingers to increase the GF was better than the ability to reduce it, but it was contrary at high SMVC; 3) when the target wave (TW) was changing, all four fingers strongly participated in the force exertion, but the participation of the little finger decreased significantly when TW remained stable; 4) the index finger and ring finger had a complementary relationship and played a vital role in the adjustment and control of GF. The middle finger and little finger had a minor influence on the force control and adjustment. In conclusion, each of the fingers had different functions in a GF following task. These findings can be used in the assessment of finger injury rehabilitation and for algorithms of precise control.

Grip force and force sharing in two different manipulation tasks with bottles

Grip force and force sharing during two activities of daily living were analysed experimentally in 10 right-handed subjects. Four different bottles, filled to two different levels, were manipulated for two tasks: transporting and pouring. Each test subject's hand was instrumented with eight thin wearable force sensors. The grip force and force sharing were significantly different for each bottle model. Increasing the filling level resulted in an increase in grip force, but the ratio of grip force to load force was higher for lighter loads. The task influenced the force sharing but not the mean grip force. The contributions of the thumb and ring finger were higher in the pouring task, whereas the contributions of the palm and the index finger were higher in the transport task. Mean force sharing among fingers was 30% for index, 29% for middle, 22% for ring and 19% for little finger. Practitioner Summary: We analysed grip force and force sharing in two manipulation tasks with bottles: transporting and pouring. The objective was to understand the effects of the bottle features, filling level and task on the contribution of different areas of the hand to the grip force. Force sharing was different for each task and the bottles features affected to both grip force and force sharing.