Increased gravitational force reveals the mechanical, resonant nature of physiological tremor

Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head-to-foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system.This work was funded by a BBSRC Industry Interchange Award to J.P.R.S. and R.F.R. C.J.O. was funded by BBSRC grant BB/I00579X/1. C.A.V. was funded by A∗Midex (Aix-Marseille Initiative of Excellence

The Influence of Forearm and Wrist Orientation on Static Grip Strength as a Design Criterion for Hand Tools

The amount of force required to use a hand tool and its relationship to the user's capacity to exert this force is a critical design criterion of hand tools, often affecting the immediate safety of the tool user and the propensity of the tool to cause injury to the user with long-term use. Because the wrist is often placed in deviated positions, the available data on grip strength with an undeviated wrist configuration may not be applicable to the design of many hand tools. This study demonstrates the decreases in grip strength due to wrist deviations and forearm rotation. The position of maximal static grip strength is the neutral wrist with a supinated forearm. Decrements from the neutral position for wrist flexion, hyperextension, radial flexion and ulnar flexion are 30%, 22%, 18% and 15%, respectively. The pronated forearm allows only 87% of the strength of the supinated forearm, and the differences between the supinated and the midposition forearm are not significant.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

The effect of pose variability and repeated reliability of segmental centres of mass acquisition when using 3D photonic scanning

Three-dimensional (3D) photonic scanning is an emerging technique to acquire accurate body segment parameter data. This study established the repeated reliability of segmental centres of mass when using 3D photonic scanning (3DPS). Seventeen male participants were scanned twice by a 3D whole-body laser scanner. The same operators conducted the reconstruction and segmentation processes to obtain segmental meshes for calculating the segmental centres of mass. The segmental centres of mass obtained from repeated 3DPS were compared by relative technical error of measurement (TEM). Hypothesis tests were conducted to determine the size of change required for each segment to be determined a true variation. The relative TEMs for all segments were less than 5%. The relative changes in centres of mass at ±1.5% for most segments can be detected (p < 0.05). The arm segments which are difficult to keep in the same scanning pose generated more error than other segments

Further improvement in a criterion for human stability in floodwaters

There have been numerous urban flood disasters in recent years, causing a considerable loss of human life. An improved criterion in the form of incipient velocity has been proposed for human stability in floodwaters, and it is specifically for deep waters where toppling instability generally occurs, and it can account for the posture of leaning forward of a human body in floodwater and the process of pivoting around heels at instability. Moreover, the previous equation of buoyancy force was modified using the parameters of human body structure for a typical American or European in ergonomics. Two parameters in the formula of incipient velocity were calibrated using existing experimental data based on real human subjects, with the improved stability criterion curves being presented for children and adults in floodwaters. Finally, the proposed formula was validated in detail against existing laboratory measurements, and the simple method was given to evaluate the flood hazard degrees for children and adults, based on the calculated incipient velocities at toppling instability and the corresponding incoming flow velocities

A biologically inspired neural network controller for ballistic arm movements

<p>Abstract</p> <p>Background</p> <p>In humans, the implementation of multijoint tasks of the arm implies a highly complex integration of sensory information, sensorimotor transformations and motor planning. Computational models can be profitably used to better understand the mechanisms sub-serving motor control, thus providing useful perspectives and investigating different control hypotheses. To this purpose, the use of Artificial Neural Networks has been proposed to represent and interpret the movement of upper limb. In this paper, a neural network approach to the modelling of the motor control of a human arm during planar ballistic movements is presented.</p> <p>Methods</p> <p>The developed system is composed of three main computational blocks: 1) a parallel distributed learning scheme that aims at simulating the internal inverse model in the trajectory formation process; 2) a pulse generator, which is responsible for the creation of muscular synergies; and 3) a limb model based on two joints (two degrees of freedom) and six muscle-like actuators, that can accommodate for the biomechanical parameters of the arm. The learning paradigm of the neural controller is based on a pure exploration of the working space with no feedback signal. Kinematics provided by the system have been compared with those obtained in literature from experimental data of humans.</p> <p>Results</p> <p>The model reproduces kinematics of arm movements, with bell-shaped wrist velocity profiles and approximately straight trajectories, and gives rise to the generation of synergies for the execution of movements. The model allows achieving amplitude and direction errors of respectively 0.52 cm and 0.2 radians.</p> <p>Curvature values are similar to those encountered in experimental measures with humans.</p> <p>The neural controller also manages environmental modifications such as the insertion of different force fields acting on the end-effector.</p> <p>Conclusion</p> <p>The proposed system has been shown to properly simulate the development of internal models and to control the generation and execution of ballistic planar arm movements. Since the neural controller learns to manage movements on the basis of kinematic information and arm characteristics, it could in perspective command a neuroprosthesis instead of a biomechanical model of a human upper limb, and it could thus give rise to novel rehabilitation techniques.</p

A computerized biomechanical model--Development of and use in studying gross body actions

Gross body actions involved in heavy industry, e.g. lifting and carrying materials, are often the cause of injury to the musculoskeletal system. A computer model is developed which treats the human body as a series of seven links from which reactive forces and torques are computed at each articulation during various simulated materials handling tasks. In addition, an analysis of shearing and compressing forces at the lower lumbar spine is included. The assumptions of the present model are presented, along with a discussion of future models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32890/1/0000269.pd

Movement consistency during repetitive tool use action

The consistency and repeatability of movement patterns has been of long-standing interest in locomotor biomechanics, but less well explored in other domains. Tool use is one of such a domain; while the complex dynamics of the human-tool-environment system have been approached from various angles, to date it remains unknown how the rhythmicity of repetitive tool-using action emerges. To examine whether the spontaneously adopted movement frequency is a variable susceptible to individual execution approaches or emerges as constant behaviour, we recorded sawing motion across a range of 14 experimental conditions using various manipulations. This was compared to free and pantomimed arm movements. We found that a mean (SD) sawing frequency of 2.0 (0.4) Hz was employed across experimental conditions. Most experimental conditions did not significantly affect the sawing frequency, signifying the robustness of this spontaneously emerging movement. Free horizontal arm translation and miming of sawing was performed at half the movement frequency with more than double the excursion distance, showing that not all arm movements spontaneously emerge at the observed sawing parameters. Observed movement frequencies across all conditions could be closely predicted from movement time reference data for generic arm movements found in the Methods Time Measurement literature, highlighting a generic biomechanical relationship between the time taken for a given distance travelled underlying the observed behaviour. We conclude that our findings lend support to the hypothesis that repetitive movements during tool use are executed according to generic and predictable musculoskeletal mechanics and constraints, albeit in the context of the general task (sawing) and environmental constraints such as friction, rather than being subject to task-specific control or individual cognitive schemata

Indonesian anthropometry update for special populations incorporating Drillis and Contini revisited

Nowadays, research on anthropometry becomes more essential, and yet, it is critical due to its implication and contribution to product and system design. Since it deals with human capability and limitation on physical activities, its role becomes more important, especially, when it comes to the needs for special populations. This study provides a comparative study between elderly and children anthropometry using Drillis and Contini approach incorporating Chinese and non-Chinese ethnic groups. More than 1000 subjects involved in this study. After the data refinement process, there were 498 valid data for children (i.e., 98 Chinese male, 136 non-Chinese male, 134 Chinese female, and 130 non-Chinese female), and 556 valid data for elderly (i.e., 186 Chinese male, 148 non-Chinese male, 115 Chinese female, and 107 non-Chinese female). In general, the finding shows that elderly (both male and female, both Chinese and non-Chinese) tends to have similar size and pattern with adult. Whilst, male and female children of 6e9 years sub-group (both Chinese and non-Chinese sub-group) tend to have higher weight ratio, compared to elderly and the children of 10e12 years sub-group. It was easily recognized that the children tend to have higher rate for limb segments compared to other body dimensions. At all sample groups, the eye height and shoulder height were found to be highly correlated with stature. Moreover, related to body weight, all samples show that thigh thickness and abdominal depth were deemed to be significant measures to be associated with. The expected contribution of this study is that to update the Indonesian special population anthropometry and to identify which measures are significantly associated with stature and weight, respectively with regard to different special population and given limited anthropometric data. Practically, given the data of stature and body weight, product designer can predict the anthropometric characteristics for special population