Muscle force compensation among synergistic muscles after fatigue of a single muscle

PurposeThe aim of this study was to examine control strategies among synergistic muscles after fatigue of a single muscle. It was hypothesized that the compensating mechanism is specific for each fatigued muscle.MethodsThe soleus (SOL), gastrocnemius lateralis (GL) and medialis (GM) were fatigued in separate sessions on different days. In each experiment, subjects (n = 11) performed maximal voluntary contractions prior to and after fatiguing a single muscle (SOL, GL or GM) while the voluntary muscle activity and torque were measured. Additionally, the maximal single twitch torque of the plantarflexors and the maximal spinal reflex activity (H-reflex) of the SOL, GL and GM were determined. Fatigue was evoked using neuromuscular stimulation.ResultsFollowing fatigue the single twitch torque decreased by −20.1%, −19.5%, and −23.0% when the SOL, GL, or GM, have been fatigued. The maximal voluntary torque did not decrease in any session but the synergistic voluntary muscle activity increased significantly. Moreover, we found no alterations in spinal reflex activity.ConclusionsIt is concluded that synergistic muscles compensate each other. Furthermore, it seems that self-compensating mechanism of the fatigued muscles occurred additionally. The force compensation does not depend on the function of the fatigued muscle.     

Toward a Commonsense Answer to the Special Composition Question

The special composition question is the question, ‘When do some things compose something?’ The answers to this question in the literature have largely been at odds with common sense, either by allowing that any two things (no matter how apparently unrelated) compose something, or by denying the existence of most ordinary composite objects. I propose a new ‘series-style’ answer to the special composition question that accords much more closely with common sense, and I defend this answer from van Inwagen's objections. Specifically, I will argue (among other things) that the proposed answer entails the transitivity of parthood, that it is non-circular, and that it casts some light on the ancient puzzle about the Ship of Theseus.     

Editorial Notice

Abstract

John McDowell has claimed that the rational link between perceptions and empirical judgements allows us to perceive objects as belonging to a wider reality, one which extends beyond the objects perceived. In this way, we can be said to have a perceptual awareness of the world. I argue that McDowell's account of this perceptual awareness does not succeed. His account as it stands does not have the resources to explain how our perceptions can present objects as belonging to a wider reality, regardless of the judgements we make about that reality. I suggest that we can give a better account of this perceptual awareness of the world by appealing to transcendental phenomenology. A phenomenological study of perceptual experiences describes how they are structured by a sense of the perceived objects as belonging to a world containing other objects of possible perception. I shall outline this sense we have of the world, and argue that it allows us to perceive objects as belonging to a wider reality. Transcendental phenomenology can thus help to explain our perceptual awareness of the world.     

组织类型与员工建言行为的关系探索：基于权力的视角

研究目的是探索中国背景下国有企业、民营企业、外资企业、政府机关四类组织中员工建言行为的差异,及员工个人权力感和权力动机的中介作用。采用问卷法对员工和管理者进行配对取样调查,通过对回收的324份有效问卷进行数据分析。结果表明,员工建言行为在四种组织类型中存在显著性差异,而员工个人权力感和权力动机在其中起到中介作用。此外,研究还发现,权力距离倾向在组织类型和个人权力感之间起到调节作用。最后,研究梳理了组织类型与建言行为的关系模型,并对未来研究做了展望。     

Water as a Commons: An Exploratory Study on the Motives for Collective Action Among Italian Water Movement Activists

In many communities, supplying water and sanitation is a huge task, and the fact that these essential services can be carried out by the private sector is a debated issue. This article presents an exploratory study aimed to identify the range of motives for collective action shared by activists of the Italian Movement for ‘Public Water’. In‐depth interviews were conducted with 28 activists and were qualitatively analysed. Five main motivational categories emerged: defending the right to water, preserving community ties, opposing to the Government and ‘water sellers’, preserving the environment and money interests. Each motive is based on a specific representation of the issue of water and privatization process. Findings provide further support for the importance of moral convictions and sense of community in collective action development and suggest a critical reconsideration of the role played by collective efficacy. The results are discussed in the framework of the psychosocial literature on collective action and community psychology perspectives on participatory processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Patterns of Aggression in Parents and their Children

In this research, we examined children's awareness of inconsistencies in messages that are meaningful for children, instructions for games. In the first experiment, kindergarten (n = 25) and second- (n = 25) and fourth-grade (n = 26) children were individually read the instructions for two games, each of which included two inconsistent statements. Chi-square analyses yielded a significant effect for grade for one game (p < .05) and a marginally significant effect for a second game (p < .10). In a second experiment, second- (n = 40), fourth- (n = 40), and sixth-grade (n = 40) children were read the instructions for two games, each of which included two statements that were inconsistent. An analysis of variance demonstrated that with an increase in grade, there was a significant increase (p < .001) in awareness that a message contained an inconsistency. The analysis also indicated that the subjects were more willing (p < .08) to question an adult than they were to question a child about an inconsistency. Moreover, a regression analysis indicated that awareness of inconsistencies in the rules for games was significantly related to memory (p < .001) and to one's ability to note inconsistencies in shorter, simpler messages (p < .001).     

Force Control Is Greater in the Upper Compared With the Lower Extremity

The authors investigated whether force control is similar between the upper and lower limbs and between contractions that involve 1 or 2 joints. Six volunteers (27.5 ± 11.2 years of age) attempted to produce consistent discrete rapid force responses of 30, 60, and 90 N by using 6 different body postures, 3 with the upper and 3 with the lower limb. One of the postures for each limb involved 2 joints. The standard deviation of peak force and impulse (aggregate of the force-time curve) was significantly greater (?25%) for the lower limb than for the upper limb (p < .01). Contractions that involved 1 or 2 joints within a limb had similar variability. Therefore, the upper limb might have better control of force than the lower limb because of its extensive use in fine motor tasks in daily activities.     

Coordination of Grip Configurations as a Function of Force Output

In this investigation, the authors examined the coordination and control of force production by the digits of the hand as a function of criterion force level and grip configuration. Each adult participant (N = 6: 3 men and 3 women) was required to place the thumb and a finger (or fingers) upon load cells that were fixed to a grasping apparatus that was clamped to a table. In the task, participants had to match a criterion continuous constant total force level displayed on a computer screen. There were 10 trials at each grip configuration and criterion force level combination on each of 3 consecutive days. The results showed that (a) different grip configurations minimized error at each force level; (b) there was a specific digit pairing within a given grip configuration that produced the highest correlation of force output; (c) the correlation between the force output of digits generally increased at higher force levels; (d) error was reduced at each force level and grip configuration over the practice period; and (e) the organization of the force output of each digit varied as a function of digit, force level, grip configuration, and practice. The findings are consistent with the hypothesis that coordination of the digits in prehension is reflective of an adaptive, task-specific solution that is modified with practice.     

After-Contraction Phenomenon: Influences on Performance and Learning

Three experiments investigated the influence of an after-contraction phenomenon on the performance and learning of a dynamic force-production task. The after-contraction effect refers to an involuntary potentiation (induced by a sustained pre-contraction) that is thought to summate with voluntary motor commands to bias subsequent responding. The precontraction involved a brief (20 s) static contraction. The subsequent influence of the precontraction on a dynamic force-production task was assessed. Experiments 1 and 2 were aimed at demonstrating the direct impact of the precontraction intensity on the magnitude and decay of the after-contraction effect. The results indicated that as the intensity of the precontraction increased, the magnitude of the induced bias increased. In Experiment 3, the indirect influence on subsequent retention of varying the precontraction intensity during acquisition was investigated. The results indicated that the performance of subjects experiencing varying precontraction intensities during acquisition was inferior to that of subjects experiencing a constant precontraction intensity, but the performance of the varied precontraction intensities group was superior on the test of retention. It is noted that the paradoxical reversal from acquisition to retention is similar to that found in contextual interference experiments and may arise from similar mechanisms.     

Shoulder Joint Position Sense Improves With External Load

Joint position sense (JPS) is important in the maintenance of optimal movement coordination of limb segments in functional activities. Researchers have shown that the sensitivity of musculotendinous mechanoreceptors increases as muscle activation levels increase. In the present study, when 25 participants tried to replicate the same presented position, both vector and elevation angle repositioning errors decreased linearly as the external load increased up to 40% above unloaded shoulder torque. However, external load had no effect on plane repositioning error. The results indicated that JPS increased under conditions of increasing external load but only in the direction of the applied load. That finding indicates that JPS acuity improves as muscle activation levels increase.