Effect of work experience and upper-limb muscle activity on grip strength of manual workers

Objectives. The current study correlated grip strength (GS) measurements with upper-limb muscle activity (UMA) for three different experience levels of manual workers (beginner, intermediate and advanced). Methods. A total of 182 male and female manual workers were chosen, and GS was assessed in some contexts using a digital handgrip dynamometer. Results. The GS values change significantly depending on the amount of experience of the workers. The difference in GS for different UMA demonstrates that continuous exposure to hand tools in different conditions of the hands (twisting, bending, etc.) significantly impacts manual arm strength. Conclusions. These findings suggest that repetitive use of hand tools in various manual operations (cutting, digging, pruning, spading, etc.) causes GS to vary significantly. In addition, beginner experience-level individuals exhibited much lower GS values in the dominant hand, whereas advanced experience-level workers had the greatest strength. Thus, for generating higher forces, professionals (advanced and intermediate levels) choose to execute safer activity (i.e., more neutral positions) than beginners.

Using essential oils from Citrus paradisi as a fumigant for Solenopsis invicta workers and evaluating the oils' effect on worker behavior

The red imported fire ant is one of the world's most devastating invasive species, adversely affecting humans, wildlife, crops, and livestock. To control infestations, chemical pesticides are deployed extensively around the world. However, their extensive use has led to negative effects on the environment and human health. Essential oils, which are safe and ecofriendly, can potentially be used as alternatives to chemical pesticides. In this study, grapefruit essential oils were used as fumigant agents to control red imported fire ants. The crude grapefruit oil (GO1) contained 28 compounds, and the concentrated grapefruit oil (GO2), which was refined from GO1 by vacuum distillation, contained 20 compounds. D-Limonene was the dominant constituent in both GO1 (70.1%) and GO2 (73.96%), and other important constituents included β-pinene, α-pinene, β-phellandrene, octanal, d-carvone, α-terpineol, and linalool. Both the essential oils and their individual constituents (α-pinene, α-terpineol, β-phellandrene, octanal, and d-carvone) showed strong lethal fumigant effects against workers. Workers were more susceptible to GO2 than GO1, and octanal was more toxic to workers as compared with the other four constituents. When antennas of workers were treated with the two oils or the five constituents, their walking and gripping abilities were significantly suppressed, and there was an obvious bending or breaking phenomenon on the sensilla of the antennas. Fumigant activity by grapefruit essential oils and their main compounds were associated with their effects on the walking and gripping behavior of workers, and this confirmed that grapefruit essential oil is a promising, ecofriendly, and safe fumigant for the control of red imported fire ants.

Neuromechanical control of the forearm muscles during gripping with sudden flexion and extension wrist perturbations

The purpose of this study was to investigate how gripping modulates forearm muscle co-contraction prior to and during sudden wrist perturbations. Ten males performed a sub-maximal gripping task (no grip, 5% and 10% of maximum) while a perturbation forced wrist flexion or extension. Wrist joint angles and activity from 11 muscles were used to determine forearm co-contraction and muscle contributions to wrist joint stiffness. Co-contraction increased in all pairs as grip force increased (from no grip to 10% grip), corresponding to a 36% increase in overall wrist joint stiffness. Inclusion of individual muscle contributions to wrist joint stiffness enhanced the understanding of forearm co-contraction. The extensor carpi radialis longus (ECRL) and brevis had the largest stiffness contributions (34.5 ± 1.3% and 20.5 ± 2.3%, respectively), yet muscle pairs including ECRL produced the lowest co-contraction. The muscles contributing most to wrist stiffness were consistent across conditions (ECRL for extensors; Flexor Digitorum Superficialis for flexors), suggesting enhanced contributions rather than muscular redistribution. This work provides investigation of the neuromuscular response to wrist perturbations and gripping demands by considering both co-contraction and muscle contributions to joint stiffness. Individual muscle stiffness contributions can be used to enhance the understanding of forearm muscle control during complex tasks.

Clinging, gripping, holding, containment: Reflections on a survival reflex and the development of a capacity to separate

This paper attempts to describe how, in the very first months of extra-uterine life, personality structures are formed around notions of personal space, separateness, attachment and individuation. The contribution of a forgotten Hungarian analyst, Imre Hermann, who wrote about the 'clinging reflex', will be explored in relation to the origin of Bowlby's concept of attachment and Rey's theoretical understanding of personal space. Particular attention will be given to transitions, transitional experiences and the development of a sense of internal space. Vignettes from infant observations will be used to illustrate the theoretical frame of reference. Clinical material from the analysis of a child and an adult patient will be provided to postulate how a distorted perception of personal space and separateness in the first few months of life may affect the capacity to attach and to individuate.