1,721,124 research outputs found
Muscle strength, power and adaptations to resistance training in older people
No full textMuscle strength and, to a greater extent, power inexorably decline with ageing. Quantitative loss of muscle mass, referred to as sarcopenia, is the most important factor underlying this phenomenon. However, qualitative changes of muscle fibres and tendons, such as selective atrophy of fast-twitch fibres and reduced tendon stiffness, and neural changes, such as lower activation of the agonist muscles and higher coactivation of the antagonist muscles, also account for the age-related decline in muscle function. The selective atrophy of fast-twitch fibres has been ascribed to the progressive loss of motoneurons in the spinal cord with initial denervation of fast-twitch fibres, which is often accompanied by reinnervation of these fibres by axonal sprouting from adjacent slow-twitch motor units (MUs). In addition, single fibres of older muscles containing myosin heavy chains of both type I and II show lower tension and shortening velocity with respect to the fibres of young muscles. Changes in central activation capacity are still controversial. At the peripheral level, the rate of decline in parameters of the surface-electromyogram power spectrum and in the action-potential conduction velocity has been shown to be lower in older muscle. Therefore, the older muscle seems to be more resistant to isometric fatigue (fatigue-paradox), which can be ascribed to the selective atrophy of fast-twitch fibres, slowing in the contractile properties and lower MU firing rates. Finally, specific training programmes can dramatically improve the muscle strength, power and functional abilities of older individuals, which will be examined in the second part of this review
Comparison between young and older women in explosive power output and its determinants during a single leg-press action after optimisation of load
No full textLower limb explosive power, which is more predictive of functional difficulties than strength per se with women being more at risk than men for disability, has been previously compared between young and older women using systems with fixed inertia. Individuals may have been obliged to use a percentage of their maximum strength that is not ideal for performing the movement at the optimum speed for maximum power output. This study was designed to compare explosive power output and its two determinants, optimal force and optimal speed, during a leg-press action between young and older women after optimising the load for maximum power production. The experiments were carried out on 20 women in good physical condition: 10 older, aged between 65 and 74 years and 10 young, aged between 18 and 30. Explosive power output was measured by setting the initial load at different percentages of maximum isometric strength and measuring the corresponding speed of movement during a leg-press action of the dominant leg. Maximum peak power, which was obtained at 60% of maximum isometric strength in both young and older women, was 61% lower in the older women (P<0.0001). This was due to a 52% lower optimal force (P<0.0001) and 21% lower optimal speed (P<0.01). The ratio of peak power to maximum isometric strength was 22.1% lower in the older women (P<0.01). After optimising the load, both lower speed of movement and lower strength determine the lower levels of power in older women. Power is more affected by ageing than isometric strength
The effect of active warm-up on surface emg power spectrum and muscle performance in healthy humans
No full textThe effect of an active warm-up on maximal voluntary contraction (MVC), maximal instantaneous power output and surface EMG (sEMG) parameters was studied. Eight volunteers [mean (SD) 22 (4) years] completed two trials on the same day, one control (CO), and the other preceded by an active cycling warm-up (WU) at 70% ventilatory threshold determined by the ventilatory equivalent method. Quadriceps muscle temperature, measured from vastus lateralis with a flexible thermistor, was 33.8 (0.4)°C in CO compared to 36.8 (0.5)°C in WU (P<0.05). Aural temperature, measured by an infrared tympanic thermistor, was not different between conditions. Experimental trials consisted of three knee-extension maximum voluntary contractions at a 90° angle with simultaneous recording of sEMG from the vastus lateralis, followed by three squat jumps performed on a force platform. SEMGs were analysed in the frequency domain as median frequency (MDF) and in the time domain as root mean square (RMS). MDF was 59.2 (14.1) Hz in CO compared to 67.2 (11.8) Hz in WU (P<0.05), while RMS was higher in CO compared to WU [0.65 (0.28) mV vs. 0.56 (0.19) mV; P<0.05]. MVC was not different [465.7 (107.6) N vs. 490.1 (117.2) N], whilst instantaneous power output during the squat jump was significantly higher in the WU trial [3324 (866) W vs. 3569 (919) W; P<0.05]. These data show MDF to be altered with an active warm-up, which would relate to a greater conduction velocity. This may translate into faster activation of the muscle fibres, thus partly explaining the increase in power output
The use of leaves of Olea europaea L. as passive samplers for polycyclic aromatic hydrocarbons. Assessment of the quality of the air in Palermo
No full textInterest in polynuclear aromatic hydrocarbons (PAHS), both from an analytical and an environmental point of view, arises from the fact that although most of them have absolutely no practical use, they are widely diffused into the environment. Their widespread distribution means that every individue is unwittingly exposed to the action of this class of substances, in working environments, in the home and in the open air. In this paper, Oleae europaea leaves have been used as passive samplers. The correlation obtained clearly shows that the quantitative analysis of PAHs in the Olea leaves permits to evaluate the quality of air, in a determined geographic area, without the need of making long samplers with complicate strumentation. The results of the analysis on the leaves give mediate information on the period from put forth buds to the collection without influence of meteorological conditions at the time of sampler
A recurrence-free variant of strassen’s algorithm on hypercube
No full textIn this paper a non-recursive Strassen’s matrix multiplication algorithm is presented. This new algorithm is suitable to run on parallel environments. Two computational schemes have been worked out exploiting different parallel approaches on hypercube architecture. A comparative analysis is reported. The experiments have been carried out on an nCUBE-2 supercomputer, housed at CNUCE in Pisa, supporting the Express parallel operating system. © 1995, Taylor & Francis Group, LLC. All rights reserved
QAL-BP: an augmented Lagrangian quantum approach for bin packing
No full textThe bin packing is a well-known NP-Hard problem in the domain of artificial intelligence, posing significant challenges in finding efficient solutions. Conversely, recent advancements in quantum technologies have shown promising potential for achieving substantial computational speedup, particularly in certain problem classes, such as combinatorial optimization. In this study, we introduce QAL-BP, a novel Quadratic Unconstrained Binary Optimization (QUBO) formulation designed specifically for bin packing and suitable for quantum computation. QAL-BP utilizes the Augmented Lagrangian method to incorporate the bin packing constraints into the objective function while also facilitating an analytical estimation of heuristic, but empirically robust, penalty multipliers. This approach leads to a more versatile and generalizable model that eliminates the need for empirically calculating instance-dependent Lagrangian coefficients, a requirement commonly encountered in alternative QUBO formulations for similar problems. To assess the effectiveness of our proposed approach, we conduct experiments on a set of bin packing instances using a real Quantum Annealing device. Additionally, we compare the results with those obtained from two different classical solvers, namely simulated annealing and Gurobi. The experimental findings not only confirm the correctness of the proposed formulation, but also demonstrate the potential of quantum computation in effectively solving the bin packing problem, particularly as more reliable quantum technology becomes available
Optimizing Deep Learning Models for Cell Recognition in Fluorescence Microscopy: The Impact of Loss Functions on Performance and Generalization
No full textIn the rapidly evolving domain of fluorescence microscopy, the application of Deep Learning techniques for automatic cell segmentation presents exciting opportunities and challenges. In this work, we investigate the impact of loss functions and evaluation metrics on model performance and generalization in the context of cell recognition.
First, we present extensive experiments with different commonly used loss functions and offer practical insights and guidelines, underscoring how the choice of a loss function can influence model performance.
Second, we conduct a detailed examination of several evaluation metrics with their relative benefits and drawbacks, helping to guide effective model evaluation and comparison in the field.
Third, we discuss how characteristics specific to fluorescence microscopy data impact model generalization. Precisely, we examine how factors such as cell sizes, color irregularities, and textures can potentially affect the performance and adaptability of these models to new data.
Collectively, these insights provide an understanding of the various facets resulting from the application of Deep Learning for automatic cell segmentation, shedding light on best practices, evaluation strategies, and model generalization. Hence, this study can serve as a beneficial resource for researchers and practitioners working on similar applications, fostering further advancements in the field
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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