51,353 research outputs found
Changes in muscle morphology and neuromuscular function with eccentric strength training - Consequences for athletic performance
No full textChanges in muscle morphology and neuromuscular function with eccentric strength training - Consequences for athletic performance
No full textChanges in Muscle Morphology, Neuromuscular Capacity and Tendon Function with Training: Implications for Athletic Performance, Patient Rehabilitation and Aging Individuals
No full textResistance training is well known to induce adaptive changes in the morphology and architecture of human skeletal muscle, while also leading to adaptive changes in nervous system function (Aagaard, 2003, Aagaard et al., 2020). As discussed below, these changes contribute to the marked increase in maximal contractile muscle force and power that can be seen with resistance (strength) training not only in athletes but also in previously untrained persons, including frail and very old (>80 yrs) adults and patients. Perhaps most importantly, the training induced improvements in skeletal muscle size/architecture and neuromuscular function are translated into improved athletic performance in younger adults while correspondingly leading to an enhanced functional capacity during activities of daily living in aging individuals and patients, respectively.</p
Electromyographic evaluation of muscle strength exercise at low and high loading intensity
No full textElectromyographic evaluation of muscle strength exercise at low and high loading intensity
No full textThe role of pennation angle and architectural gearing to rate of force development in dynamic and isometric muscle contractions
Full text linkBackground: Associations between muscle architecture and rate of force development (RFD) have been largely studied during fixed-end (isometric) contractions. Fixed-end contractions may, however, limit muscle shape changes and thus alter the relationship between muscle architecture an RFD. Aim: We compared the correlation between muscle architecture and architectural gearing and knee extensor RFD when assessed during dynamic versus fixed-end contractions. Methods: Twenty-two recreationally active male runners performed dynamic knee extensions at constant acceleration (2000°s-2) and isometric contractions at a fixed knee joint angle (fixed-end contractions). Torque, RFD, vastus lateralis muscle thickness, and fascicle dynamics were compared during 0-75 and 75-150 ms after contraction onset. Results: Resting fascicle angle was moderately and positively correlated with RFD during fixed-end contractions (r = 0.42 and 0.46 from 0-75 and 75-150 ms, respectively; p < 0.05), while more strongly (p < 0.05) correlated with RFD during dynamic contractions (r = 0.69 and 0.73 at 0-75 and 75-150 ms, respectively; p < 0.05). Resting fascicle angle was (very) strongly correlated with architectural gearing (r = 0.51 and 0.73 at 0-75 ms and 0.50 and 0.70 at 75-150 ms; p < 0.05), with gearing in turn also being moderately to strongly correlated with RFD in both contraction conditions (r = 0.38-0.68). Conclusion: Resting fascicle angle was positively correlated with RFD, with a stronger relationship observed in dynamic than isometric contraction conditions. The stronger relationships observed during dynamic muscle actions likely result from different restrictions on the acute changes in muscle shape and architectural gearing imposed by isometric versus dynamic muscle contractions
Quick-clay landslide mitigation using potassium chloride
Full text linkHighly sensitive postglacial marine clays, termed quick clays, represent a risk for large retrogressive or progressive landslides such as the well-documented Rissa quick-clay landslide in 1978. Landslide susceptibility presents great challenges for construction work, even in the construction of landslide mitigation measures. Establishing large prevention berms is a commonly used method for increasing slope stability, but can often result in undesirable changes to the terrain. Ground improvement by potassium chloride (KCl) is herein considered as a possible alternative. However, detailed knowledge on geochemistry and its impact on the mechanical behaviour in clays is needed in developing efficient ground-improvement methods based on introducing salt into the clay-water system.
In 1972, salt wells filled with potassium chloride (KCl) were installed in a quick-clay deposit at Ulvensplitten, Oslo, Norway with the intention to improve the mechanical properties in the quick clay prior to excavation. Great emphasis was made in documenting the improved geotechnical properties with sampling and vane shear testing in the 2-3 years following the salt-well installations. The ground investigations revealed a significant increase in undrained and remoulded shear strength as well as in the Atterberg limits with increasing concentrations of potassium in the pore water. The collected pore-water chemistry data was, however, scarce and inconclusive with regard to determination of when the clay ceased to be quick; vital for estimating the time required to stabilize the quick-clay volume. The salt-well method is not used as ground improvement today, mainly due to the fact that it is time consuming and the effects are not fully understood or documented with regard to short and long-term effects.
In order to establish understanding and documentation, six salt wells filled with KCl were installed in January 2013 in a highly sensitive, low plastic quick-clay deposit at Dragvoll, Trondheim, Norway. The changed pore-water chemistry and improved properties around the wells were investigated by monitoring systems, sampling, laboratory and in-situ tests. The in-situ experiment at Dragvoll provides unique results on improvement of the geotechnical properties isolated to the impact of changed pore-water chemistry. The computer program PHREEQC was used for back calculations of the observed geochemical changes, suggesting that such simulations could be used for estimating the required time to stabilise the quick-clay volume surrounding the wells. Resistivity cone penetrations tests (RCPTU) were conducted in order to evaluate its effectiveness on detecting improved geotechnical properties in-situ. In addition, ground investigations were carried out 40 years after salt-well installations at Ulvensplitten to document the long-term effect of KCl-treated clays. The herein presented correlations between geotechnical properties and pore-water compositions in the salt-treated clay deposit at Dragvoll together with the data from Ulvensplitten, contributes to understand the mechanisms around KCl as ground improvement and its feasibility, as well as determining at which pore-water composition the clays render to be quick.
The collected historical and new data validate the KCl-well method as a landslide mitigation method inhibiting retrogressive landslide development, also reducing the risk for progressive Development
Jump capacity and mechanical muscle function in male and female elite volleyball players
No full textEffect of concentric- and eccentric-only strength training, and detraining, on the rate of force development of human skeletal muscle
No full textStrength training in elderly osteoarthritis (oa) patients: effects on maximum strength and rapid force characteristics
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