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Eccentric Contraction-Induced Muscle Fibre Adaptation
Hard-strength training induces strength increasing and muscle damage, especially after eccentric contractions. Eccentric contractions also lead to muscle adaptation. Symptoms of damage after repeated bout of the same or similar eccentrically biased exercises are markedly reduced. The mechanism of this repeated bout effect is unknown. Since electromyographic (EMG) power spectra scale to lower frequencies, the adaptation is related to neural adaptation of the central nervous system (CNS) presuming activation of slow-non-fatigable motor units or synchronization of motor unit firing. However, the repeated bout effect is also observed under repeated stimulation, i.e. without participation of the CNS. The aim of this study was to compare the possible effects of changes in intracellular action potential shape and in synchronization of motor units firing on EMG power spectra. To estimate possible degree of the effects of central and peripheral changes, interferent EMG was simulated under different intracellular action potential shapes and different degrees of synchronization of motor unit firing. It was shown that the effect of changes in intracellular action potential shape and muscle fibre propagation velocity (i.e. peripheral factors) on spectral characteristics of EMG signals could be stronger than the effect of synchronization of firing of different motor units (i.e. central factors)
Characterising the biofilm forming capabilities of Cystic Fibrosis Pseudomonas aeruginosa clinical isolates
Thermal Breakage and Self-Healing of a Polymer Chain under Tensile Stress
We consider the thermal breakage of a tethered polymer chain of discrete
segments coupled by Morse potentials under constant tensile stress. The chain
dynamics at the onset of fracture is studied analytically by Kramers-Langer
multidimensional theory and by extensive Molecular Dynamics simulations in 1D-
and 3D-space. Comparison with simulation data in one- and three dimensions
demonstrates that the Kramers-Langer theory provides good qualitative
description of the process of bond-scission as caused by a {\em collective}
unstable mode. We derive distributions of the probability for scission over the
successive bonds along the chain which reveal the influence of chain ends on
rupture in good agreement with theory. The breakage time distribution of an
individual bond is found to follow an exponential law as predicted by theory.
Special attention is focused on the recombination (self-healing) of broken
bonds. Theoretically derived expressions for the recombination time and
distance distributions comply with MD observations and indicate that the energy
barrier position crossing is not a good criterion for true rupture. It is shown
that the fraction of self-healing bonds increases with rising temperature and
friction.Comment: 25 pages, 13 picture
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