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At least 1,153 records · Page 64Linked to original sources
PubMed2005

Why does knee extensor muscles torque decrease after eccentric-type exercise?

AIM: The purpose of this study was to re-examine central and peripheral origins of neuromuscular fatigue after a highly strenuous eccentric exercise of the knee extensor muscles (KE) using both voluntary/evoked contractions and electromyographic recordings (EMG). METHODS: Before, and 30 min after 15 min of intermittent one-logged downhill running, maximal percutaneous electrical stimulations (single twitch, 0.5 s tetanus at 20 Hz and 80 Hz) were applied to the femoral nerve of 10 male subjects. Electrically evoked superimposed twitches were delivered during isometric maximal voluntary contraction (MVC) to determine maximal voluntary activation (%VA). Vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF) EMG were recorded during MVC and quantified using the root mean square (RMS) value. M-wave characteristics were also determined. RESULTS: KE MVC and %VA decreased significantly with fatigue (-19.6+/-6.1%; P<0.001 and -7.8+/-6.6%; P<0.01, respectively). Peak tetanus tension at 20 and 80 Hz (P20 and P80, respectively) declined (P<0.001), concurrently with a decrement of the P20 x P80(-1) ratio (-37.3+/-16.6%; P<0.001). Antagonist muscle coactivation, RMS to M-wave peak-to-peak amplitude and MVC x P80(-1) ratios were unchanged after the fatiguing exercise. CONCLUSIONS: The results reveal that part of the large loss in MVC may have a central origin but most of the MVC decrement is due to the presence of low-frequency fatigue while possible contractile failure cannot be excluded.

Adult↗
PubMed1995

The force requirements for tooth movement. Part II: Uprighting and root torque.

In orthodontic treatment tooth root movement is essential, not only to obtain mesio-distal paralleling of individual tooth roots, but also to achieve correct axial inclinations in relation to basal bones and inter-incisal angles in the anterior segments. This article describes a pilot study in which paired teeth on opposite sides of the mouth and which required root paralleling as a part of orthodontic treatment, were subjected to known moments of force. The forces were exerted using helical torsion springs of predetermined load-deflection characteristics. Average weekly moments of force were related to the weekly rates of angular movement of eight teeth in a group of four patients. The experiments lasted for up to seven weeks and were designed so that the movement of the paired teeth in each patient were concurrent.

Cuspid↗
PubMed1980

Torque and cognitive ability: some contradictions to Blau's proposals.

Investigated with two spatial and language tasks Blau's (1977a) theory that clockwise directionality in circle drawing indicates neural integration difficulties. The tasks were administered to 106 children of approximately 8 years of age, and the data were analyzed for sex differences and circling behavior. None of the hypotheses based on Blau's theory was supported, and some significant results in the opposite direction to predictions were found. Aspects of the results that may be of potential future research interest are identified.

Child↗
PubMed1996

Reproducibility of isometric trunk extension torque, trunk extensor endurance, and related electromyographic parameters in the context of their clinical applicability.

Testing the capacity of the trunk extensor muscles may be useful in the diagnosis of low back pain. In the present study, the reproducibility of measurements of maximum trunk extension force, trunk extension endurance, and related electromyographic parameters was investigated. Intraclass correlations indicated that the reproducibility of maximum force and endurance time was satisfactory. Nevertheless, the smallest difference in these parameters that could be attributed, with 95% confidence, to a change in the condition of a patient was, in general, more than 20%. On the electromyograms, the slopes of amplitude and frequency content appeared to be related to endurance time. The reproducibility of these parameters in terms of the intraclass correlation was again satisfactory; however, the smallest detectable difference generally exceeded 50%. The clinical applicability of the parameters studied is severely limited by a lack of reproducibility.

Adult↗
PubMed2000

Drag and Torque on Clusters of N Arbitrary Spheres at Low Reynolds Number.

Hydrodynamics of particle clusters suspended in viscous fluids is a subject of considerable theoretical and practical importance. Using a multipole expansion of the flow velocity in a series of spherical harmonics, Lamb's fundamental solution of the Stokes flow outside a single sphere is generalized in this work to the case of N nonoverlapping spheres of arbitrary size with slip boundary conditions. The expansion coefficients are found by transforming the boundary conditions to the Lamb form and by transforming the spherical coordinates and solid spherical harmonics centered at different spheres. The problem is reduced to the solution of the linear system of equations for the expansion coefficients, which is carried out numerically. Based on the developed theory, the relation between the hydrodynamic and gyration radius of fractal-like aggregates with different structure is established. In another application, an asymptotic slip-regime dependence of the aggregate hydrodynamic radius on the Knudsen number and the number of particles is found by performing calculations of drag forces acting on the gas-borne fractal-like and straight chain aggregates. A good agreement is shown in comparing predictions of the described theory with available experimental and theoretical results on motion of various small sphere clusters in viscous fluid. Copyright 2000 Academic Press.

Journal Article↗
PubMed1995

Relations between joint torque, motion, and electromyographic patterns at the human elbow.

Voluntary movements may be considered kinematic actions resulting from the neural control patterns that activate the motoneuron pools. One school of thought proposes that specific features of the intended kinematic trajectory such as the duration of acceleration are used by the central nervous system to plan muscle activation patterns. Our own experience suggests that it is the intended force trajectory that is directed by muscle activation patterns. Although under many circumstances these two approaches lead to indistinguishable behavior patterns, examples of movements that are incompatible with the former but not the latter approach are presented in this manuscript.

Biomechanical Phenomena↗