Biomedical subjects

Dick F Stegeman

Publications and source records attributed to Dick F Stegeman.

5 recordsLinked to original sources

PubMed2003

Relative contributions of central and peripheral factors to fatigue during a maximal sustained effort.

Local muscle fatigue can originate from both peripheral and central factors. The relative contribution of these factors in the course of a fatiguing contraction in 20 healthy subjects was determined. While subjects made a 2-min sustained maximal voluntary contraction (MVC) of the biceps brachii, muscle fibre conduction velocity (MFCV) was determined with surface electromyography (SEMG) as a representation of developing peripheral fatigue. To quantify the amount of peripheral fatigue, the force development following a train of electrical stimuli on the endplate before and after the contraction were compared. To measure force loss caused by central factors, superimposed electrical stimulation was used during the contraction. By two different methods the influence of peripheral fatigue on the superimposed force responses was taken into account. The first method compared the force response with the actual voluntary force, the second -which seemed more valid - used an estimation of peripheral fatigue based on linear interpolation between the force responses during rest before and after sustained contraction. During the contraction, voluntary force decreased to 38%. Peripheral fatigue was responsible for the larger part of this decline (89%). The other part, which was calculated as 12%, was caused by an increase of central activation failure. The decline of MFCV indicated that peripheral fatigue increased predominantly during the first half of the contraction and stayed at a constant level during the latter part. In contrast, central fatigue mainly induced a force decrease in the second part of the contraction. The different mechanisms which could be responsible for this change of emphasis from peripheral to central factors are discussed.

Adult↗

PubMed2003

Multichannel surface EMG: basic aspects and clinical utility.

The generation of the surface electromyogram (sEMG) is described with regard to the properties of the single muscle fiber action potential as source, the physical aspects of volume conduction and recording configuration, and the properties and firing pattern of motor units (MUs). The spatial aspect of the motor unit action potential (MUP) is emphasized in relation to the results of high-density, multichannel sEMG measurements. The endplate zone, depth, size, and position of MUs can be estimated. The use of muscle fiber conduction velocity measurements in channelopathies and the changes in pathological fatigue are described. Using the unique patterns of spatial spread of MUPs over the skin (MU fingerprint), MU classification and the determination of firing moments is done noninvasively. Clinical applications of high-density sEMG measurements are reviewed. Emerging possibilities provided by MUP size and fingerprint measurements in neuromuscular disease and motor control are discussed. We conclude that multichannel sEMG adds unique, and sometimes indispensable, spatial information to our knowledge of the motor unit.

Action Potentials↗

PubMed2003

Brain symmetry and topographic analysis of lateralized event-related potentials.

OBJECTIVE: We investigated the influence of symmetry assumptions implicit in the derivation and the use of event-related lateralized potentials (ERLs), such as the lateralized readiness potential (LRP). We describe these assumptions and demonstrate several alternative computational methods. METHODS: Using analytical methods and forward simulations, we computed the error in the ERL topography that results from deviations in symmetry between homologous brain areas. Based on analytical considerations we show that, for source analysis, the ERL derivation provides no benefits compared to a single subtraction of the two (left-lateralized and right-lateralized) conditions underlying the ERL. RESULTS: Relative errors of 10% in the ERL topography are found if the location of an active region in one hemisphere differs by 10 mm from the symmetric location as compared to the other hemisphere A difference of 30 degrees in orientation results in a relative error of the ERL of 40%. Differences in source strength between hemispheres result in an ERL error that is half the size of the relative strength difference. CONCLUSIONS: We estimate that, due to violations of the symmetry assumption underlying the ERL, errors in the ERL topography of 10-40% can be expected. Source analysis does not benefit from the ERL. In topographic mapping and source analysis, the double subtraction of the ERL should be approached with caution and the single subtraction of the ERPs of two lateralized conditions should be first analyzed whenever possible. We suggest that analyses based on the topography of the ERL should only be performed after the assumption of symmetry has been validated.

Brain↗

PubMed2002

What do we learn from motor unit action potentials in surface electromyography?

This article gives an overview of what multichannel surface electromyography can teach us about a motor unit. Background information is given about the generation of surface electromyography in general and surface motor unit potentials in particular. Furthermore, we describe how surface motor unit potentials are related to several motor unit characteristics, such as size, location, neuromuscular junction position, fiber length, fiber type, and metabolic fiber properties. In addition, we show how the spatial characteristics of multichannel surface electromyography can be used to obtain single-surface motor unit potentials. The possibilities, challenges, and problems are discussed. Finally, several examples of surface motor unit potential analyses are given.

Action Potentials↗

PubMed2002

Multi-channel EMG of the M. triceps brachii in rats during treadmill locomotion.

OBJECTIVES: The study aims at a precise characterisation of intramuscularly varying recruitment patterns within the triceps brachii muscle (long and lateral head; proximal, medial, distal regions) in the time course of averaged step cycles during locomotion. METHODS: The triceps brachii muscle of 15 Hannover rats was investigated with a supramuscular 16-electrodes grid during treadmill locomotion. Multi-channel electromyogram (EMG) was recorded simultaneously with high-speed videography. The rectified and smoothed EMG was time-normalised. EMG profiles and dynamic EMG-map series were calculated. Differences between EMG distribution patterns were tested by multivariate analysis of variance. RESULTS: In the pre-stance phase EMG activity increased especially in the proximal long head. It most likely propagated from lower muscle layers of the long head. During stance phase the EMG activity of the lateral head rose steeply and exceeded those of the long head in short time. The fastest steps show the highest EMG amplitudes. CONCLUSIONS: EMG registrations with grid electrodes help in the identification of intramuscular co-ordination processes during locomotion. While the EMG profiles characterise the time course, the topographical distribution is better represented in dynamic EMG interference maps. The dynamic changing activation patterns of triceps brachii depend on the phase of the step cycle. This clearly indicates the different functions of the muscle heads.

Animals↗