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Voluntary activation of skeletal muscle in young and old women and men

Miller, Michael LU (2004)
Abstract (Swedish)
Popular Abstract in Swedish

En viktig del av sjukgymnastens kliniska undersökning är att bedöma muskelstyrka. För att kunna planera och genomföra en adekvat behandling krävs en objektive mätning av muskelstyrkan och en förståelse av de faktorer som orsakar muskelsvaghet. En faktor som kan bidra till muskelsvaghet är en oförmåga hos centrala nervsystemet att rekrytera och optimalt aktivera de motoriska framhornscellerna i ryggmärgen. En reducerad viljemässig aktivering benämns nedsatt central aktiveringsoförmåga. En metod att bedöma viljemässig aktivering samt att upptäcka och kvantifiera nedsatt central aktiveringsoförmåga är att elektriskt stimulera muskeln en maximal viljemässig statiskt kontraktion. Om stimuleringen... (More)
Popular Abstract in Swedish

En viktig del av sjukgymnastens kliniska undersökning är att bedöma muskelstyrka. För att kunna planera och genomföra en adekvat behandling krävs en objektive mätning av muskelstyrkan och en förståelse av de faktorer som orsakar muskelsvaghet. En faktor som kan bidra till muskelsvaghet är en oförmåga hos centrala nervsystemet att rekrytera och optimalt aktivera de motoriska framhornscellerna i ryggmärgen. En reducerad viljemässig aktivering benämns nedsatt central aktiveringsoförmåga. En metod att bedöma viljemässig aktivering samt att upptäcka och kvantifiera nedsatt central aktiveringsoförmåga är att elektriskt stimulera muskeln en maximal viljemässig statiskt kontraktion. Om stimuleringen orsakar en ökning av muskelstyrkan anses det finna en nedsatt central aktiveringsförmåga.



Syftet med denna avhandling var att: i) vidareutveckla den elektriska stimuleringsmetoden för att mäta viljemässig aktivering och upptäcka och kvantifiera nedsatt aktiveringsförmåga; ii) använda den elektriska stimuleringsmetoden för att kartlägga viljemässig aktivering i lårmuskulaturen hos friska, aktiva, unga och gamla kvinnor och män; och iii) utvärdera graden av obehag från den elektriska stimuleringen. Vid mätning av den viljemässig aktiveringen.



Två metodologiska studier genomfördes där en modell av nedsatt aktiveringsförmåga utvecklades. Försökspersonernas lårmuskulatur stimulerades vid 80% av maximal muskelstyrka. Effekterna av olika stimuleringar på storleken av muskelstyrkaökningen och variabiliteten, samt effekterna på försökspersonernas upplevda obehag utvärderades. Obehaget mättes med en 100 mm visuell analogskala (VAS-pain). Ett elektriskt pulståg med en frekvens av 100 Hz gav en betydligt större ökning av muskelstyrkan jämfört med en enkel elektrisk impuls och är att föredra som stimuleringssätt när man studerar viljemässig aktivering av muskulaturen. Det fanns ingen skillnad i storleken på ökningen av muskelstyrkan när pulståg på 100 ms, 200 ms eller 300 ms användes och inte heller mellan pulståg med 150 V eller 200 V. Pulståg på 100 ms gav mindre variabilitet än pulståg med längd 50ms men obehaget var större med pulståg på 100 ms jämfört med 50 ms. Pulståg med pulsbredd på 0.1 ms och 0.2 ms gav lika stora ökningar av muskelstyrkan men pulståg med en pulsbredd av 0.1 ms gav mindre obehag. De unga individerna hade förmågan att fullt ut viljemässigt aktivera sin lårmuskulatur men inte vid varje försök. De äldre männen uppnådde lika höga aktiveringsnivåer som de unga individerna, men äldre kvinnor visade lägre aktiveringsnivåer och några äldre kvinnor uppnådde inte full aktivering i något försök. Medelvärdena för skattningarna av obehag från den elektriska stimuleringen var 35 mm för de unga individerna och 40 mm för de äldre. Dessa resultat visar att obehaget generellt var måttligt men inte försumbart. Sammanfattningsvis kommer dessa förfiningar av den elektriska stimuleringstekniken att tillåta en mer detaljerad bedömning av viljemässig aktivering och förekomsten av nedsatt central aktiveringsförmåga. Resultaten att unga och gamla, friska aktiva personer kan uppnå en mycket hög viljemässig aktivering av sin lårmuskulatur kommer att förbättra tolkningen av bedömningar av viljemässig aktivering och förekomsten av nedsatt central aktiveringsförmåga hos patienter. Resultaten från skattningen av obehag gör att vi kan förbättra informationen som lämnas till patienter i studier av viljemässig aktivering och förekomsten av nedsatt central aktiveringsförmåga. (Less)
Abstract
The evaluation of skeletal muscle strength is an important part of the physiotherapist’s clinical examination in order to plan and execute appropriate interventions. This requires the objective assessment of muscle strength and the determination of the underlying factors of muscle weakness. One factor that can contribute to muscle weakness is the inability of the central nervous system to voluntarily recruit and optimally activate the alpha motor neurons. A sub-optimal voluntary activation (VA) is termed central activation failure (CAF). A common way to assess VA and to detect and quantify CAF is to superimpose an electrical stimulus over the motor nerve to the muscle during a maximal voluntary contraction (MVC). If the stimulus augments... (More)
The evaluation of skeletal muscle strength is an important part of the physiotherapist’s clinical examination in order to plan and execute appropriate interventions. This requires the objective assessment of muscle strength and the determination of the underlying factors of muscle weakness. One factor that can contribute to muscle weakness is the inability of the central nervous system to voluntarily recruit and optimally activate the alpha motor neurons. A sub-optimal voluntary activation (VA) is termed central activation failure (CAF). A common way to assess VA and to detect and quantify CAF is to superimpose an electrical stimulus over the motor nerve to the muscle during a maximal voluntary contraction (MVC). If the stimulus augments torque, then a CAF may be inferred. The overall objectives of this thesis were: i) to develop the methodology of the superimposed electrical stimulation technique; ii) to use the technique to assess the degree of voluntary activation during isometric knee extension in healthy, moderately active, young and older women and men; and iii) to evaluate the degree of discomfort caused by the superimposed electrical stimulation technique. Two methodological studies were performed using a model of CAF whereby the subjects were stimulated at 80% MVC of the knee extensors. The effects of the stimuli on torque increment size, the variability of torque increment size and the perceived discomfort from the stimuli were assessed. Discomfort was assessed using a 100 mm visual analogue scale for pain (VAS-pain). The main findings were that a pulse train stimulus at 100 Hz was superior to single impulses to illicit torque increments during high levels of voluntary action and should be the preferred stimulus mode to study VA. There was no difference in the size of the torque increments when pulse trains of lengths 100 ms, 200 ms or 300 ms were used or when pulse trains at 150 V and 200 V were used. Pulse trains of 100 ms length gave rise to less variability in the torque increment size than trains of 50 ms, but the discomfort from 100 ms trains was somewhat greater than from 50 ms trains. Pulse durations of 0.1 ms and 0.2 ms gave similar torque increments, but pulse durations of 0.1 ms induced significantly less discomfort at sub-maximal effort. The results from the VA assessments of healthy, young women and showed that they have the ability to fully voluntarily activate the knee extensors isometrically, but not on every attempt. Older men achieved very high VA levels, similar to those of the younger men. Older women displayed a slightly lower level of VA and some of the older women never achieved full voluntary activation on any attempt. The mean score of perceived discomfort during 100% MVC was 35 mm for the young women and men and 40 mm for the older women and men. These findings indicate that, with the electrical stimulation parameters used (pulse trains 100 Hz, 100 ms length, pulse duration 0.1 ms or 0.2 ms, 150 V), the level of discomfort was generally moderate and tolerable but not negligible. In conclusion, these developments of the superimposed electrical stimulation technique will allow a more detailed and adequate assessment of VA and CAF. The findings of very high VA levels (>97%) in healthy, active, young and old women and men will aid the interpretation of VA assessments in patients. The results from the discomfort evaluations will assist the researcher or clinician to better inform future patients about the general level of discomfort to be expected from assessments using the superimposed electrical stimulation technique. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Sundelin, Gunnevi, Samhällsmedicine och rehabilitering, Umeå Universitet
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Physical medicine, pain measurement, electric stimulation, muscle, kinesitherapy, revalidation, rehabilitation, Rehabilitering (medicinsk och social)
pages
104 pages
publisher
Michael Miller, Department of Physical Therapy, Lasarettsgatan 7, 221 85 Lund, Sweden,
defense location
Auditoriet, Kulturen, Lund
defense date
2004-10-22 10:15
ISBN
91-628-6256-1
language
English
LU publication?
yes
id
1e803cb4-aea8-4dc5-bf21-43ff47a6f6ce (old id 467403)
date added to LUP
2007-09-25 14:09:51
date last changed
2016-09-19 08:45:11
@misc{1e803cb4-aea8-4dc5-bf21-43ff47a6f6ce,
  abstract     = {The evaluation of skeletal muscle strength is an important part of the physiotherapist’s clinical examination in order to plan and execute appropriate interventions. This requires the objective assessment of muscle strength and the determination of the underlying factors of muscle weakness. One factor that can contribute to muscle weakness is the inability of the central nervous system to voluntarily recruit and optimally activate the alpha motor neurons. A sub-optimal voluntary activation (VA) is termed central activation failure (CAF). A common way to assess VA and to detect and quantify CAF is to superimpose an electrical stimulus over the motor nerve to the muscle during a maximal voluntary contraction (MVC). If the stimulus augments torque, then a CAF may be inferred. The overall objectives of this thesis were: i) to develop the methodology of the superimposed electrical stimulation technique; ii) to use the technique to assess the degree of voluntary activation during isometric knee extension in healthy, moderately active, young and older women and men; and iii) to evaluate the degree of discomfort caused by the superimposed electrical stimulation technique. Two methodological studies were performed using a model of CAF whereby the subjects were stimulated at 80% MVC of the knee extensors. The effects of the stimuli on torque increment size, the variability of torque increment size and the perceived discomfort from the stimuli were assessed. Discomfort was assessed using a 100 mm visual analogue scale for pain (VAS-pain). The main findings were that a pulse train stimulus at 100 Hz was superior to single impulses to illicit torque increments during high levels of voluntary action and should be the preferred stimulus mode to study VA. There was no difference in the size of the torque increments when pulse trains of lengths 100 ms, 200 ms or 300 ms were used or when pulse trains at 150 V and 200 V were used. Pulse trains of 100 ms length gave rise to less variability in the torque increment size than trains of 50 ms, but the discomfort from 100 ms trains was somewhat greater than from 50 ms trains. Pulse durations of 0.1 ms and 0.2 ms gave similar torque increments, but pulse durations of 0.1 ms induced significantly less discomfort at sub-maximal effort. The results from the VA assessments of healthy, young women and showed that they have the ability to fully voluntarily activate the knee extensors isometrically, but not on every attempt. Older men achieved very high VA levels, similar to those of the younger men. Older women displayed a slightly lower level of VA and some of the older women never achieved full voluntary activation on any attempt. The mean score of perceived discomfort during 100% MVC was 35 mm for the young women and men and 40 mm for the older women and men. These findings indicate that, with the electrical stimulation parameters used (pulse trains 100 Hz, 100 ms length, pulse duration 0.1 ms or 0.2 ms, 150 V), the level of discomfort was generally moderate and tolerable but not negligible. In conclusion, these developments of the superimposed electrical stimulation technique will allow a more detailed and adequate assessment of VA and CAF. The findings of very high VA levels (>97%) in healthy, active, young and old women and men will aid the interpretation of VA assessments in patients. The results from the discomfort evaluations will assist the researcher or clinician to better inform future patients about the general level of discomfort to be expected from assessments using the superimposed electrical stimulation technique.},
  author       = {Miller, Michael},
  isbn         = {91-628-6256-1},
  keyword      = {Physical medicine,pain measurement,electric stimulation,muscle,kinesitherapy,revalidation,rehabilitation,Rehabilitering (medicinsk och social)},
  language     = {eng},
  pages        = {104},
  publisher    = {ARRAY(0x89c1130)},
  title        = {Voluntary activation of skeletal muscle in young and old women and men},
  year         = {2004},
}