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Structure and function of the ankle dorsiflexor muscles in young healthy men and women

Drake, Anna Maria LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Det övergripande syftet med denna avhandling var att studera sambandet mellan skelettmuskulaturens struktur och funktion för att på sikt få ökade kunskaper om de bakomliggande mekanismerna vid muskulär svaghet och uttröttbarhet hos personer med olika skador eller sjukdomar. Mätningarna valdes att göras på musklerna på underbenets framsida, ankelns dorsalflexorer, dels som en modell för att studera sambandet mellan struktur och funktion, och dels för att denna muskelgrupp har en viktig betydelse för normal gångförmåga och balans. Delarbetenas syften var att i) utveckla metoder för att på ett tillförlitligt sätt mäta och utvärdera styrka, muskulär uttröttbarhet, muskelstorlek och muskelns... (More)
Popular Abstract in Swedish

Det övergripande syftet med denna avhandling var att studera sambandet mellan skelettmuskulaturens struktur och funktion för att på sikt få ökade kunskaper om de bakomliggande mekanismerna vid muskulär svaghet och uttröttbarhet hos personer med olika skador eller sjukdomar. Mätningarna valdes att göras på musklerna på underbenets framsida, ankelns dorsalflexorer, dels som en modell för att studera sambandet mellan struktur och funktion, och dels för att denna muskelgrupp har en viktig betydelse för normal gångförmåga och balans. Delarbetenas syften var att i) utveckla metoder för att på ett tillförlitligt sätt mäta och utvärdera styrka, muskulär uttröttbarhet, muskelstorlek och muskelns sammansättning av muskelvävnad och annan vävnad, ii) utvärdera olika statistiska variabler för att bedöma test-retest reliabilitet, iii) undersöka faktorer som kan förklara variationer i styrka och muskelstorlek, och iv) studera eventuella könsskillnader i muskelstruktur och muskelfunktion. Försökspersonerna utgjordes av unga friska män och kvinnor i åldern 20 till 32 år med en likartad fysisk aktivitetsnivå. I de tre första delarbetena utarbetades metoder för att mäta maximal koncentrisk och excentrisk styrka samt uttröttbarhet i fotledens dorsalflexorer. Mätningarna gjordes i en isokinetisk styrkemätningsutrustning (Biodex) och metodernas test-retest reliabilitet undersöktes. Resultaten visade att reliabiliteten för mätningarna var hög. I det fjärde delarbetet presenterades en metod för att med magnetisk resonanstomografi (MRI) undersöka human skelettmuskulatur. Metoden möjliggör en kvantifiering av tvärsnittsytan på en muskel eller muskelgrupp, samt en separation av muskelvävnad och annan vävnad (fett och bindväv). Mätningar av dorsalflexorernas storlek och sammansättning, gjorda på samma MR-bild, visade hög test-retest reliabilitet och god reproducerbarhet mellan två olika mätare. I det femte delarbetet studerades sambandet mellan dorsalflexorernas muskelstyrka och muskelstorlek samt eventuella könsskillnader. Trettio män och kvinnor med likartade fysiska aktivitetsmönster deltog i studien. Männen var starkare, både i koncentrisk och excentrisk styrka (≈ 24% respektive ≈ 27%; p<0.01) och hade större muskelstorlek jämfört med kvinnorna (19%; p<0.001). Fibertypsammansättningen i tibialis anterior, den viktigaste muskeln av ankelns dorsalflexorer, analyserades med biopsitagning och ett avancerat bildanalysprogram. Proportionen av typ I och typ II fibrer var likartad för män och kvinnor, medan fiberarean för typ I och typ II var större för män jämfört med kvinnor (21% respektive 31%; p<0.01). Multivariata analyser visade att muskelstorlek är den främsta enskilda faktor som förklarar variationerna i styrka (R2 = 53% till 81%) Fibertypsproportionen och kön (endast vid excentriska kontraktioner) bidrog också till variationerna, men till en mindre del (< 9%). Muskelstorleken visades till stor del bero på kroppsvikt och muskelfiberstorlek (R2 = 57%). Slutsatsen är att mätningar av styrka och uttröttbarhet i fotledens dorsalflexorer samt mätningar av dorsalflexorernas storlek och sammansättning har hög reliabilitet. Statistiska beräkningar av test-retest reliabilitet med kontinuerliga data bör inkludera en specificerad intra-klass korrelationskoefficient (ICC), beräkning av metodfelets storlek och en analys av eventuella systematiska fel. Det finns ett starkt samband mellan skelettmuskulaturens struktur och funktion hos unga och friska individer. Männens större förmåga att utveckla styrka i ankelns dorsalflexorer jämfört med kvinnor beror främst på skillnader i muskelstorlek som i sin tur är beroende på kroppsvikt och fiberstorlek. Den enda specifika könsskillnad som kunde påvisas var att män jämfört med kvinnor är starkare per ytenhet muskel i excentriska kontraktioner. Förklaringen till detta fenomen är oklart och kräver vidare studier. (Less)
Abstract
The overall aim of this thesis was to increase our knowledge of the relationship between structure and function of human skeletal muscle, and about factors affecting strength. The ankle dorsiflexor muscles (DF) were chosen as a representative model of human skeletal muscle, and because these muscles have important roles in gait and maintenance of balance. Specific aims in this thesis were: i) to develop reliable methods to assess DF structure and function, ii) to examine several statistical measures for the interpretation of test-retest reliability, iii) to investigate determinants, and iv) potential sex-related differences, of DF strength and size. Young, healthy men and women between 20 and 32 years of age, with comparable physical... (More)
The overall aim of this thesis was to increase our knowledge of the relationship between structure and function of human skeletal muscle, and about factors affecting strength. The ankle dorsiflexor muscles (DF) were chosen as a representative model of human skeletal muscle, and because these muscles have important roles in gait and maintenance of balance. Specific aims in this thesis were: i) to develop reliable methods to assess DF structure and function, ii) to examine several statistical measures for the interpretation of test-retest reliability, iii) to investigate determinants, and iv) potential sex-related differences, of DF strength and size. Young, healthy men and women between 20 and 32 years of age, with comparable physical activity levels, participated in the five studies on which this thesis is based. Protocols to examine DF strength and fatigue using an isokinetic dynamometer (Biodex) were developed in studies I-III. The subjects performed three maximal concentric (CON) DF contractions at five angular velocities (study I), three maximal eccentric (ECC) DF contractions at two angular velocities (study II), and 50 consecutive maximal CON DF contractions at 60°/s (study III), on two different occasions separated by 7-10 days. Intra-rater test-retest reliability of muscle strength and fatigue measurements was highly reliable. In study IV, measurements of DF contractile and noncontractile components were obtained using magnetic resonance imaging (MRI), and intra- and inter-rater test-retest reliability for repeated measurements from the same MR-image was examined and found to be highly reliable. Several statistical indices of test-retest reliability were used in studies I-IV. In study V, determinants and potential sex-related differences of DF strength and size were assessed in 30 men and women with comparable physical activity levels. Men had higher isokinetic DF CON and ECC strength (≈24% and ≈27%; p<0.01), and larger DF contractile cross-sectional area (cCSA: 19%; p<0.001), than women. Biopsies from the tibialis anterior muscle, the main DF, were prepared enzyme histochemically to determine areas (AREA) and proportions (PROP) of types I and II fibres. Men had larger AREA I and AREA II (21% and 31%; p<0.01) than women, whereas PROP I was similar between the sexes. Multivariate linear regression revealed that CON DF strength was up to 72% determined by cCSA and PROP I, and ECC DF strength was up to 81% determined by cCSA, PROP I and sex. For both CON and ECC DF strength, variables other than cCSA explained at most 9% of the variation. Body weight and fibre areas explained more than 50% of the variation in cCSA. In conclusion, test-retest reliability of DF strength and fatigue measurements, and assessments of DF tissue components, were highly reliable. Test-retest reliability based on continuous data is best analysed with several statistical indices – a specified ICC, method error statistics and analyses of systematic change in the mean. The structure and function of the DF in young, healthy individuals were closely related. The greater strength in men was almost exclusively explained by the greater muscle size, which, in turn, was determined by differences in body weight and fibre areas. Sex-specific difference existed in the ECC mode – when muscle size and physical activity levels were accounted for men produced more ECC torque for the same amount of muscle. This sex-specific difference is unclear and requires further study. (Less)
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author
opponent
  • Professor Jansson, Eva, Avd för Klinisk Fysiologi, Huddinge Sjukhus, 141 86 Huddinge
organization
publishing date
type
Thesis
publication status
published
subject
keywords
kinesitherapy, revalidation, rehabilitation, Rehabilitering (medicinsk och social), Physical medicine, reproducibility of results, muscle fibres, magnetic resonance imaging, isokinetic strength, skeletal muscle, Ankle joint
pages
115 pages
publisher
Anna Maria Holmbäck, Department of Physical Therapy, University Hospital, SE-221 85 Lund, Sweden,
defense location
University Hospital, Lund, Sweden
defense date
2002-10-25 10:15
ISBN
91-628-5377-5
language
English
LU publication?
yes
id
1dd79e11-a4ea-440c-b549-948a1c4c7754 (old id 465004)
date added to LUP
2007-09-27 15:43:32
date last changed
2016-09-19 08:45:14
@phdthesis{1dd79e11-a4ea-440c-b549-948a1c4c7754,
  abstract     = {The overall aim of this thesis was to increase our knowledge of the relationship between structure and function of human skeletal muscle, and about factors affecting strength. The ankle dorsiflexor muscles (DF) were chosen as a representative model of human skeletal muscle, and because these muscles have important roles in gait and maintenance of balance. Specific aims in this thesis were: i) to develop reliable methods to assess DF structure and function, ii) to examine several statistical measures for the interpretation of test-retest reliability, iii) to investigate determinants, and iv) potential sex-related differences, of DF strength and size. Young, healthy men and women between 20 and 32 years of age, with comparable physical activity levels, participated in the five studies on which this thesis is based. Protocols to examine DF strength and fatigue using an isokinetic dynamometer (Biodex) were developed in studies I-III. The subjects performed three maximal concentric (CON) DF contractions at five angular velocities (study I), three maximal eccentric (ECC) DF contractions at two angular velocities (study II), and 50 consecutive maximal CON DF contractions at 60°/s (study III), on two different occasions separated by 7-10 days. Intra-rater test-retest reliability of muscle strength and fatigue measurements was highly reliable. In study IV, measurements of DF contractile and noncontractile components were obtained using magnetic resonance imaging (MRI), and intra- and inter-rater test-retest reliability for repeated measurements from the same MR-image was examined and found to be highly reliable. Several statistical indices of test-retest reliability were used in studies I-IV. In study V, determinants and potential sex-related differences of DF strength and size were assessed in 30 men and women with comparable physical activity levels. Men had higher isokinetic DF CON and ECC strength (≈24% and ≈27%; p&lt;0.01), and larger DF contractile cross-sectional area (cCSA: 19%; p&lt;0.001), than women. Biopsies from the tibialis anterior muscle, the main DF, were prepared enzyme histochemically to determine areas (AREA) and proportions (PROP) of types I and II fibres. Men had larger AREA I and AREA II (21% and 31%; p&lt;0.01) than women, whereas PROP I was similar between the sexes. Multivariate linear regression revealed that CON DF strength was up to 72% determined by cCSA and PROP I, and ECC DF strength was up to 81% determined by cCSA, PROP I and sex. For both CON and ECC DF strength, variables other than cCSA explained at most 9% of the variation. Body weight and fibre areas explained more than 50% of the variation in cCSA. In conclusion, test-retest reliability of DF strength and fatigue measurements, and assessments of DF tissue components, were highly reliable. Test-retest reliability based on continuous data is best analysed with several statistical indices – a specified ICC, method error statistics and analyses of systematic change in the mean. The structure and function of the DF in young, healthy individuals were closely related. The greater strength in men was almost exclusively explained by the greater muscle size, which, in turn, was determined by differences in body weight and fibre areas. Sex-specific difference existed in the ECC mode – when muscle size and physical activity levels were accounted for men produced more ECC torque for the same amount of muscle. This sex-specific difference is unclear and requires further study.},
  author       = {Drake, Anna Maria},
  isbn         = {91-628-5377-5},
  keyword      = {kinesitherapy,revalidation,rehabilitation,Rehabilitering (medicinsk och social),Physical medicine,reproducibility of results,muscle fibres,magnetic resonance imaging,isokinetic strength,skeletal muscle,Ankle joint},
  language     = {eng},
  pages        = {115},
  publisher    = {Anna Maria Holmbäck, Department of Physical Therapy, University Hospital, SE-221 85 Lund, Sweden,},
  school       = {Lund University},
  title        = {Structure and function of the ankle dorsiflexor muscles in young healthy men and women},
  year         = {2002},
}