- Email: [email protected]
EMG indicators of abdominal muscle structure and function during pregnancy
Abstracts-International
Society of Biomechanics XIV Congress 1993
EMG INDICATORS OF ABDOMINAL MUSCLE STRUCTURE AND FUNCTION DURING PREGNANCY yendy L. GiIIeard* and J. Mark M. Brown# Faculty of Health Sciences,The University of Sydney, Lidcombe 2141, Australia # The University of Wollongong, WoIlongong, 2500, Australia The structureandfunctionof the abdominalmusclesduringpregnancyandthe immediatepost-birthperiodwas investigatedusingelectromyography (EM@. Six prhnlgravidasubjectswith a singlefoetus(maternalgroup) participatedin ninetestsessionsfrom 14 weeksgestationto eightweekspost-birth.Ten nulliparousuniversitystudents (controlgroup)participatedin four testsessionsat intervalsof four weeks.SurfaceEMG from upperandlower RA, andExternalOblique(EO) wererecordedat rest,andduringa supinemaximalisometriccontra&n. ‘Ihe integrated EMG (IFMG) andmeanfrequency0 werecalculated.The IEMG for eachelectrodenair wasthenexoressed asa percentage of the total IEMd (rel&MG). Skinfoldsweremeasuredat eachsite. Therewasno signific& variationin maternalgroupIEMG at restandskinfoldsizeaspregnancyprogressed.No significantvariationin controlgrouprelIEMG andMF was foundfrom testto test. As pregnancyprogressed, maternalgrouprel-IEMGincreasedsignificantly (1~0.05)for upuezRA anddecreased for EO. The MF for UDIXZRA. lower RA andEO. showedno sieniticantchange. The rel&MG‘<s of this studyindicatefor a supinemax&um i&metric contractiontherewasa relitive increase~n upperRA anddecreasein EO muscleactivity aspregnancyprogressed. which wasreversedpost-birth.Thesevariations werenot thoughtto be dueto signaldecrementby additionaladiposetissueor from backgroundnoise. As MF is related to musclefibre diameter,theresultsindicatethatthe musclefibre diameterswerenot altered.The variationsin relIEMG arethereforethoughtto be theresultof alteredmusclefunctionalinter-relationships aspregnancyprogressed. This maybe dueto grossanatomicalchangesin the trunk whichalterthe line of actionof the abdominalmuscles,or an alteredmovementpatterndueto the impedance of theenlargingabdominaldimensions.
Effects of disuse by lower limb immobiliition
in healthy men
Albert Gollhofer, Bemd Mey. Christoph Schcuffelcn,Walter Rapp institute for Sport Sciences.University of Frciburg, D-7800 Freiburg, Germany
Similarily to adaptationin strengthtraining the effectsof prolongeddisusecan be attributed either to neuronaladaptationsor changesin the contractilesystem.In the presentstudy both voluntarily and reflexly generatedactivation was examinedin order to acquire a comprehensiveview about the neuromuscularconsequences.The right lower leg of the subjectwas immobilized by means of a plaster cast for ten days. The measureswere repeatedimmediately before and after immobilization as well as four and eight days afterwards.The latter examinationsshouid give someinformation about the recoveryof the disuseeffeets.Therelative reductionsin musclecrosssectional-areaof M. triceps s. was 12.9% (pKO.01) and 1.8% (n.s.) for the immobilized and non-immobiized leg, respectively. Isometric force was degradedby approximately 20% in the period 200 - 500 ms after contractiononset as well as in the MVC-condition. The force-values 100 ms after onset, however, remainedrather constant.Thesealterationswere also reflected in the IEMG of M. soleus: except for the tirst 100 ms intervall all EMGquantiti~ are suppressed after immobilization. While the IEMG increasedto initial values already four days after cast removal the recovery of the strengthabiity remainsuneompleteeven in the I-days mterval. The analysis of the stretch evoked Tnses reveztledthat .in both plantarflexors the stretch evoked responsesincreasedafter immobibzation. The overall behaviour, however, remained unchanged indicating a high relation between stretch velocity and BMG cespnse but no relation to the stretch amplitude. The initial values could be observedalready eight days afte-r cast removal. From the present data it can be concluded,that basic neuromuscularactivation mechanismsare affecte,i by disuse: neuronaldeficits are much fastercompensatedthan muscularalterations.
NEUROMUSCULAR FATIGUE DURING HEAVY RESISTANCE LOADING IN MEN AT DIFFERENT AGES Keijo HAkkinen Deuartment of Biology of Physical Activity, University of Jyviiskylii, Jyvgekyl& Finland _ Acute effects of heavy r&&ance loading on voluntary neural activation (integrated EMG). maximal isometric force. force-time and relax&ion time curvea of the leg extensor mwlee were examined in men at thrk different age group& i.e. young men (YM, ntii), 30 yeare (range 24 - 30): middle-aged men (MM, n=6), 50 yeara (range 44 - 52) and elderly men (a, n = 8), 70 ye= (ram13 66 - 75). The subjecta loaded their leg extensor mueeies by parfbiming 5 Seth in the bilahral leg extension ekreim on the mat&e (David 210) and peformed 10 re@tions in each set with the maximal load posnible (10 RM). The recovery time between the set8 was 3 minutas. The ioading in all groups.msulted in great decreaaeain maximal force in YM by 23.7 + 16.3 % (p < 0.05). in MM by33.6~8.6 % (p < 0.001) and in EMby 20.32 12.2 % (p c 0.001). The maximal rate of rise of force development decreesadin YbI hy 27.0 + 21.6 % (p < 0.01). in MM by 36.2 + 23.5 % (p < 0.01) and in EM by 26.5 + 11.0 % (p < 0.01). Considerable decreaseI occurrod both in the maximum avereged EMG and in the rate of rise of EMG of the loaded mwelee in Y’M (15.1 i 21.8 %; p < 0.05 end 12.1~ 16.9 %, p < 0.05) and in MM (5.0 2 13.6 %, ns. and 23.0 + 17.9 9b; p e 0.051. demonstrated .___,. while. EM -.. -.~~ ~~ ~~~ no decrease at all. The meen blood lactate concentration increeaed during the loading in YM up tn 11.5 2 3.7 (p < 0.001) in EM up to 9.6 + 2.5 (p < 0.001) end in EM up to 6.9 2 2.6 mmol x 1.’(p < 0.001). The present findings indicated that heavy resihance loading of the ne~omuscular system led in all age group8 to considerable acute fatigue in the contractile characteristics of the loaded muscles eccompenied in the young end middle-aged subjects by considerable fatigue also in the nervous system.
703
Society of Biomechanics XIV Congress 1993
EMG INDICATORS OF ABDOMINAL MUSCLE STRUCTURE AND FUNCTION DURING PREGNANCY yendy L. GiIIeard* and J. Mark M. Brown# Faculty of Health Sciences,The University of Sydney, Lidcombe 2141, Australia # The University of Wollongong, WoIlongong, 2500, Australia The structureandfunctionof the abdominalmusclesduringpregnancyandthe immediatepost-birthperiodwas investigatedusingelectromyography (EM@. Six prhnlgravidasubjectswith a singlefoetus(maternalgroup) participatedin ninetestsessionsfrom 14 weeksgestationto eightweekspost-birth.Ten nulliparousuniversitystudents (controlgroup)participatedin four testsessionsat intervalsof four weeks.SurfaceEMG from upperandlower RA, andExternalOblique(EO) wererecordedat rest,andduringa supinemaximalisometriccontra&n. ‘Ihe integrated EMG (IFMG) andmeanfrequency0 werecalculated.The IEMG for eachelectrodenair wasthenexoressed asa percentage of the total IEMd (rel&MG). Skinfoldsweremeasuredat eachsite. Therewasno signific& variationin maternalgroupIEMG at restandskinfoldsizeaspregnancyprogressed.No significantvariationin controlgrouprelIEMG andMF was foundfrom testto test. As pregnancyprogressed, maternalgrouprel-IEMGincreasedsignificantly (1~0.05)for upuezRA anddecreased for EO. The MF for UDIXZRA. lower RA andEO. showedno sieniticantchange. The rel&MG‘<s of this studyindicatefor a supinemax&um i&metric contractiontherewasa relitive increase~n upperRA anddecreasein EO muscleactivity aspregnancyprogressed. which wasreversedpost-birth.Thesevariations werenot thoughtto be dueto signaldecrementby additionaladiposetissueor from backgroundnoise. As MF is related to musclefibre diameter,theresultsindicatethatthe musclefibre diameterswerenot altered.The variationsin relIEMG arethereforethoughtto be theresultof alteredmusclefunctionalinter-relationships aspregnancyprogressed. This maybe dueto grossanatomicalchangesin the trunk whichalterthe line of actionof the abdominalmuscles,or an alteredmovementpatterndueto the impedance of theenlargingabdominaldimensions.
Effects of disuse by lower limb immobiliition
in healthy men
Albert Gollhofer, Bemd Mey. Christoph Schcuffelcn,Walter Rapp institute for Sport Sciences.University of Frciburg, D-7800 Freiburg, Germany
Similarily to adaptationin strengthtraining the effectsof prolongeddisusecan be attributed either to neuronaladaptationsor changesin the contractilesystem.In the presentstudy both voluntarily and reflexly generatedactivation was examinedin order to acquire a comprehensiveview about the neuromuscularconsequences.The right lower leg of the subjectwas immobilized by means of a plaster cast for ten days. The measureswere repeatedimmediately before and after immobilization as well as four and eight days afterwards.The latter examinationsshouid give someinformation about the recoveryof the disuseeffeets.Therelative reductionsin musclecrosssectional-areaof M. triceps s. was 12.9% (pKO.01) and 1.8% (n.s.) for the immobilized and non-immobiized leg, respectively. Isometric force was degradedby approximately 20% in the period 200 - 500 ms after contractiononset as well as in the MVC-condition. The force-values 100 ms after onset, however, remainedrather constant.Thesealterationswere also reflected in the IEMG of M. soleus: except for the tirst 100 ms intervall all EMGquantiti~ are suppressed after immobilization. While the IEMG increasedto initial values already four days after cast removal the recovery of the strengthabiity remainsuneompleteeven in the I-days mterval. The analysis of the stretch evoked Tnses reveztledthat .in both plantarflexors the stretch evoked responsesincreasedafter immobibzation. The overall behaviour, however, remained unchanged indicating a high relation between stretch velocity and BMG cespnse but no relation to the stretch amplitude. The initial values could be observedalready eight days afte-r cast removal. From the present data it can be concluded,that basic neuromuscularactivation mechanismsare affecte,i by disuse: neuronaldeficits are much fastercompensatedthan muscularalterations.
NEUROMUSCULAR FATIGUE DURING HEAVY RESISTANCE LOADING IN MEN AT DIFFERENT AGES Keijo HAkkinen Deuartment of Biology of Physical Activity, University of Jyviiskylii, Jyvgekyl& Finland _ Acute effects of heavy r&&ance loading on voluntary neural activation (integrated EMG). maximal isometric force. force-time and relax&ion time curvea of the leg extensor mwlee were examined in men at thrk different age group& i.e. young men (YM, ntii), 30 yeare (range 24 - 30): middle-aged men (MM, n=6), 50 yeara (range 44 - 52) and elderly men (a, n = 8), 70 ye= (ram13 66 - 75). The subjecta loaded their leg extensor mueeies by parfbiming 5 Seth in the bilahral leg extension ekreim on the mat&e (David 210) and peformed 10 re@tions in each set with the maximal load posnible (10 RM). The recovery time between the set8 was 3 minutas. The ioading in all groups.msulted in great decreaaeain maximal force in YM by 23.7 + 16.3 % (p < 0.05). in MM by33.6~8.6 % (p < 0.001) and in EMby 20.32 12.2 % (p c 0.001). The maximal rate of rise of force development decreesadin YbI hy 27.0 + 21.6 % (p < 0.01). in MM by 36.2 + 23.5 % (p < 0.01) and in EM by 26.5 + 11.0 % (p < 0.01). Considerable decreaseI occurrod both in the maximum avereged EMG and in the rate of rise of EMG of the loaded mwelee in Y’M (15.1 i 21.8 %; p < 0.05 end 12.1~ 16.9 %, p < 0.05) and in MM (5.0 2 13.6 %, ns. and 23.0 + 17.9 9b; p e 0.051. demonstrated .___,. while. EM -.. -.~~ ~~ ~~~ no decrease at all. The meen blood lactate concentration increeaed during the loading in YM up tn 11.5 2 3.7 (p < 0.001) in EM up to 9.6 + 2.5 (p < 0.001) end in EM up to 6.9 2 2.6 mmol x 1.’(p < 0.001). The present findings indicated that heavy resihance loading of the ne~omuscular system led in all age group8 to considerable acute fatigue in the contractile characteristics of the loaded muscles eccompenied in the young end middle-aged subjects by considerable fatigue also in the nervous system.
703