introduction maximal force is decreased when the homologous contralateral limb is activated ...
TRANSCRIPT
IntroductionMaximal force is decreased when the
homologous contralateral limb is activated
Recognized for a century (Mosso, 1892)Bilateral deficit (BD, Ohtsuki 1983)
occurs with maximum voluntary bilateral activation of contralateral limb muscles
BD = bilateral force < sum of unilateral
Literature Review Ohtsuki, grip strength finger max unilat (1981) Isometric vs. dynamic contractions with males
Coyle, DKE no change w/velocity, (1981) Vandervoort, DLP increase in BD w/vel, (1984) Secher, ILP no change with angle, (1988) Schantz, IKE facilitation , (1989)
EMG decline vs. no-decline Vandervoort, decline with BD increase (1984) Schantz, no decline with BD (1989)
Literature Review Cont... Fast vs slow twitch muscle fibers Vandervoort, DLP, (FT) (1984) Grabiner, IKE, (FT) rate of torque (1993) Secher, ILP, (ST) pharmacological (1978) Brown, DKE, (ST) BD & vel (1994)
-20
-15
-10
-5
0
5
BD%
60 120 180 240 360
Velocity
ExtFlex
Literature Review Cont... Facilitation = bilateral force > sum of
unilateral Homologous facilitation maximally (Brown,
1994) Nonhomologous facilitation sub-maximally
w/speech and finger amplitude (Kelso, Tuller and Harris, 1983)
Limited resources or inability to activate?
Maximum Bilateral Contractions Are Modified By Neurally Mediated Interlimb Effects
J.D. Howard and R.M. Enoka, J. Appl. Physiol. 70(1): 306-316, 1991.
Purpose Is BD due to neural mechanisms?Does EMG decline during BD? Is BD exhibited with nonhomologous
muscles?Does the effect of e-stim on
contralateral limb differ between subjects with different degrees of BD?
Subjects22 males (19 to 39 yrs of age)2 experiments (18 in exp. 1 & 12 in exp.
2)Exp. 1 (3 groups of 6 )
weightlifters (WL) (1 year bilateral) cyclists (CY) (1 year competition) untrained (UN) (no training)
Exp. 2 (all subjects naive)
MethodsR and L knee extension (1100) and L
elbow flexion (900) max forceSupine position with either arm/leg or
leg/leg isometric contractions
ApparatusE-stim - four 3x6 electrodes over R
quadsEMG - bipolar electrodes over belly of
VL and BF of R legEMG - over biceps and triceps of L arm
ProtocolAll trials - 3s max force with 30s rest
(1:10)Exp. 1 - unil and bilat max L & R knee
ext and max R elbow flex Exp. 2
- max R knee - max L knee w/ R leg e-stim - max L knee w/o R leg
Data AnalysisBilateral Index (BI) =
[100 x (bilateral)] - 100
RU+LULeg/leg & arm/leg BI for force (BIf) and
EMG (BIe)EMG filtered and rectifiedForce from single max repetition
Exp. 1 ResultsLeg/leg task exhibited
WL BIf = +6.2+4.7% ^ / BIe= +13.7+12.0% ^ CY BIf = -6.6+7.1% * / BIe= -11.5+4.9% * ^ UN BIf = -9.5+6.8% * ^ / BIe= +1.2+22.9%
0
200
400
600
800
1000
1200
1400
N
WL CY UN
FORCE
LL BiRR Bi
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
N
WL CY UN
EMG
LL BiRR Bi
Exp. 1 Results Cont...•Arm/leg task exhibited
WL BIf = -6.9+8.0% / BIe= -0.3+4.1%CY BIf = -1.4+15.1% / BIe= -11.7+11.3%UN BIf = -4.8+7.5% / BIe= -7.1+16.3%
0
200
400
600
800
1000
1200
1400
N
WL CY UN
FORCE
ArmBiLegBi
Exp. 2 Results
-9.7-4.2
42
6.2 5.8
25.5
54.6
16.2
-10
0
10
20
30
40
50
60
N
Deficit Facilitation
BI forceBI emgR ELL FL
• 2 groups (n=6) either deficit or facilitation•L leg MVC (w or w/o) R leg e-stim
• L leg EMG was equal w or w/o R leg e-stim
Discussion BD is reliable for untrained subjects BD is not always present in trained subjects Some subjects exhibit facilitation Interlimb interactions exist on a continuum
BD BFNull
Purpose Is BD due to neural mechanisms?Does EMG decline during BD? Is BD exhibited with nonhomologous
muscles?Does the effect of e-stim on
contralateral limb differ between subjects with different degrees of BD?
Does EMG decline w/Bie?
• leg dataEMG & force = parallel
• r - EMG & force is variable
• EMG on only one muscle of quads
Nonhomologous Muscles BD? Inability to activate a large muscle
mass?Division of attention between arm/leg?BD not associated with nonhomologous
muscles
ElectromyostimulationE-stim of contralateral limb causes facilitation of MVCSubjects were unable to voluntarily
exert maximal forceNeural integration from contralateral
feedback causes facilitationAmount of facilitation mediated by BD
or BF group
ConclusionsBD is a local neural phenomenon that is
influenced by afferent feedbackBD exhibition depends on neural
integration between peripheral and central sources
Related InvestigationsBD is greatest in dominant limb
(Ohtsuki, 1983)BD is greater in paired proximal than
paired distal limbs (Asanuma, 1989)Specificity of BF to the limbs practiced
(Thorstensson, 1979)Multiple degrees of freedom act as a co-
ordinative structure (Kelso, 1979)
Homotopic inhibition of mirror image in motor cortex at high levels of activation, (Asanuma, 1962)
Inhibition:1 Mirror image2 Within hemis3 Non-homol in diff hemis (model by Archontides, 1992)
Related Investigations