Introduction  Maximal 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)

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): , 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?

Subjects  22 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)

Methods  R and L knee extension (1100) and L elbow flexion (900) max force  Supine position with either arm/leg or leg/leg isometric contractions

Apparatus  E-stim - four 3x6 electrodes over R quads  EMG - bipolar electrodes over belly of VL and BF of R leg  EMG - over biceps and triceps of L arm

Protocol  All 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 Analysis  Bilateral Index (BI) = [100 x (bilateral)] RU+LU  Leg/leg & arm/leg BI for force (BIf) and EMG (BIe)  EMG filtered and rectified  Force from single max repetition

EMG Analysis (typical) Force EMG Filter L onlyR onlyBilateral

Exp. 1 Results  Leg/leg task exhibited  WL BI f = % ^ / BI e = % ^  CY BI f = % * / BI e = % * ^  UN BI f = % * ^ / BI e = %

Exp. 1 Results Cont... Arm/leg task exhibited WL BI f = % / BI e = % CY BI f = % / BI e = % UN BI f = % / BI e = %

Exp. 2 Results 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 BDBFNull

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/Bi e ? leg data EMG & 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

Electromyostimulation  E-stim of contralateral limb causes  facilitation of MVC  Subjects were unable to voluntarily exert maximal force  Neural integration from contralateral feedback causes facilitation  Amount of facilitation mediated by BD or BF group

Conclusions  BD is a local neural phenomenon that is influenced by afferent feedback  BD exhibition depends on neural integration between peripheral and central sources

Related Investigations  BD 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 image 2 Within hemis 3 Non-homol in diff hemis (model by Archontides, 1992) Related Investigations

Future Research  Include females  Perform dynamic movements  Change velocities  Monitor EMG from whole muscle group  Pair different limbs