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Introduction

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.

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Introduction

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  1. 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

  2. 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)

  3. 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)

  4. 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?

  5. 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.

  6. 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?

  7. 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)

  8. 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

  9. 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

  10. 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

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

  12. EMG Analysis (typical) L only Bilateral R only Force EMG Filter

  13. Exp. 1 Results • Leg/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%

  14. 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%

  15. 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

  16. BD Null BF 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

  17. 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?

  18. Does EMG decline w/Bie? • leg data • EMG & force • = parallel • EMG on • only one • muscle of • quads • r - EMG & force • is variable

  19. Nonhomologous Muscles BD? • Inability to activate a large muscle mass? • Division of attention between arm/leg? • BD not associated with nonhomologous muscles

  20. 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

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

  22. 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)

  23. Related Investigations Homotopic inhibition of mirror image in motor cortex at high levels of activation, (Asanuma, 1962) • Inhibition: • Mirror image • Within hemis • Non-homol in diff • hemis (model by • Archontides, 1992)

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

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