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Understanding Bilateral Deficit Phenomena: Neural Mechanisms and Interlimb Effects

This study investigates bilateral deficit (BD) in force production when one limb is activated, exploring its neural underpinnings. Previous literature highlights a decrease in maximal force during bilateral contractions of the contralateral limb, presenting a notable bilateral deficit. We conducted experiments on 22 males to examine variations in BD across different training backgrounds (weightlifters, cyclists, untrained subjects) and employed electromyography (EMG) to analyze muscle activation. Results indicate that neural mechanisms significantly influence BD, exhibiting both deficits and facilitation based on individual conditions.

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Understanding Bilateral Deficit Phenomena: Neural Mechanisms and Interlimb Effects

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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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