The Bilateral Limb Deficit (BLD) Phenomenon During Leg Press: An Investigation Into Central And Peripheral Factors

Abstract Background: The bilateral limb deficit (BLD) phenomenon is the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. It has been suggested that the BLD may be due to interhemispheric inhibition, however the origin of the deficit is yet to be determined. The aim of this study was to investigate central and peripheral factors responsible for the BLD during leg press using surface electromyography (EMG) and electroencephalography (EEG). Methods: Fourteen adults (age = 23.7 ± 4.7 years old) completed bilateral (BL), unilateral left (UL) and unilateral right (UR) isometric leg press exercises. Bilateral limb ratio (BLR) was calculated similar to previous studies and surface EMG from three muscles of the quadriceps femoris (vastus lateralis, vastus medialis and rectus femoris) were used to compare signal amplitude in each condition. Movement related cortical potentials (MRCPs) over the left and right motor cortex areas (C3 and C4, respectively) were used to assess brain activity asymmetries reflecting central factors. Results: The BLD was present in ten of the fourteen participants (mean BLR=81.4%). Mean RMS activity demonstrated differences in amplitudes between the quadriceps muscles, however no significant differences were noted between bilateral and unilateral conditions. No significant differences in MRCPs were observed between brain activity of the C3 and C4 electrodes in any of the conditions. Conclusion: This study noted the presence of BLD however the results did not provide evidence of significant limitations in either the EMG and EEG data.