Bilateral Limb Phase Relationship and Its Potential to Alter 2 Muscle Activity Phasing During Locomotion

28 It is well established that the sensorimotor state of one limb can influence another limb 29 and therefore, bilateral somatosensory inputs make an important contribution to interlimb 30 coordination patterns. However, the relative contribution of interlimb pathways for modifying 31 muscle activation patterns in terms of phasing is less clear. 32 Here we studied adaptation of muscle activity phasing to the relative angular positions of 33 limbs using a split-crank ergometer, where the cranks could be decoupled to allow different 34 spatial angular position relationships. Twenty neurologically healthy individuals performed the 35 specified pedaling tasks at different relative angular positions while surface EMG signals were 36 recorded bilaterally from eight lower extremity muscles. During each experiment, the relative 37 angular crank positions were altered by increasing or decreasing their difference by randomly 38 ordered increments of 30° over the complete cycle (0o (in phase pedaling), 30o, 60o, 90o, 120o, 39 150o, 180o (standard pedaling), 210o, 240o, 270o, 300o, 330o out of phase pedaling). 40 We found that manipulating the relative angular positions of limbs in a pedaling task 41 caused muscle activity phasing changes that were either delayed or advanced, dependent on 42 the relative spatial position of the two cranks and this relationship is well-explained by a sine 43 curve. Further, we observed that the magnitude of phasing changes in bi-articular muscles (like 44 RF) was significantly greater than those of uni-articular muscles (like VM). These results are 45 important because they provide new evidence that muscle phasing can be systematically 46 influenced by interlimb pathways. 47