<p>The vestibulospinal and reticulospinal tracts play a crucial role in controlling lumbar erector spinae (LES). Electrical vestibular stimulation (EVS) can be used to investigate the contribution of the vestibular system in the control of a muscle during a motor task. A recent study observed a minimal contribution of the corticospinal projection to LES in a voluntary spine extension. We thus hypothesised a greater involvement of alternative pathways originating in the brainstem such as vestibulo- and reticulospinal tracts in the control of LES for this task. This study investigates the impact of EVS on the activation of LES during postural and voluntary tasks. Fifteen participants performed two motor tasks: a bilateral shoulder flexion (postural task) and a lumbar spine extension (voluntary task) during a simple precued reaction time (RT) paradigm. During the RT tasks, EVS was applied at three different timings (early, middle and late) within a pre-defined time window. Outcomes were (1) LES onset latencies elicited by the motor tasks and conditioned by EVS and (2) the central processing duration (CPD). EVS significantly reduced the onset latency of LES activation in both postural and voluntary tasks. The CPD was shorter for the postural compared to the voluntary task for the early and middle conditions. EVS shortens LES onset, suggesting a contribution of brainstem networks/tracts in both tasks. The shorter CPD for the postural task at early and middle timings compared to the voluntary task suggests an earlier contribution of the brainstem networks/tracts during the postural task. Further research is needed to elucidate the mechanisms and validate this paradigm.im</p>