Abstract Walking recovery is a top rehabilitation goal for many individuals with incomplete spinal cord injury (ISCI). Accordingly, there are extensive resources invested into understanding ISCI-induced walking impairments and developing interventions to advance recovery. While these efforts target lower extremity control, functional walking is a full-body activity requiring rhythmic, coordinated movements of the limbs and trunk. After ISCI, individuals often demonstrate trunk control deficits: aberrant trunk movements during stepping, impaired posture, and consequently, reliance on assistive devices and ongoing walking impairment. Despite the importance of the trunk in walking control, it is rarely an intervention target and clinical assessments of walking do not consider trunk control. Instead, trunk control is assessed in sitting or static standing, which provides limited insight into control during walking. Understanding of trunk control is critical to address the severe and persistent impairments that limit walking function. Our long-term objective is to quantify trunk control during walking to inform critical next steps in clinical assessment and future walking research. This initial study will quantify coordination of trunk movements and underlying muscle activation. We will address following aims: Aim 1: To test the hypothesis that individuals with ISCI demonstrate impaired coordination of trunk movements during walking. We predict individuals with ISCI will demonstrate reduced counter-rotational trunk movement across the gait cycle. The primary outcome will be the phase relationship between movements of the thorax and lower extremities, quantified by continuous relative Fourier phase, an established approach to quantify phase relationships during cyclic activities. Additionally, trunk kinematics (i.e., range of motion, accelerations) in all planes will be quantified and differences between those with ISCI and controls will be calculated. Aim 2: To test the hypothesis that individuals with ISCI demonstrate impaired intermuscular coordination of trunk and lower extremity muscles during walking. We predict that individuals with ISCI will demonstrate a reduced number of co-active muscle patterns to achieve the biomechanical sub-tasks of walking (i.e., limb loading, swing initiation). The primary outcome will be the number of motor modules (i.e., groups of consistently co-activated muscles) required to account for activation of 32 trunk and lower extremity muscles during walking. Additionally, timing of module activation and relative muscle contributions will be quantified. Achievement of these aims will address a critical gap in understanding walking control after ISCI. This 2-year study will provide initial evidence to develop larger, more definitive investigations of trunk control during walking, a critical step for advancement of research and care for people with ISCI.