Reflex activity of the lower leg muscles involved when compensating for falls has already been thoroughly investigated. However, the trunk’s role in this compensation strategy remains unclear. The purpose of this study, therefore, was to analyze the kinematics and muscle activity of the trunk during perturbed walking. Ten subjects (29±3 yr;79±11 cm;74±14 kg) walked (1 m/s) on a split-belt treadmill, while 5 randomly timed, right-sided perturbations (treadmill belt deceleration: 40 m/s2) were applied. Trunk muscle activity was assessed with a 12-lead-EMG. Trunk kinematics were measured with a 3D-motion analysis system (12 markers framing 3 segments: upper thoracic area (UTA), lower thoracic area (LTA), lumbar area (LA)). The EMG–RMS [%] (0–200 ms after perturbation) was analyzed and then normalized to the RMS of normal walking. The total range of motion (ROM;[°]) for the extension/flexion, lateral flexion and rotation of each segment were calculated. Individual kinematic differences between walking and stumbling [%; ROM] were also computed. Data analysis was conducted descriptively, followed by one- and two-way ANOVAs (α¼ 0.05).
Stumbling led to an increase in ROM, compared to unperturbed gait, in all segments and planes. These increases ranged between 107±26% (UTA/rotation) and 262±132% (UTS/lateral flexion), significant only in lateral flexion. EMG activity of the trunk was increased during stumbling (abdominal: 665±283%; back: 501±215%), without significant differences between muscles.
Provoked stumbling leads to a measurable effect on the trunk, quantifiable by an increase in ROM and EMG activity, compared to normal walking. Greater abdominal muscle activity and ROM of lateral flexion may indicate a specific compensation pattern occurring during stumbling.