Neuromuscular response of the trunk to sudden gait disturbances: Forward vs. backward perturbation

The study aimed to analyse neuromuscular activity of the trunk comparing four different perturbations during gait.Thirteen subjects (28 ± 3 yrs) walked (1 m/s) on a split-belt treadmill, while 4 (belt) perturbations (F1, F2, B1, B2) were randomly applied. Perturbations differed, related to treadmill belt translation, in direction (forward (F)/backward (B)) and amplitude (20 m/s2 (1)/40 m/s2 (2)). Trunk muscle activity was assessed with a 12-lead-EMG. EMG-RMS [%] (0–200 ms after perturbation; normalized to RMS of normal gait) was analyzed for muscles and four trunk areas (ventral left/right; dorsal left/right). Ratio of ventral:dorsal muscles were calculated. Muscle onset [ms] was determined. Data analysis was conducted descriptively, followed by ANOVA (post hoc Tukey-Kramer (α = 0.05)).All perturbations lead to an increase in EMG-RMS (428 ± 289%). F1 showed the lowest and F2 the highest increase for the flexors. B2 showed the highest increase for the extensors. Significant differences between perturbations could be observed for 6 muscles, as well as the 4 trunk areas. Ratio analysis revealed no significant differences (range 1.25 (B1) to 1.71 (F2) between stimuli. Muscle response time (ventral: 87.0 ± 21.7 ms; dorsal: 88.4 ± 17.0 ms) between stimuli was only significant (p = 0.005) for the dorsal muscles.Magnitude significantly influences neuromuscular trunk response patterns in healthy adults. Regardless of direction ventral muscles always revealed higher relative increase of activity while compensating the walking perturbations.