# Perturbations During Gait on a Split-Belt Treadmill: A Scoping Review
## 3 Results
### Perturbations in the Anterior-Posterior (AP) Direction
#### 3.1.3 Characteristics of Perturbations  
Before perturbation, walking speeds were often set to participants' preferred speed--five studies [38; 39; 41; 42; 43] or specific values, such as 1 m/s [34; 40], 1.2 m/s [2; 33; 35], and 1.25 m/s [37; 44], to the rhythm of a metronome (slow--80 or fast--140 BPM) [36] or corresponding to a Froude number [30; 31; 32]. The timing of perturbations varied, with some occurring at fixed intervals: every 10 s [2; 4], every 15-20 s [38], or randomly [33; 36] every 10-15 strides [33]. Similar variability was observed for the length of each session and the number of perturbations. [PERSON], et al. [33] registered five trials, each containing 15 perturbations. [PERSON], et al. [36] had trials with four perturbations per leg. [PERSON], et al. [37] and [PERSON], et al. [39] induced 80 perturbations per participant. [PERSON], et al. [4] applied five perturbations for the three trials. The authors also varied in their methods of analyzing the parameters. In some cases, the results were based on responses to the first perturbation [4; 33; 36], while in others, they were obtained from the average of all trials containing responses to the perturbations [2; 30; 31; 34; 35]. Sometimes, the description was not clear [44]. Perturbations were most often triggered during heel strike, i.e., the IC phase. For slip-like perturbations, seven authors targeted only the IC phase [30; 31; 32; 33; 34; 35; 36]. [PERSON], et al. [4] considered perturbations in the IC, MS, and PSw phases. [PERSON], et al. [37] set the onset of belt accelerations at 10%, 15%, 20%, and 30% of the gait cycle. For trip-like perturbations, all three papers [19; 38; 39] targeted only the IC phase with one-belt deceleration. Among studies considering both slip- and trip-like perturbations, four authors chose only perturbations in the IC phase. [PERSON], et al. [41] specified perturbations in the PSw phase, while [PERSON] and [PERSON] [2] analyzed perturbations in the IC, MS, and PSw phases. The duration and intensity of perturbations varied based on equipment. Authors using the Sensly treadmill [30; 31; 32] set perturbation intensity with a Froude number of 0.1 to 0.4 and an acceleration of 8 m/s\({}^{2}\) for a slip-like effect. There was no information about their duration. For the Grail Motek, perturbation magnitude ranged from 1 (0.1 m/s speed change) to 5 (0.5 m/s speed change) [2; 4; 33]. [PERSON], et al. [4] reported a slip-like perturbation lasting 0.82 s, with speed changing from 1.2 to 1.7-1.8 m/s, then back to 1.2 m/s. [PERSON], et al. [37] used the Caren Motek system to accelerate from 1.25 to 2.5 m/s and back, with a 15 m/s\({}^{2}\) acceleration/ deceleration over 340 ms (30% of the gait cycle). [PERSON], et al. [34] used the M-Gait Motek to accelerate belts to 0.35 m/s, then return to regular speed, with perturbation lasting up to 0.5 s. [PERSON], et al. [36] applied a Bertec treadmill acceleration of 1.6 m/s at 5.3 m/s\({}^{2}\) for 0.3 s, then decelerated to 0 m/s at 5.3 m/s\({}^{2}\) for 0.3 s, with a GRF threshold of 5 N on the slipping side. Two authors described a trip-like perturbations setting. [PERSON], et al. [39] used the Bertec treadmill to slow the belt by an increment of 0 to 0.4 m/s during walking. [PERSON], et al. [19] set the Caren Motek system to decelerate the belt to 0.5 m/s for 0.5 s with a maximum acceleration of 3 m/s\({}^{2}\), then to rapidly accelerate back to the baseline speed. In the papers investigating both slip- and trip-like perturbations, the settings varied significantly. [PERSON], et al. [40] used a Woodway treadmill to apply perturbations lasting 50 ms, with forward accelerations of +20 m/s\({}^{2}\) (velocity +2 m/s) and +40 m/s\({}^{2}\) (velocity +3 m/s) and backward accelerations of \(-\)20 m/s\({}^{2}\) (0 m/s) and \(-\)40 m/s\({}^{2}\) (\(-\)1 m/s). [PERSON], et al. [41] set the Bertec treadmill to decelerate at \(-\)10 m/s\({}^{2}\) for trips and accelerate at 20 m/s\({}^{2}\) for slips. [PERSON] et al.