# Perturbations During Gait on a Split-Belt Treadmill: A Scoping Review
## 3 Results
### Perturbations in the Mediolateral (ML) Direction
#### 3.2.3 Characteristics of Perturbations  
Before perturbation, walking speeds were typically set to participants' preferred speeds in six studies [9; 48; 51; 53; 56; 59] or specific values: 0.41 m/s [52], 0.78 \(\pm\) 0.19 m/s [58], 0.89 \(\pm\) 0.12 m/s [54], 1 m/s [55], 1.1 m/s [47], 1.22 \(\pm\) 0.28 m/s [46], and 1.25 m/s [49]. [PERSON], et al. [50] used different preferred speeds for young and older participants (1.27 \(\pm\) 0.13 m/s vs. 1.45 \(\pm\) 0.16 m/s). Similar to the studies in Table 1, perturbations were most frequently applied only during the IC phase of gait, as observed in seven studies. In the first group, there was one paper [51]. In the second, there were four papers [9; 52; 54; 55], and in the third, there were two [57; 58]. Some authors did not specify when the perturbation occurred [46; 49; 53; 59]. Perturbations were applied at various gait cycle moments in three papers from the first group [47; 48; 50] and one from the second group [56]. [PERSON], et al. [47] applied perturbations immediately after IC, during early and late MS (22.5%, 37.5% gait cycle), and PSw (52.5% gait cycle). Similarly, [PERSON], et al. [50] shifted the treadmill during the LR, TS, and MSw phases. [PERSON], et al. [48] induced perturbations randomly during single- or double-support phases. [PERSON], et al. [56] introduced perturbations at IC, MS, and PSw. Perturbations causing significant ML instability were typically administered in a pseudorandom or balanced random order. Most studies involved lateral shifts or oscillations of the treadmill platform, but the intensity and timing of these perturbations varied across studies. [PERSON], et al. [46] used the sum of four sine waves for perturbations, with participants completing trials of unperturbed and pseudorandom ML oscillations. [PERSON] and [PERSON] [49] programmed platform sways with sine wave patterns, limited to \(\pm\)0.05 m. [PERSON], et al. [51] applied 2.5 cm medial and lateral translations lasting 0.25 s during a single-leg stance. [PERSON], et al. [47] designed perturbations with three different magnitudes (small, medium, and large) and four directions (left/right translation, belt speed increase/decrease). [PERSON], et al. [48] implemented unannounced 15 cm platform shifts lasting 0.92 s. [PERSON], et al. [50] varied ML shifts to 1 cm, 3 cm, or 5 cm. Studies in the second group included additional AP displacements or combined ML and AP perturbations. [PERSON], et al. [52] applied ML and AP perturbations beginning 80-90 ms after IC, with ML displacements of 0.045 m and AP decelerations and accelerations at IC. [PERSON], et al. [54] triggered right-side perturbations at the IC with sudden forward or lateral movements. [PERSON] and [PERSON] [53] implemented a protocol involving perturbations during standing and walking, with various speeds for forward, backward, and lateral movements. [PERSON], et al. [55] investigated perturbed walking using four AP belt decelerations and four ML perturbations. In the case of the ML perturbation, the treadmill moved 5 cm in the opposite direction in 0.31 s, likely inducing a cross-stepping strategy. The AP disturbance caused the treadmill to decelerate by 9 m/s\({}^{2}\) for 0.12 s at the IC point. The order of perturbations, the perturbed leg, and the intervals between perturbations (10-60 s) were randomized but consistent for all participants. [PERSON], et al. [56] classified perturbations by direction, gait phase, and reference foot, using 15 cm ML displacements and 1.2 m/s AP decelerations. [PERSON], et al.