Fig. 1

A Step length values during a split belt treadmill trial. Step length values (red- left; blue-right; left ordinate) from a complete 10 min trial are depicted. This participant had more sever Parkinsonian signs on the right side of the body (‘worst side’). After two minutes of baseline walking (BL) with tied belts (TB), the speed of left belt was reduced by 50% (‘best side decrease’ – BSD; right ordinate). Gait asymmetry (GA) was exacerbated for the next 5 min of split belt walking more in the early adaptation phase (EA, e.g., 120–150 s) compared to the late adaptation (LA, e.g., 390–420 s’ – see also Fig. 2B). The trial ended with 3 more minutes of tied belt walking. It can be seen that GA was reversed in the early post adaptation stage (EPA, e.g., 420 – 450 s’), but the effect did not last and subsequently returned to resemble BL GA in late post adaptation (LPA). Big dots represent the averages of step lengths in each side, connected by a trend-line. None of these points contain mixed data from different belt conditions. Few right step length values are missing from the end of the trial due to technical problem. B Upper and lower limbs asymmetry at five epochs for four split-belt conditions (see methods for details). Upper panels correspond to early increase in gait asymmetry (GA) of baseline asymmetry by either decreasing the belt speed on the less-affected side (a; Best side decrease) or by increasing the belt speed on the more affected side (b; Worst side increase). The lower panels correspond to early increase in GA of baseline asymmetry towards the opposite direction by either decreasing the belt speed on the more affected side (c; Worst side decrease) or by increasing the belt speed on the less-affected side (d; Best side increase). Adaptation asymmetry in the upper limbs displayed a similar trend compared to lower limb GA, although non-significant for all comparisons (Wilcoxon signed rank test, p ≥ 0.051). Traces represent step length asymmetry for each participant (thin traces) as well as mean values (bold trace) and mean upper limbs asymmetry (dashed traces). BL – baseline, EA – early adaptation, LA – late adaptation, EPA – early post-adaptation, LPA – late post-adaptation