# Effects of Obesity on Adaptation Transfer from Treadmill to Over-Ground Walking
## 4 Discussion  
In the current study, we demonstrated that the temporal gait adaptation following split-belt treadmill walking was greater in adults with obesity versus adults with normal weight. We also found that a temporal gait adaptation following split-belt treadmill walking transfers to over-ground walking in both adults with obesity and adults with normal weight. The adaptation transfer of double-limb support time was smaller in adults with obesity when compared with the adults with normal weight. This provides additional support for the previous suggestion that gait characteristics such as lower step frequency and longer double-limb support phase exist in those with obesity. Throughout the adaptation, we observed that both groups successfully adapted their walking patterns to split-belt perturbations (adaptation), showed aftereffects (washout), and saved the memory of adapted walking patterns (re-adaptation), which is supported by previous research focusing on healthy young adults [16; 17; 22]. This is the first study, however, to demonstrate that adults with obesity adapted their walking and transferred from the treadmill to a real-world task: in this case, over-ground walking. In the current study, step length and double support asymmetries following split-belt treadmill adaptation transferred to over-ground walking. Therefore, this study supports the possibility of using a treadmill to, for instance, lengthen or quicken stepping movements or manage new constraints in individuals with obesity. Figure 3: Transfer Index for adults with normal weight (dark grey) and obesity (dark brown) for double-limb support time (DST) symmetry (**a**) and step length (SL) symmetry (**b**). The transfer index indicates the amount of adaptation transfer from the treadmill to over-ground walking in each BMI group. For both adapted parameters, the transfer index is greater in adults with normal weight than in adults with obesity. Error bars indicate the standard deviation. Asterisk indicates a significant difference between groups. * \(p<0.05\). Contrary to our hypothesis, however, we did not observe any differences in step length symmetry between normal-weight adults and adults with obesity throughout the testing conditions. One interpretation is that the amounts of adaptation, aftereffects, savings, and transfers for step length symmetry may depend on the imposed walking speed as a mediator of the effect of obesity on gait symmetry. In the current study, to maximize the effect of obesity on gait adaptation, treadmill belt speeds were set at each participant's preferred over-ground walking speed. Specifically, each participant's treadmill baseline walking speed was matched with their self-selected comfortable walking speed over the ground, which is more like everyday life where speed is sometimes imposed. However, we acknowledge that using a preferred speed for each participant may have limited the amount of variability in response to the split-belt perturbation. Given that each participant walked at a comfortable speed and adapted to the split-belt perturbation with a 2:1 speed ratio between the fast and slow belt, this explains how participants with obesity adapted and washed out at similar rates to participants with normal weight despite a slower walking speed. Future research may elucidate whether a fixed split-belt speed ratio may affect the rate of adaptation (split-belt) and de-adaptation (tied-belt) across BMI groups. Interestingly, the initial double-limb support times of both the slow (right) leg and the fast (left) leg over the gait cycle were larger in adults with obesity versus adults with normal weight over all of the testing conditions. This finding suggests that temporal gait is affected by obesity, which is consistent with previous findings [5; 6; 12]. Researchers suggest that prioritizing postural stability is likely primary for adults who have less ability to recover from a loss of balance [24].