# Effects of Obesity on Adaptation Transfer from Treadmill to Over-Ground Walking
## 2 Materials and Methods
### Experimental Protocol  
Spatiotemporal walking data were collected at the Motor Development Lab and the Human Adaptation Lab in Sargent College, Boston University, Boston, MA, from July 2019 through to November 2019. Walking adaptation was characterized using a 6.10 m long \(\times\) 0.89 m wide pressure-sensitive gait carpet (Protokinetics, LLC; Peekskill, NY, USA; 120 Hz sampling frequency) and a split-belt treadmill with two independent belts and full-length force plates (Bertec Corporation, Columbus, OH; 1000 Hz sampling frequency). As these data were collected as part of a larger study evaluating navicular drop, the participants walked barefoot with stick-on foot pads throughout the experiment. The experimental paradigm is shown in Figure 1. The walking task involved six conditions. In the first condition, participants walked on the carpet at their own pace for two minutes. Participants began the trials standing 2 m before the edge of the carpet and ended the trials 2 m after walking off the carpet. Trials began and ended the walking with verbal prompts from the experimenter (i.e., \"Go\" and \"Stop\"). After that, they turned around and walked again. The participants' comfortable over-ground walking speeds were calculated by the total step length divided by the total step time (m/s) in the first over-ground condition. This was used to set the preferred walking speed in the following treadmill conditions. The participants then moved to the treadmill and performed four treadmill walking conditions (Figure 1). As the treadmill speed was constant within each of the four treadmill walking conditions, the transition phases between tied-belt and split-belt were discarded for the analysis. All the participants reported that their dominant leg was the right leg. During treadmill walking conditions, participants were positioned in the middle of the treadmill with their dominant leg on the right-side belt (the slow belt was always on the dominant leg). Participants were instructed to refrain from looking down at the belts. The treadmill had rails on the front, left, and right sides to grab in case they lost balance, but participants were instructed not to grab the rails unless they felt unbalanced. Before testing, all participants walked on a treadmill at their comfortable walking speed until they felt comfortable with treadmill walking and ready for testing. Participants initially performed a tied-belt walking condition for five minutes. During the tied-belt condition, the treadmill belt speeds were set at each participant's preferred over-ground walking speed. Following this, the participants underwent a split-belt condition for 10 min. During the split-belt condition, the belt under the left leg moved at the participant's preferred speed while the belt under the right leg moved at a speed 50% slower than their preferred speed. As has been demonstrated previously [15; 17; 22], this split-belt perturbation typically causes spatial and temporal gait asymmetries (i.e., visible interlimb difference); however, with 10 min of practice with'split-bells', gait symmetry is typically restored and the asymmetric stepping goes away. Following this split-belt condition, the participants walked on tied-belt for 5 min to wash out the perturbation. At the beginning of the washout condition, the participants typically exhibit the opposite asymmetry in their gait (i.e., they walk with an inter-limb difference in the opposite direction). Thus, we assessed the storage and retention of the novel walking pattern in the washout condition. By the end of the washout condition, the participants returned to symmetrical walking on the tied-belt. Participants