Figure 3

Entrainment results. The median relative step frequency (\(f_{r}\), step frequency divided by preferred step frequency in Baseline 2; magenta) of all subjects who entrained (N) is plotted over each trial duration. Step frequency (in Hz) is shown for the average subject in parentheses. Twenty-five and 75% quartiles are used to indicate the distribution at every time point (grey shaded area). All trial conditions are shown, including: \({\Delta }f_{m} = - 6\%\) in (a) and (b); \({\Delta }f_{m} = 0\%\) in (c) and (d); \({\Delta }f_{m} = 6\%\) in (e) and (f); \(A_{m} = 10\% \;{\text{BW}}\) in (a), (c) and (e); \(A_{m} = 30\% \;{\text{BW}}\) in (b), (d) and (f). The oscillations began at \({\text{Time}} = 0\;{\text{s}}\) and ended at approximately \({\text{Time}} = 600\;{\text{s}}\). During \(0 \le {\text{Time}} \le 300\; {\text{s}}\), subjects responded freely to the force oscillations. During \(300 \le {\text{Time}} \le 600\;{\text{s}}\), subjects were directed to follow the cadence of the metronome at their predetermined baseline step frequency (“frequency clamping”) even as the oscillations continued at a different frequency. There was no metronome used in trials where \({\Delta }f_{m} = 0\%\), since frequencies were already matched. As a result, these experiments ended after around \({\text{Time}} = 300\;{\text{s}}\). Note, median data are only shown for individuals who entrained at least once throughout the trial. In the trial condition where \({\Delta }f_{m} = 6\%\) and \(A_{m} = 10\% \;{\text{BW}}\), individual subject data are shown instead since no entrainment occurred.