Treadmill vs. overground walking: different response to physical interaction

Abstract

Rehabilitation of human motor function is an issue of growing significance, and human-interactive robots offer promising potential to meet the need. For the lower extremity, however, robot-aided therapy has proven challenging. To inform effective approaches to robotic gait therapy, it is important to better understand unimpaired locomotor control: its sensitivity to different mechanical contexts and its response to perturbations. The present study evaluated the behavior of 14 healthy subjects who walked on a motorized treadmill and overground while wearing an exoskeletal ankle robot. Their response to a periodic series of ankle plantar flexion torque pulses, delivered at periods different from, but sufficiently close to, their preferred stride cadence, was assessed to determine whether gait entrainment occurred, how it differed across conditions, and if the adapted motor behavior persisted after perturbation. Certain aspects of locomotor control were exquisitely sensitive to walking context, while others were not. Gaits entrained more often and more rapidly during overground walking, yet, in all cases, entrained gaits synchronized the torque pulses with ankle push-off, where they provided assistance with propulsion. Furthermore, subjects entrained to perturbation periods that required an adaption toward slower cadence, even though the pulses acted to accelerate gait, indicating a neural adaptation of locomotor control. Lastly, during 15 post-perturbation strides, the entrained gait period was observed to persist more frequently during overground walking. This persistence was correlated with the number of strides walked at the entrained gait period (i.e., longer exposure), which also indicated a neural adaptation. We show that the response of human locomotion to physical interaction differs between treadmill and overground walking. Subjects entrained to a periodic series of ankle plantar flexion torque pulses that shifted their gait cadence, synchronizing ankle push-off with the pulses (so that they assisted propulsion) even when gait cadence slowed. Entrainment was faster overground and, on removal of torque pulses, the entrained gait period persisted more prominently overground, indicating a neural adaptation of locomotor control.

Pose estimates from online videos show that side-by-side walkers synchronize movement under naturalistic conditions

“…However, as with many movement science paradigms, it is not known if walker synchronization occurs in real world settings, outside of the laboratory. This is especially relevant for the walking studies in the laboratory: researchers have found a substantial difference in biomechanics between walking on the treadmill and walking on level ground [21,22]. The synchronization of pairs of walkers observed on treadmill might not generalize to real life settings.…”

Dynamics of corticospinal motor control during overground and treadmill walking in humans

“…Possibly, changes in the evoked TA response may be related to peripheral mechanisms involved in stride time or cadence, as these parameters were significantly different between treadmill and overground walking in the present study. This interpretation is supported by studies that showed biomechanical differences between overground and treadmill gait (Carpinella et al 2010; Chiu et al 2015; Dingwell et al 2001; Lee and Hidler 2008; Ochoa et al 2017). In line with this, these potential changes in evoked TA responses could be due to differences in background electrical activity of dorsal horn spinal neurons.…”

“…The vast majority of previous studies investigating gait-related cortical oscillations have been conducted on standard, motorized treadmills. Overground walking, however, has been shown to differ from treadmill walking dynamically and mechanically (Alton et al 1998; Arsenault et al 1986; Carpinella et al 2010; Chiu et al 2015; Dingwell et al 2001; Lee and Hidler 2008; Ochoa et al 2017; Riley et al 2007; White et al 1998). For example, treadmill walking has been found to reduce kinematic variability (Chiu et al 2015; Dingwell et al 2001), increase local dynamic stability (Dingwell et al 2001), affect inter-limb coordination (Carpinella et al 2010), modify lower limb muscle activation patterns, and joint moments and powers (Lee and Hidler 2008).…”

Synchronization of walking “in the wild”

“…However, previous studies have to examine walking pairs on a treadmill, which is set at a fixed walking speed (17). Furthermore, biomechanical studies have found that normal ground walking is different from treadmill walking (21,22). The manipulation of walking speed and the very fact of walking on the treadmill might impact the synchronization results and prevent generalization of previous findings.…”