Wearable robots reveal true metabolic benefits in outdoor testing

Testing wearable robots for gait assistance in outdoor settings yields more representative data regarding their metabolic benefits, as opposed to treadmill testing, according to a recent study.

“In summary, we observed an increase in the absolute metabolic consumption during treadmill walking and found that absolute metabolic reduction due to robotic assistance on a treadmill is at most as large as during outside walking. Thus, the relative metabolic change (δE) during treadmill walking will be systematically lower than the true relative metabolic change that would be found during outside, overground walking,” the researchers said.

Eight healthy, unimpaired participants (mean age 25.8 years, 5 men) were enrolled and given the prototype of the Myosuit Beta, a wearable robot designed to assist users during the stance phase of walking. Metabolic benefits of the device were compared across three settings: outside overground walking, on a self-paced treadmill with a virtual reality display, and on a standard treadmill with fixed gait speed.

In its assistive mode, the wearable device yields pronounced metabolic benefits relative to when it is set on zero-force mode, which is programmed to not interfere with human movement. [Sci Rep 2021;11:14833]

Comparing across three testing settings, the δE measurement was –10.6 percent during outside overground walking, significantly higher than both the self-paced (δE , –6.9 percent; p=0.015) and fixed (δE, –6.2 percent; p=0.008) gait treadmill settings.

Notably, δE was also significantly less pronounced in the five men vs the three women participants (p=0.007).

Looking at each component of δE further underscored the value of outdoor testing. Both indoor settings showed generally greater metabolic consumption during both zero-force and assistive modes of the device. No sex differential pattern was reported for this effect.

In terms of gait characteristics, the wearable robot’s assistive mode facilitated in significantly shorter mean stride times vs zero-force (p<0.001). Mean stride times were also significantly shorter in both indoor settings (p<0.001 for both). Stride time variability also tended to be higher indoors.

“If this had been a typical treadmill-based laboratory study, we would have concluded that Myosuit assistance reduced the metabolic cost of uphill walking by around 6–7 percent compared to wearing the Myosuit in zero-force mode,” the researchers said.

“However, with this study’s additional outdoor setting, we observed a significantly larger metabolic cost reduction of about 10 percent during outside, overground walking with the Myosuit. As a result, there is a 4.1-percent difference between the relative metabolic reduction found in the self-paced indoor setting and the one observed in the outdoor setting,” they added.

Future studies should also consider the technical complexity of the indoor self-paced, adaptive treadmill test, which could interfere with participants’ typical gait patterns. Without conclusive evidence of such, the researchers suggest that it may be preferrable to opt for the simpler, fixed-gait treadmill test and a direct transition to outdoor testing.