Bipedal gait can be stabilized through mechanically-appropriate mediolateral foot placement, although this strategy is disrupted in a subset of neurologically injured individuals with balance deficits. The goal of the present work was to develop a device to influence mediolateral foot placement during treadmill walking. We created a novel force-field using a combination of passive elasticity and active control; wires in series with extension springs run parallel to the treadmill belts and can be rapidly repositioned to exert mediolateral forces on the legs of users. This mechanical structure creates a channel-like force landscape that resists displacements of each leg away from its prescribed mediolateral position, producing near-linear effective mediolateral stiffness. The depth of these force-field channels can be predictably controlled by manipulating extension spring initial tension. In human testing, we found that the force-field can effectively "get-out-of-the-way" when desired, closely following the mediolateral leg trajectory with a delay of approximately 110 ms. The force-field can also encourage users to adjust their mediolateral foot placement in order to walk with either narrower or wider steps, without interfering with forward gait progression. Future work will test whether this novel device can help retrain a stable gait pattern in clinical populations.

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Insects have the highest mass‐specific metabolic rates among animals due in part to their tracheal respiratory system. However, it has been hypothesized that larger/older insects may have greater oxygen delivery problems than smaller/younger insects because longer tracheae may be less efficient. This effect of size on oxygen delivery may be most dramatic during development or locomotion when oxygen demands are greatest. We tested this hypothesis by comparing the metabolic profile of the jumping muscle during development in the American locust (Schistocerca americana). Developing grasshoppers increase their body mass over 200 times from 1st instar juveniles to adults. To determine whether there is a developmental shift in the metabolic profile of the jumping muscle, we compared how enzymatic markers for aerobic (citrate synthase) and anaerobic metabolism (lactate dehydrogenase) varied in 2nd, 4th, and 6th instar as well as adult grasshoppers. Lactate dehydrogenase increased 2.8 fold with age from the 2nd instar to the adult. In contrast, citrate synthase decreased 1.9 fold with age from the 2nd instar to the adult. These findings support the hypothesis that the metabolic profile of S. americana jumping muscle gradually increases its reliance on anaerobic metabolism with development. Our research supports previous findings that larger/older grasshoppers produce more powerful jumps that result in greater lactic acid production than smaller/younger grasshoppers.