Connecting the legs with a spring improves human running economy

Abstract

Spring-like tissues attached to the swinging legs of animals are thought to improve running economy by simply reducing the effort of leg swing. Here we show that a spring, or 'exotendon,' connecting the legs of a human runner improves economy instead through a more complex mechanism that produces savings during both swing and stance. The spring increases the energy optimal stride frequency; when runners adopt this new gait pattern, savings occur in both phases of gait. Remarkably, the simple device improves running economy by 6.4 ± 2.8%, comparable to savings achieved by motorized assistive robotics that directly target the costlier stance phase of gait. Our results highlight the importance of considering both the dynamics of the body and the adaptive strategies of the user when designing systems that couple human and machine.

The exoskeleton expansion: improving walking and running economy

“…Seventeen publications presented improved human walking and/or running economy using an exoskeleton versus without using a device during preferred levelground conditions: twelve exoskeletons improved walking economy [11][12][13][25][26][27][28][29][30][31][32][33], four improved running economy [14,15,17,18], and one improved both walking and running economy [16] versus using no device ( Fig. 2).…”

“…Embedding 'smart mechanics' into passive exoskeletons provides an alternative to fully powered designs Laboratory-based exoskeletons are moving into the realworld through the use of small, transportable energy supplies [59] and/or by harvesting mechanical energy to power the device [60]. Despite these improvements, another way to circumnavigate the burden of lugging around bulky energy sources is by developing passive exoskeletons [13,17,18,31]. Passive exoskeletons have been able to assist the user by storing and subsequently returning mechanical energy to the user without injecting net positive mechanical work.…”

“…Since then, researchers have also developed autonomous active [15,16] and passive [17,18] exoskeletons that improve human running economy (Fig. 1).…”

A hip–knee–ankle exoskeleton emulator for studying gait assistance

“…While most of these effective exoskeletons are tethered, some of them are mobile (Collins et al, 2015; Kim et al, 2019; Lee et al, 2018; Mooney et al, 2014; Seo et al, 2016). In addition to walking, some exoskeletons have assisted running (Lee et al, 2017b; Nasiri et al, 2018; Simpson et al, 2019; Witte et al, 2020) and load carriage (Ding et al, 2016; Lee et al, 2018; Mooney et al, 2014). While this progress hints at the potential of exoskeleton assistance, simulations suggest that even greater metabolic cost reductions may be possible with assistance strategies that have yet to be tested (Dembia et al, 2017; Uchida et al, 2016).…”

Improving the Human Machine

“…Not exactly a bioengineering marvel, but the elastic worked. A controlled study showed that it reduced energy consumption during running by 6% [1]. Several other research teams are working on similar devices-called exoskeletons-that can help improve walking and running efficiency.…”