PT  - JOURNAL ARTICLE
AU  - Cole S. Simpson
AU  - Cara G. Welker
AU  - Scott D. Uhlrich
AU  - Sean M. Sketch
AU  - Rachel W. Jackson
AU  - Scott L. Delp
AU  - Steve H. Collins
AU  - Jessica C. Selinger
AU  - Elliot W. Hawkes
TI  - Connecting the legs with a spring improves human running economy
AID  - 10.1101/474650
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 474650
4099  - http://biorxiv.org/content/early/2018/11/30/474650.short
4100  - http://biorxiv.org/content/early/2018/11/30/474650.full
AB  - 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.