“…To overcome the limitations of the observational approach in animal locomotion, modeling approaches have attracted recent research attention ( Bertram and Gutmann, 2009 ; Alexander, 1988 ; Marques et al, 2014 ; Markowitz and Herr, 2016 ; Swanstrom et al, 2005 ; Aoi et al, 2017 ; Usherwood and Davies, 2017 ; Ambe et al, 2018 ; Fujiki et al, 2018 ; Aoi et al, 2019 ; Toeda et al, 2019 ). Because the essential contribution of the legs can be represented by springs, the spring-loaded inverted pendulum (SLIP) model was developed to investigate animal locomotion mechanism from a dynamic viewpoint, particularly for human running and walking ( Blickhan, 1989 ; McMahon and Cheng, 1990 ; Seyfarth et al, 2002 ; Geyer et al, 2005, 2006 ; Srinivasan and Holmes, 2008 ; Lipfert et al, 2012 ; Seethapathi and Srinivasan, 2019 ). The SLIP model has been improved for examining gait in quadrupeds ( Full and Koditschek, 1999 ; Blickhan and Full, 1993 ; Farley et al, 1993 ; Tanase et al, 2015 ) to clarify the common and unique principles between animal gaits.…”