“…Such planar covariation of the elevation angles held for various gaits, such as running (Hicheur et al, 2006; Ivanenko et al, 2007), curved walking (Courtine and Schieppati, 2004), backward walking (Grasso et al, 1998; Hicheur et al, 2006), walking on inclined surfaces (Noble and Prentice, 2008), walking with bent or erect posture (Grasso et al, 2000), stepping over an obstacle (Ivanenko et al, 2005b; Maclellan and McFadyen, 2010), walking with body weight unloading (Ivanenko et al, 2002), and walking on a slippery surface (Cappellini et al, 2010), which suggests an invariant characteristic in locomotion. In addition, this characteristic appeared in toddlers (Cheron et al, 2001; Ivanenko et al, 2004, 2005a; Dominici et al, 2007, 2010; Hallemans and Aerts, 2009; Cappellini et al, 2016); neonates (Dominici et al, 2011); gait disorders (Grasso et al, 2004; Laroche et al, 2007; Leurs et al, 2012; Martino et al, 2014; Cappellini et al, 2016; Ishikawa et al, 2017; Wallard et al, 2018); and also various animals (Catavitello et al, 2018), including cats (Poppele and Bosco, 2003), dogs (Catavitello et al, 2015), monkeys (Courtine et al, 2005; Ogihara et al, 2012), and birds (Ogihara et al, 2014). Investigating the coordination structures has provided useful insights for adaptation mechanisms in locomotion.…”