Meeting Abstract
The consequences of footfall phasing in terms of limb work has previously been considered for a range of walking quadrupedal species with models using highly idealized limb forces (Usherwood and Self Davies 2017; also SICB, 2017). In the current study, we extend previous methods to exploit empirical force profiles (see Granatosky, 2016), and relate limb work cost contours to observed phasings across a range of duty factors. We take advantage of measurements on 10 species observed locomoting upside-down, 8 of which are also measured walking upright. This inverted/upright comparison presents different mechanical loading demands, and so contrasting cost surfaces. While the phases used during inverted and upright gaits broadly match low limb work conditions (varying as a function of duty factor), pure work minimization alone is insufficient to account for the selected phases. Upright primates tend to adopt a diagonal footfall sequence, whereas a lateral sequence is usually – very marginally – better. Similarly, a diagonal sequence would be narrowly predicted for many inverted gaits; however, vampire and fruit bats adopt a lateral sequence at very high duty factors, populating a slightly less favourable (though still low-cost) region. The mechanical principles underlying the limb work cost surfaces are discussed, as are non-energetic constraints that may prohibit certain duty factor / limb phase combinations. Granatosky, M.C. (2016). A mechanical analysis of suspensory locomotion in primates and other mammals. PhD thesis, Duke University. Usherwood J.R. and Self Davies Z.T. (2017) Work minimization accounts for footfall phasing in slow quadrupedal gaits. eLife 2017;6:e29495 doi:10.7554/eLife.29495.
