The base of the design and construction of an adaptive light-weight climbing robot is an understanding of the adaptive nature of small mammals’ motion on sloped supports. In the present study, the locomotor generalist Rattus norvegicus (the rat) served as the main biological paragon. Experiments were performed under X-ray high-speed videography with synchronized substrate reaction force (SRF) measurements, to allow calculation of inverse dynamics. Statistical analyses were performed to examine the effects of different substrate orientations on the kinematic variables. We obtained SRFs, torque and power patterns in the extremities and trunk of rats moving on simulated arboreal substrates at different substrate orientations (0°, 30°, 60°). During locomotion on horizontal substrates, rats prefer symmetrical gaits and switch to synchronous gaits at 60° inclination. Surprisingly, horizontal locomotion and locomotion on moderately inclined substrates (30°) differ only in the power invested in locomotion. Our results suggest that the trunk seems to play a more important role during locomotion at steeper inclines where rats switch to the more quasi-static in-phase gait. We conclude that this may be an indication of a change from a grounded to a climbing gait. Via bionic transfer we derived main basic principles, which we applied to the design of the robot Rat-Nic.
Biologically inspired robots, biomechanics, inverse dynamics, rat locomotion
 Mämpel, J., Andrada, E., Witte, H., Trommer, C., Karguth, A., Fischer, M.S., Voigt, D. & Gorb, S., Inspirat – Towards a biologically inspired climbing robot for the inspection of linear structures. Proceedings of the Eleventh International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines. Advances in Mobile Robotics, pp. 206–213, 2008.
 Inspirat project, www.inspirat.de, resp. Witte H., Fischer M.S., Karguth A. & Mämpel J., A bschlussbericht des BMBF-Projektes Inspirat. Berichte aus der Biomechatronik, ed. H.Witte, Ilmenauer Universitätsverlag: Ilmenau, in press.
 Andrada, E., Mämpel, J., Schmidt, A., Fischer, M.S., Karguth, A. & Witte H., Biomechanical analyses of rat locomotion during walking and climbing as a base for the design and construction of climbing robots. Design & Nature V: Comparing Design in Nature With Science and Engineering, ed. C. A. Brebbia & A. Carpi, WIT press: Southampton, pp. 165–177, 2010.
 Fischer, M.S. & Lehmann R., Application of cineradiography for the metric and kinematic study of in-phase gaits during locomotion of the pika. Zoology, 101, pp. 12–37, 1998.
 Fischer, M.S., Schilling, N., Schmidt, M., Haarhaus, D. & Witte H., Basic limb kinematics of small therian mammals. Journal of Experimental Biology, 205, pp. 1315–1338, 2002.
 Hackert, R., Schilling, N. & Fischer, M.S., Mechanical self-stabilization, a working hypothesis for the study of evolution of body proportions in terrestrial mammals? Comptes Rendus Paleovol, 5, pp. 541–549, 2006. doi: http://dx.doi.org/10.1016/j.crpv.2005.10.010
 Eaton, M.D., Evans, D.L., Hodgson, D.R. & Rose, R.J., Effect of treadmill incline and speed on metabolic rate during exercise in Thoroughbred horses. Journal of Applied Physiology, 79, pp. 951–957, 1995.
 Farley, C.T. & Emshwiller, M., Effi ciency of uphill locomotion in nocturnal and diurnal lizards. Journal of Experimental Biology, 199, pp. 587–592, 1996.
 Hanna, J.B., Schmitt, D. & Griffi n, T.M., The energetic cost of climbing in primates. Science, 320(5288), p. 898, 2008. doi: http://dx.doi.org/10.1126/science.1155504
 Cavagna, G.A., Heglund, N.C. & Taylor, C.R., Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure. American Journal of Physiology, 233, pp. 243–261, 1977a.
 Cavagna, G.A., Heglund, N.C. & Taylor, C.R., Walking, running and galloping: mechanical similarities between different animals. Scale Effects in Locomotion, ed. T.J. Pedley, Academic Press: London, pp. 111–125, 1977b.
 Kram, R. & Taylor, C.R., Energetics of running: a new perspective. Nature, 346, pp. 265–267, 1990. doi: http://dx.doi.org/10.1038/346265a0
 Demes, B., Larson, S.G., Stern, J.T., Jr., Jungers, W.L., Biknevicius, A.R. & Schmitt, D., The kinematics of primate quadrupedalism: hindlimb drive reconsidered. Journal of Human Evolution, 26(5-6), pp. 353–374, 1994. doi: http://dx.doi.org/10.1006/jhev.1994.1023
 Hirasaki, E., Kumakura, H. & Matano, S., Biomechanical analysis of vertical climbing in the spider monkey and the Japanese macaque. American Journal of Physical Anthropology, 113, pp. 455–472, 2000. doi: http://dx.doi.org/10.1002/1096-8644(200012)113:4<455::AID-AJPA2>
 Witte, H., Biltzinger, J., Hackert, R., Schilling, N., Schmidt, M., Reich, C. & Fischer, M.S., Torque patterns of the limbs of small therian mammals during locomotion on fl at ground. Journal of Experimental Biology, 205, pp. 1339–1353, 2002.
 Nyakatura, J.A., Andrada, E., Grimm, N., Weise, H. & Fischer, M.S., Kinematics and center of mass mechanics during terrestrial locomotion in Northern Lapwings (Vanellus vanellus, Charadriiformes). Journal Experimental Zoology A Ecological Genetics and Physiology, 317, pp. 580–594, 2012.
 Winter, D.A., Biomechanics and Motor Control of Human Movement, John Wiley & Sons: New York, 1990.
 Ogihara, N. Personal communication, 2010. Department of Mechanical Engineering, Keio University, Yokohama, Japan.
 Hunt, K.D., Cant, J.G.H., Gebo, D. L., Rose, M.D., Walker, S.E. & Youlatus D., Standardized descriptions of primate locomotor and postural modes. Primates, 37(4), pp. 363–387, 1996. doi: http://dx.doi.org/10.1007/BF02381373
 Schilling, N. & Hackert, R., Sagittal spine movements of small therian mammals during asymmetrical gaits. Journal of Experimental Biology, 209, pp. 3925–3939, 2006. doi: http://dx.doi.org/
 Schmitt, D., Forelimb mechanics as a function of substrate type during quadrupedalism in two anthropoid primates. Journal of Human Evolution, 26, pp. 441–457, 1994. doi: http://dx.doi. org/10.1006/jhev.1994.1027
 Lammers, A.R. & Biknevicius, A.R., The biodynamics of arboreal locomotion: the effects of substrate diameter on locomotor kinetics in the gray shorttailed opossum (Monodelphis domestica). Journal of Experimental Biology, 207, pp. 4325–4336, 2004. doi: http://dx.doi.org/
 Clarke, K.A., Differential fore-and hindpaw force transmission in the walking rat. Physiology & Behavior, 58, pp. 415–419, 1995. doi: http://dx.doi.org/10.1016/0031-9384(95)00072-Q
 Clarke, K.A., Smart, L. & Still, J., Ground reaction force and spatiotemporal measurements of the gait of the mouse. Behavior Research Methods, Instruments & Computers, 33(3), pp. 422–426, 2001. doi: http://dx.doi.org/10.3758/BF03195396
 Schmidt, A. & Fischer, M.S., Arboreal locomotion in rats – the challenge of maintaining stability. Journal of Experimental Biology, 213, pp. 3615–3624, 2010. doi: http://dx.doi.org/
 Andrada, E., Nyakatura, J.A., Müller, R., Rode, C. & Blickhan, R., Grounded running: An overlooked strategy for robots. Autonomous Mobile Systems 2012, Springer: Berlin Heidelberg, pp. 79–87, 2012. doi: http://dx.doi.org/10.1007/978-3-642-32217-4_9
 Preuschoft, H., Mechanisms for the acquisition of habitual bipedality: are there biomechanical reasons for the acquisition of upright bipedal posture? Journal of Anatomy, 204(5), pp. 363–384, 2004. doi: http://dx.doi.org/10.1111/j.0021-8782.2004.00303.x
 Preuschoft, H., Witte, H. & Fischer, M.S., Locomotion in nocturnal prosimians. Creatures of the Dark: The Nocturnal Prosimians, eds. L. Alterman et al., Plenum Press: New York, pp. 453–472, 1995. doi: http://dx.doi.org/10.1007/978-1-4757-2405-9_27
 Nyakatura, J.A. & Andrada, E., A mechanical link model of two-toed sloths: no pendular mechanics during suspensory locomotion. Acta Theriologica, 58(1), pp. 83–93, 2013. doi: http:// dx.doi.org/10.1007/s13364-012-0099-4
 Cohen, A.H. & Gans, C., Muscle activity in rat locomotion: movement analysis and electromyography of the fl exors and extensors of the elbow. Journal of Morphology, 146, pp. 177–196, 1975. doi: http://dx.doi.org/10.1002/jmor.1051460202
 Jenkins, P.A. & Weijs, W.A., The functional anatomy of the shoulder in the Virginia opossum (Didelphis virginiana). Journal of Zoology, 188, pp. 379–410, 1979. doi: http://dx.doi.org/
 Fowler, E.G., Gregor, R.J., Hodgson, J.A. & Roy, R.R., Relationship between ankle muscle and joint kinetics during the stance phase of locomotion in the cat. Journal of Biomechanics, 26, pp. 465–483, 1993. doi: http://dx.doi.org/10.1016/0021-9290(93)90010-C
 Dogan, S., Manley, P.A., Vanderby, R., Kohles, S.S., Hartman, L.M. & BcBeath, A.A., Canine intersegmental hip joint forces and moments before and after cemented total hip replacement. Journal of Biomechanics, 28, pp. 753–758, 1991.
 Lee, D.V., McGuigan, M.P., Yoo, E.H. & Biewener, A.A., Compliance, actuation, and work characteristics of the goat foreleg and hindleg during level, uphill, and downhill running. Journal of Applied Physiology, 104, pp. 130–141, 2008. doi: http://dx.doi.org/10.1152/japplphysiol. 01090.2006
 Blickhan, R., The spring-mass model for running and hopping. Journal of Biomechanics, 22, pp 1217–1227, 1989. doi: http://dx.doi.org/10.1016/0021-9290(89)90224-8
 Alexander, R.McN., Why mammals gallop? American Zoologist, 28, pp. 237–245, 2008.