Biewener, A. A. and McGowan, C. and Card, G. M. and Baudinette, R. V. (2004) Dynamics of leg muscle function in tammar wallabies (M. eugenii) during level versus incline hopping. Journal of Experimental Biology, 207 (2). pp. 211-223. ISSN 0022-0949 http://resolver.caltech.edu/CaltechAUTHORS:20110908-153457662
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The goal of our study was to examine whether the in vivo force-length behavior, work and elastic energy savings of distal muscle-tendon units in the legs of tammar wallabies (Macropus eugenii) change during level versus incline hopping. To address this question, we obtained measurements of muscle activation (via electromyography), fascicle strain (via sonomicrometry) and muscle-tendon force (via tendon buckles) from the lateral gastrocnemius (LG) and plantaris (PL) muscles of tammar wallabies trained to hop on a level and an inclined (10°, 17.4% grade) treadmill at two speeds (3.3 m s^(-1) and 4.2 m s^(-1)). Similar patterns of muscle activation, force and fascicle strain were observed under both level and incline conditions. This also corresponded to similar patterns of limb timing and movement (duty factor, limb contact time and hopping frequency). During both level and incline hopping, the LG and PL exhibited patterns of fascicle stretch and shortening that yielded low levels of net fascicle strain [LG: level, -1.0±4.6% (mean ± s.e.m.) vs incline, 0.6±4.5%; PL: level, 0.1±1.0% vs incline, 0.4±1.6%] and muscle work (LG: level, -8.4±8.4 J kg^(-1) muscle vs incline, -6.8±7.5 J kg^(-1) muscle; PL: level, -2.0±0.6 J kg^(-1) muscle vs incline, -1.4±0.7 J kg^(-1) muscle). Consequently, neither muscle significantly altered its contractile dynamics to do more work during incline hopping. Whereas electromyographic (EMG) phase, duration and intensity did not differ for the LG, the PL exhibited shorter but more intense periods of activation, together with reduced EMG phase (P<0.01), during incline versus level hopping. Our results indicate that design for spring-like tendon energy savings and economical muscle force generation is key for these two distal muscle-tendon units of the tammar wallaby, and the need to accommodate changes in work associated with level versus incline locomotion is achieved by more proximal muscles of the limb.
|Additional Information:||© 2004 The Company of Biologists. Accepted 24 October 2003. Published January 15, 2004. The authors are indebted to Jayne Skinner for her superb assistance in caring for and handling the animals during experiments. We thank members of our lab groups, as well as two referees, for helpful comments on earlier drafts of this manuscript and are most appreciative of the four tammar wallabies that performed so well for us in these experiments. This work was supported by NSF grant IBN-9306793 (to A.A.B.) and ARC grant –A19943044 (to R.V.B.).|
|Subject Keywords:||muscle–tendon unit, work, elastic energy, force–length, lateral gastrocnemius, plantaris, muscle, hopping, locomotion, tammar wallaby, Macropus eugenii|
|Official Citation:||A. A. Biewener, C. McGowan, G. M. Card and R. V. Baudinette Dynamics of leg muscle function in tammar wallabies (M. eugenii) during level versus incline hopping J Exp Biol 2004 207:211-223. doi:10.1242/jeb.00764|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||08 Sep 2011 23:09|
|Last Modified:||26 Dec 2012 13:40|
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