A7 General Biomechanics

2005 Comparative Biochemistry and Physiology A  
The cost of running in animals can be increased by running them uphill, or by loading either their center of mass or limb segments. Past investigators have used these manipulations to infer the costs of specific components of the stride and to investigate alterations in the function of individual muscles. However, these studies have been conducted without knowledge of the energy use by individual muscles. Our measurements were intended to fill this gap in our knowledge. We combined measurements
more » ... of organismal energetics during running in guinea fowl Numida meleagris, with estimates of energy use by all the individual muscles based on measurements of blood flow. When the mass of the animals was increased by backpack loading, most of the increased energy use by the muscles was due to just four stance phase muscles. Loading the distal limb segments increased energy use by most of the swing phase muscles, and by one muscle group previously thought to be only used during stance phase. Running the birds uphill increased energy use by almost all the stance phase muscles, and, somewhat surprisingly, by some swing phase muscles. The increases were very non-uniform across the stance phase muscles. Overall, our data indicate that uphill running and weighting cause very specific alterations in the partitioning of energy use among the muscles. This information provides the basis for more targeted studies of muscle function under conditions of altered energetic demand. The muscle fibres in the trunk of teleosts are arranged in complex 3D patterns that are thought to allow uniform strain distributions. At two days of development, the angle between longitudinal direction of the muscle fibres and the longitudinal axis is still relatively small. At eight weeks, higher angles with the longitudinal axis occur and a well-developed pseudo-helical pattern is observed that resembles the patterns described for adult teleosts. We designed a quantitative biomechanical model that predicts the strain distribution from measured local muscle-fibre orientations and prescribed body curvature and muscle deformations. For the Abstracts / Comparative Biochemistry and Physiology Part A 141 (2005) S135 -S154 www.elsevier.com/locate/cbpa fast muscle-fibre mass, we demonstrate that at day two a fairly uniform muscle-fibre strain is possible during bending of the body due to the relatively limited variation in the muscle-fibre distance from the mid-sagittal plane. The computed variation in the strain increases sharply from day 2 to 3, but decreases steadily towards 8 weeks. The most uniform strain fields were computed for 8 weeks (the latest stage that was considered). The uniformity at 8 weeks results from the pseudo-helical fibre arrangement and an appropriate shear deformation of the trunk muscles. The developmental changes in muscle-fibre arrangement and associated strain distribution can be explained if the local mechanical conditions of the muscle fibres drive the fibre reorientation. The interaction of a muscle and associated tendon during dynamic activities such as locomotion is critical for both force production and economical movement. It is generally assumed that, under submaximal conditions, muscle activation patterns are optimised to achieve maximum efficiency of work. However, if we change the power output required by a muscle, are activation conditions adopted that achieve a near optimum efficiency or is the increased Abstracts / Comparative Biochemistry and Physiology Part A 141 (2005) S135 -S154 S136 Abstracts / Comparative Biochemistry and Physiology Part A 141 (2005) S135 -S154 S148
doi:10.1016/j.cbpb.2005.05.012 fatcat:wmy2fzhkpbddrnlfygnj65dim4