Meeting Abstract

42.2  Jan. 6  The versatile mechanical function of two proximal hindlimb muscles in running turkeys ROBERTS, T.J.*; HIGGINSON, B.K.; Brown University, Providence, RI; Oregon State University, Corvallis Thomas_Roberts@Brown.edu

The muscles that power running must be remarkably flexible in their mechanical function. For example, the muscular system performs almost no net mechanical work during level running, but it must perform net positive work to produce mechanical energy during uphill running and net negative work to absorb mechanical energy during downhill running. We used sonomicrometry and EMG to test the hypothesis that the strain pattern in active muscles reflects the demand for mechanical work. Wild turkeys ran on a treadmill inclined to +6� or +12�, and declined to -6� and -12�. Muscle length and activity were measured in the femorotibialis muscle (FT), a knee extensor, and the caudal head of iliotibialis lateralis (ILPO), a knee and hip extensor. Both muscles were active during stance, and underwent cyclic stretch-shorten cycles. The amount of muscle shortening and lengthening during stance changed in demand for mechanical work at different treadmill inclines. Shortening strain increased with increases in running slope, from 0.078 � 0.035 at -12� to 0.30 � 0.038 at +12� for the ILPO, and lengthening strain decreased with running slope, from 0.156 � 0.032 at -12� to 0.042�.025 at +12� for the ILPO. In contrast to the significant variation in strain with running incline, there was little change in strain of the ILPO or FT across the range of running speeds studied. Unlike changes in running slope, increases in running speed are not associated with a change in the demand for net mechanical work. Thus, the observed pattern of muscle strain with slope and speed in these muscles is consistent with the hypothesis that muscle length changes during running are modulated in response to the demand for mechanical work. Supported by NIH grant AR46499.