MARSH, R.L.; ELLERBY, D.J.; HENRY, H.T.; Northeastern University, Boston, MA: Energetic costs of back and limb loading in guinea fowl.

Loading studies have played a role in inferring the importance of various mechanical functions during running. Data showing a 1:1 relationship between the percentage increase in body mass and the percentage increase in gross metabolic rate have been used to suggest that practically the entire metabolic cost of running is due to the cost of supporting body weight. However, such data are open to alternate interpretations because of lack of information on the mechanical role and energy use of individual muscles. Net metabolic rate above rest is probably the proper measure of the influence of weighting and data from the literature indicate large differences in the effects of loading on net metabolic rata among various studies. Recently, we collected data indicating that in running guinea fowl 74% of the energy is used by stance-phase muscles, and 26% is used by swing-phase muscles. We asked whether the effect of back loading on metabolic rate in these animals was consistent with this distribution of energy use. Additionally, we examined the energetic consequences of limb-loading. Increasing the body weight of guinea fowl by 20% lead to a mean increase in net metabolic rate over rest of 15%, which is almost exactly what would be expected if 74% of the energy is used during stance. Limb loading leads to a large increase in metabolic rate, which can be explained by the large increase in internal work required to move the limbs. Supported by NIH AR47337 to RLM.