Respiration Physiology 109 (1997) 149–154 Bioenergetic characteristics of the costal and crural diaphragm in mammals Kelly Hodge, Scott K. Powers *, Jeff Coombes, Louise Fletcher, Haydar A. Demirel, Stephen L. Dodd, Daniel Martin Department of Exercise and Sport Sciences and Physical Therapy , Uniersity of Florida, Gainesille, FL 32 611, USA Accepted 16 June 1997 Abstract These experiments compared oxidative and glycolytic enzyme activity in the costal and crural diaphragm in seven adult mammals (mouse, rat, rabbit, ferret, sheep, pig, cow) ranging in body mass from approximately 0.03 to 422 kg. Segments of the costal and crural diaphragm from the aforementioned species were homogenized to determine the activities of the glycolytic enzyme, lactate dehydrogenase (LDH), and the Krebs cycle enzyme, citrate synthase (CS). The results indicated that metabolic differences between the costal and crural diaphragm do not exist in all mammalian species. Specifically, CS activity differed (P 0.05) between the costal and crural diaphragm (costal approximately 36% greater than crural) in only two species (rat and rabbit). Further, the oxidative capacity of the costal and crural diaphragm was significantly correlated with both breathing frequency and resting metabolic rate (r =0.92–0.57; P 0.05) across the species investigated. In contrast, glycolytic capacity was not significantly correlated (P 0.05) with either breathing frequency or resting metabolic rate. © 1997 Elsevier Science B.V. Keywords: Enzyme, oxidative vs. glycolytic, diaphragm; Mammals, comparative (seven species); Muscle, diaphragm, enzyme activity diaphragm has been classically considered one muscle with a single functional entity. However, recent reports have provided new insights into diaphragmatic structure and function. The di- aphragm is now thought to function as two mus- cles that act differently on the rib cage. For example, DeTroyer et al. (1981, 1982) separately stimulated the costal and crural parts of the di- 1. Introduction The diaphragm is the principal muscle of inspi- ration and is considered the most important venti- latory muscle in mammals (Sieck, 1988). The *Corresponding author. Tel.: +1 352 3920316; fax: +1 352 3920316; e-mail: spowers@hhp.ufl.edu 0034-5687/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0034-5687(97)00051-0