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Oxygen Consumption During Maximal Exercise in Fischer 344 x Brown Norway F1 Hybrid Rats

Department of Medicine, Division of Physiology, University of California, San Diego.

Address correspondence to Mark Olfert, PhD, Department of Medicine 0623A, University of California–San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0623. E-mail: molfert{at}ucsd.edu

We characterized O₂ consumption (_O2) during treadmill exercise in 12-, 24-, and 35-month-old Fischer 344 x Brown Norway F1 hybrid (F344BNF1) rats. When accounting for differences in body mass (M_b), _O2peak decreased by 10% and 33% in 24- and 35-month-old rats, respectively, compared with rats at 12 months (analysis of covariance, p <.01). O₂ cost per unit work at _O2peak (i.e., _O2peak/work) was greater in 35-month-old rats compared with 12- and 24-month-old rats (p <.001). During submaximal exercise, the O₂ cost was greater in 24- and 35-month-old than 12-month-old rats (p <.01). Analysis of covariance revealed similar patterns irrespective of differences in M_b or lean M_b as covariates. The underlying mechanism responsible for increasing O₂ consumption in aged F344BNF1 rats during exercise, although partly explained by mechanical inefficiencies of locomotion, still remains to be determined.

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