OXYGEN COST OF TREADMILL RUNNING IN 24-MONTH-OLD FISCHER-344 RATS

The oxygen cost of treadmill running is well documented in young adult rats. However, to our knowledge there are no detailed reports concern ing the oxygen cost of treadmill running in senescent rats. Young adul t (4 months; N = 8) and senescent (24 months; N = 8) female Fischer-34 4 rats were tested for O2 cost of treadmill running. One-half of the a nimals tested in each age group had completed 10 wk of endurance train ing. Oxygen cost of treadmill running, using a flow-through system, wa s measured on a per minute basis from 7-10 min of each work bout and a veraged. Separate work bouts were performed at 0%, 5%, and 10% grade a t 15. 20, 25, and 30 m.min-1. Oxygen cost of treadmill running for tra ined rats for all speeds and grades were not significantly different ( P = 0.77) from untrained animals: thus, data were pooled for oxygen co st of running. Results revealed significantly lower (P < 0.05) VO2 (ex pressed as ml.kg-1. min-1) for senescent rats vs young adult rats rest and at all comparable treadmill grades and speeds except for 5% grade , 25 m.min-1 and 10% grade. 20 m.min-1. In addition, resting VO2 was s ignificantly lower (P < 0.05) in old rats when compared with young rat s. Thus, we conclude that the oxygen cost of treadmill running is lowe r for 24-month-old rats than in 4-month-old rats except at higher work levels.