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The oxygen cost of treadmill running is well documented in young adult rats. However, to our knowledge there are no detailed reports concerning the oxygen cost of treadmill running in senescent rats. Young adult (4 months; N = 8) and senescent (24 months; N = 8) female Fischer-344 rats were tested for O2 cost of treadmill running. One-half of the animals tested in each age group had completed 10 wk of endurance training. Oxygen cost of treadmill running, using a flow-through system, was measured on a per minute basis from 7-10 min of each work bout and averaged. Separate work bouts were performed at 0%, 5%, and 10% grade at 15, 20, 25, and 30 m.min-1. Oxygen cost of treadmill running for trained rats for all speeds and grades were not significantly different (P = 0.77) from untrained animals; thus, data were pooled for oxygen cost of running. Results revealed significantly lower (P < 0.05) VO2 (expressed 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 significantly lower (P < 0.05) in old rats when compared with young rats. Thus, we conclude that the oxygen cost of treadmill running is lower for 24-month-old rats than in 4-month-old rats except at higher work levels.

CRISWELL, D., S. POWERS, S. DODD, J. LAWLER, W. EDWARDS, K. RENSHLER, and S. GRINTON, High intensity training-induced changes in skeletal muscle antioxidant enzyme activity. Med. Sci. Sports Exerc., Vol. 25, No. 10, pp. 1135–1140, 1993. These experiments tested the hypothesis that high inten

Recent evidence demonstrates that endurance exercise training improves the oxidative capacity of the major mammalian inspiratory muscle (e.g., costal diaphragm). In contrast, no data exist concerning the effects of exercise training on abdominal expiratory muscles. We tested the hypothesis that 12 wk of endurance exercise training would significantly increase the activity of selected beta oxidation and Krebs cycle enzymes of abdominal expiratory muscles of the rat. To test this hypothesis two groups of female Sprague-Dawley rats were studied: group 1, continuous exercise training (n = 13); and group 2, sedentary control (n = 6). Exercise trained animals ran 5 d.wk-1 on a motorized treadmill for 45 min.d-1 at approximately 75-80% VO2max. When compared with controls, exercise training resulted in elevated (P less than 0.05) activities of 3-hydroxy-acyl-Co-A dehydrogenase (HADH) and citrate synthase (CS) in two abdominal expiratory muscles (rectus abdominus and external obliques). In contrast, training did not alter (P greater than 0.05) CS or HADH activity in the internal obliques/transversus abdominus muscles. In general, the training-induced increases in expiratory muscles CS activity were relatively small (approximately 10-13%) when compared with the training-induced increase in CS activity in the plantaris muscle (approximately 44%). These data demonstrate that continuous exercise training results in small but statistically significant improvements in the oxidative and beta oxidation capacities of expiratory muscles.