Short-term exercise training improves diaphragm antioxidant capacity and endurance

These experiments tested the hypothesis that short-term endurance exercise training would rapidly improve (within 5 days) the diaphragm oxidative/anti oxidant capacity and protect the diaphragm against contraction-induced oxid ative stress. To test this postulate, male Sprague-Dawley rats (6 weeks old ) ran on a motorized treadmill for 5 consecutive days (40-60 min . day(-1)) at approximately 65% maximal oxygen uptake. Costal diaphragm strips were e xcised from both sedentary control (CON, n=14) and trained (TR, n = 13) ani mals 24 h after the last exercise session, for measurement of in vitro cont raction properties and selected biochemical parameters of oxidative/antioxi dant capacity. Training did not alter diaphragm force-frequency characteris tics over a full range of submaximal and maximal stimulation frequencies (P > 0.05). In contrast, training improved diaphragm resistance to fatigue as contraction forces were better-maintained by the diaphragms of the TR anim als during a submaximal 60-min fatigue protocol (P < 0.05). Following the f atigue protocol, diaphragm strips from the TR animals contained 30% lower c oncentrations of lipid hydroperoxides compared to CON (P < 0.05). Biochemic al analysis revealed that exercise training increased diaphragm oxidative a nd antioxidant capacity (citrate synthase activity +18%, catalase activity +24%, total superoxide dismutase activity +20%, glutathione concentration 10%) (P < 0.05). These data indicate that short-term exercise training can rapidly elevate oxidative capacity as well as enzymatic and non-enzymatic a ntioxidant defenses in the diaphragm. Furthermore, this up-regulation in an tioxidant defenses would be accompanied by a reduction in contraction-induc ed lipid peroxidation and an increased fatigue resistance.