Live high train low (LHTL) is a well-known training model for preparation of competitions. In this study, the thiobarbituric acid reacting substances (TBARS) levels and superoxide dismutase (SOD) activity were determined in heart, lung and muscle tissues of rats. They were intermittently exposed to hypobaric pressure of 523 mmHg, corresponding to an altitude of 3,000 m, and they performed swim training at sea level. Two groups of male rats were trained to swim for thirty minutes a day and 4 days a week, lasting 9 weeks. Two groups were exposed to hypobaria for 120 min a day and 4 days a week for 9 weeks in pressure cabin. 

In heart tissue, TBARS levels of normobaric trained (NbT) group was higher (P < 0,05) than those of the normobaric sedentary (control) group. TBARS levels of hypobaric trained (HbT) group was higher than those of the control and hypobaric sedentary (Hb) groups (P < 0.001; P < 0.01, respectively). TBARS levels of lung tissue of HbT group was also higher than those of the same groups (control; P < 0.01, Hb; P < 0.05, respectively). In muscle tissue, TBARS levels of HbT group was higher than those of the sedentary groups (control; P < 0.001, Hb; P < 0.05, respectively). SOD activity of heart tissue of HbT group was higher (P < 0.001) than that of the other groups. In lung tissue, SOD activity of control group was lower than that of the other groups (HbT; P < 0.001, NbT; P < 0.01, Hb; P < 0.01, respectively). In muscle tissue, SOD activity of HbT group was higher (P < 0.01) than that of the control group. 

The results of this study suggest that intermittent hypobaric exposure may augment exercise-induced oxidative stress in heart, lung and muscle of trained rats.