Fig. 1

Exercise preconditioning protects against myocardial injury induced by exhaustive exercise at early and late phases. a Serum cTnI level changes in EP and EP-induced cardioprotection in the EE group compared with the C group were significantly different, *P < 0.05. The EEP + E group and LEP + E group compared with the EE group were significantly different, ^§ P < 0.05. b HBFP staining shows myocardial hypoxia-ischemia. Non-ischemic myocardial cells with stained cytoplasm in brown. Hypoxic-ischemic area is bright crimson. The EE group, EEP group, EEP + E group and LEP + E group present different degrees of myocardial hypoxia-ischemia. Group C and the LEP group without a significant hypoxic-ischemic region stained in brown. In the EE, EEP + E group and especially LEP + E group, crimson hypoxic-ischemic regions are significant. Original magnification ×400; bar 20 μm. c, d HBFP positively stained area and integral optical density (IOD) changes in EP and EP-induced cardioprotection. The EE group compared with C group. The difference was significant, *P < 0.05. The EEP + E and LEP + E groups compared with the EE group were significantly different, ^§ P < 0.05. C control, EE exhaustive exercise, EEP early exercise preconditioning, LEP late exercise preconditioning, EEP + E early exercise preconditioning plus exhaustive exercise, LEP + E late exercise preconditioning plus exhaustive exercise (color figure online)