Superoxide anion can be generated through a way of electron leak of respiratory chain and the reactive oxygen species (ROS) can be formed in the further reactions of O 2 · in mitochondria.

The mitochondrial respiratory chain not only produced ATP by proton ATPase utilizing proton motive force (ΔμH +) created through the coupling of electron transfer with proton translocation across inner mitochondrial membrane but also generated 95% of O - ·2 of the living body through the reaction of so called“electron leak”pathway.

Using an animal model of exercise induced fatigue by incremental exercise to exhaustion on a motor driven treadmill, the changes of the mitochondrial proton leak and electron leak in mitochondria of skeletal muscle from rats immediately after exhaustive exercise were observed.