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BACKGROUND; Authors have proposed the hypothesis that, the mechanism change may result in the mismatch between the energy production and energy consumption during the aerobic exercise, and pyruvate can be transformed into lactic acid, which may prevent the accumulation of pyruvate in cytoplasm and in the energy production of glycolysis so as to ensure the fast energy supply in zymolysis; the mechanism of this biochemical event may be the adjustment of energizing velocity via glycomechanism zymolysis.OBJECTIVE: To observe the effect of oxygen inhalation on metabolic transition, study the mechanism of metabolic transition under the lactate threshold intensity in human body and animal, and verify the result consistency between the two.DESIGN: Randomized control observation.SETTING: Department of Physical Education, Hebei Normal University; Department of Physical Education, Langfang Teachers College.PARTICIPANTS: A total of 24 male university students majoring physical education were adopted, weight (58±4) kg,height (175±6) cm, age (21 ±2) years. They were consisted of 12 Level B national athletes and12 common students.Additionally 30 SD male rats were used.METHODS: The experiment was carried out in the Laboratory of Physical and Physiological Function, Department of Physical Education in Hebei Normal University from April to June in 2006. Twenty-four students were recruited to exercise incrementally in ergometer; in addition, thirty SD rats were assigned to swim incrementally, 15 rats in each group. First, the intensities of metabolic transition were determined, then the exercise protocol was repeated on the conditions of inhaling and not inhaling oxygen. For student group, 50 W loading was incremented every 2 minutes, while the rats were added with 1% of their weights until unacceptable. Gradually incremented loading was used to transform the aerobic mechanism to anaerobic mechanism. The vein blood oxygen partial pressure, pyruvate and lactate contents were measured before and during the exercise (lactate threshold intensity) to evidence the reliability and validity of hypothesis.MAIN OUTCOME MEASURES: The vein blood oxygen partial pressure, pyruvate and lactate contents under lactate threshold intensity and oxygen inhaling supplementary.RESULTS: All 24 testees and 30 rats were involved in the result analysis. ①During the gradually incremented exercise,the lactic acid curve obtained at the end of 2-minute loading showed the difference of metabolic transition intensity and training level in accordance with individual lactic acid threshold, which was obviously lower in the trained exercisers.②Under the lactate threshold intensity, the blood lactate was not correlated to the oxygen partial pressure whether in human body or rats and whether inhaling oxygen or not [(3.61±0.56), (5.43±0.55) mmol/L; (4.46±0.86), (7.80±0.27) kPa,r =0.31, 0.31, P ＞ 0.05]; there was significant difference between the blood lactate and pyruvate contents [(1.04±0.16),(0.91±0.37) mmol/L, P ＜ 0.001]. The human body's saturation of blood oxygen was no less than 98% during the entire protocol. ③Under the repeated exercise and lactate threshold intensity, the pyruvate average value was (0.97±0.17),(1.04±0.16) mmol/L; (0.93±0.25), (0.91 ±0.37) mmol/L, respectively. There was no significant difference between the blood pyruvate before the exercise and under the lactate threshold intensity in both human body and animals (P ＞ 0.05).CONCLUSION: There is no hypoxia at the transition from aerobic to anaerobic metabolism. Oxygen inhaling supplementary has no influence on the mechanism transition; It is not easy for the pyruvate to pass the myocyte membrane, but the lactate can. The result demonstrates that the pyruvate can transform to lactate directly, which can also prevent the accumulation of pyruvate in kytoplasm.