Abstract: Purpose: The paper is to explore the characteristics and regular patterns of dynamic changes of muscle oxygen content during high intensity interval training in swimmers and to analyze the correlation of blood lactic acid (LA), heart rate (HR), ratings of perceived exertion (RPE) before and after the training. Methods: Swimmers (n=15) from Shandong province were selected randomly for moderate intensity-intermittent mode-training. Each subject was instructed to step on cycle ergometer with all his effort for 30s, then a rest for 120s, and this behavior was repeated 3 times (3 repetitions=1 session, all together 2 sessions, the resting time between both sessions was 180-240s). Muscle oxygen parameters of vastus lateralis in subjects were continuously monitored; RPE and HR were collected at the end of each 30s cycling; 10μl blood sample from fingertip for LA testing was collected before and after the training. Results:(1) During each 30s cycling, the oxygenated haemoglobin content (CHbO₂) and oxygen saturation in local tissue (TOI) of vastus lateralis both decreased sharply, while the reduced hemoglobin (CHb) increased quickly; (2) For both sessions, the levels of LA, HR and RPE post-training were higher than those pre-training respectively (p＜0.01); (3) There were high correlations between LA, HR and RPE before and after training respectively (p＜0.01). Conclusion: (1) Near Infrared Spectroscopy could be used continuously and noninvasively in real time to monitor the dynamic changes of TOI, CHbO₂ and CHb of working muscles, which reflected the training effect during training session; (2) For the individual high intensity interval training, LA, HR and RPE are effective indicators for monitoring the training session.

Key words: High Intensity Interval Training, Near Infrared Spectroscopy, Oxygen Saturation, Blood Lactic Acid