The sport performance of swimming athletes in three different levels including 5 national high-level swimming athletes, 5 ordinary swimming athletes and 5 college students was investigated by near-infrared spectroscopy (NIRS). Four parameters of muscle oxygenation and blood lactate (BLa) concentration were simultaneously monitored during incremental exercise on the ergometer. It was found that inflection points of muscle oxygenation and BLa concentration were consistent with the human sport capacity. Moreover, inflection points of muscle oxygenation occurred earlier than those of BLa concentration in ordinary athletes and college students. It implies monitoring changes of muscle oxygenation is superior to BLa measurement under this condition, since BLa test has an unavoidable time lag. Significant correlation (r² = 0.948; P<0.05) was observed between inflection points of muscle oxygenation difference and inflection points of BLa concentration on workload. This relationship suggests changes of muscle oxygenation detected by NIRS is beneficial to the evaluation of athletes’ physiologic function and training load. Considering that muscle oxygenation could be in-vivo and non-invasively measured by NIRS, it may be a better indicator of exercise intensity than BLa measurement in the near future.