This study was designed to test the reproducibility of muscle oxygenation by NIRS in children during exercise. Twelve healthy non-obese and non-trained children performed one maximal graded test, and four 6-min constant load cycle exercises. Deoxy-hemoglobin (Hb/Mb- H+) data were averaged every 1, 5, 10, 20 and 30s. Hb/Mb- H+ data averaged every 5, 10, 20 and 30s showed good reproducibility. When averaged every second, Hb/Mb-H+ values were reproducible after the first minute of exercise. Based on 1s averaged signal modeling, time period and t values for Hb/Mb-H+ were not reproducible but mean response time values showed an acceptable reproducibility.