This study evaluated novel submaximal indicators of cardio-respiratory fitness during high constant-load (HCL) exercise tests in response to detraining. A central variable was the slow component VO₂ (SC); SC is defined as the difference between end-exercise VO₂ and 3-min VO₂ (Gaesser et a1. ESSR, 1996). Terminal heart rate (HR) and blood lactate (HLa) were taken at the end of HCL tests. Ten sedentary males (18-30 yr) were screened and gave informed consent. Subjects completed a maximal and HCL exercise test for baseline assessment. The maximal test variables, VO₂ peak and lactate threshold (LT), were used to set loads for the HCL tests and the training protocol. Cycle ergometer training was done ~30 min/day, 5 days/week for 6 weeks at . 70(LT – VO₂ peak). Subjects were tested at week six of training and then detrained for two weeks. HCL tests were repeated at one and two weeks of detraining and an additional maximal test was performed after week two. Significant differences (p<0.001) were found in terminal heart rate following one and two weeks of detraining compared to post-training values, with increases of 6.20% and 5%, respectively. No significant changes occurred for SC and HLa. While terminal heart rate is known to exhibit a rapid time course change in detraining, SC and HLa need to be studied for a longer detraining period.