The purpose of the present investigation was to study the effects of eight weeks of intensive training at the beginning of the athletic season on perceived exertion and on the ratio of blood lactate concentration to ratings of perceived exertion (HLa : RPE) in young runners. Eight high-level middle-distance runners performed two exhausting exercises on an indoor track before and after eight weeks of training. The first test was an incremental exercise to determine their maximal oxygen uptake (VO(2) max), the velocity associated with VO(2) max (vVO(2) max), the velocity of the lactate concentration threshold (vLT) and the velocity delta 50 (vDelta50 : the velocity halfway between vVO(2) max and vLT). The second test was a constant-load all-out run at vDelta50 to determine the time to exhaustion at this intensity (tlim vDelta50). There were five training sessions a week with interval training twice a week. After eight weeks of training, vVO(2) max, vLT and tlim vDelta50 were not significantly different. The athletes perceived exercise as being harder after training than before at a same given relative velocity in the incremental test. During the all-out run at vDelta50, they felt that, at the same given relative time, they could endure less after than before training. Moreover, the HLa : RPE ratio was significantly lower after intensive interval-training performed immediately after the holidays. Consequently, two interval-training sessions per week would induce an overreaching state that is not yet characterized by a decrease in performance and physiological values whereas perceived exertion (RPE, ETL) and especially the HLa : RPE ratio allows the detection of changes in young high-level middle-distance runners.