ABSTRACT.Thirty‐six boys, aged 11‐13, were tested on a bicycle ergometer prior to and following a six week training program. The subjects were ranked according to their &OV0312;o2max, blocked into three fitness levels and then randomly assigned to one of the four treatment groups. The first group (T1) trained at a heart rate of 170‐180 beats/min; the second group (T2) at 150‐160 beats/min; the third group (T3at 130‐140 beats/min; and the fourth group (T4acted as a control. The training was conducted on a bicycle ergometer three times a week, 12 min per session. Following training, the heart rates decreased significantly (P < .05) in the three training groups and blood lactate concentration decreased significantly (P < .05) in the T1group (T3at 130‐140 beats/min; and the fourth group ing groups demonstrated significant (P < .01) increases in physical performance with training, while the &OV0312;o2max, blood lactate concentration and O2pulse increased significantly (P < .05) in the T1group only at maximal work load.