This study examined the effects of four high-intensity interval-training (HIT) sessions performed over 2 weeks on peak volume of oxygen uptake [Formula: see text] the first and second ventilatory thresholds (VT1, VT2) and peak power output (PPO) in highly trained cyclists. Fourteen highly trained male cyclists [Formula: see text] performed a ramped cycle test to determine [Formula: see text]VT1, VT2, and PPO. Subjects were divided equally into a HIT group and a control group. The HIT group performed four HIT sessions (20 × 60 s at PPO, 120 s recovery); the [Formula: see text] test was repeated < 1 wk after the HIT program. Control subjects maintained their regular training program and were reassessed under the same timeline. There was no change in [Formula: see text] for either group; however, the HIT group showed a significantly greater increase in VT1 (+22% vs. −3%), VT2 (+15% vs. −1%), and PPO (+4.3 vs. −4%) compared to controls (all P < .05). This study has demonstrated that HIT can improve VT1, VT2 and PPO, following only four HIT sessions in already highly trained cyclists. Key words: cycling, cyclists, heart rate, oxygen uptake, short-term training, ventilatory threshold