The effect of an alteration from regular endurance to interval (10-20-30) training on, maximum oxygen uptake (VO2–max), running economy, blood variables pH, lactate, bicarbonate, and performance of runners was examined. Eighteen moderately trained runners (2 females and 16 males; VO2-max: 4353±222) (means±SD) were divided into a high intensity training (10-20-30; 1 female and 12 males) and a control (CON; 2 females and 3 males) group. For an eight week intervention period the 10-20-30 replaced two normal training sessions with 10-20-30 training consisting of low, moderate and high speed running (>90 pct. of maximal speed) for 30, 20 and 10 s, respectively, in 2-3 5-min intervals interspersed by 2 min of recovery, reducing training volume while CON continued the normal training. After the intervention period VO2–max, blood variables, and performance (5000m) was not altered in 10-20-30 compared to CON. The present study shows that interval training with short 10-s near maximal bouts maintain performance and VO2–max despite a reduction in training volume.