High-intensity interval training (HIIT) in junior and adult soccer has been shown to improve oxygen uptake (VO₂) and enhance soccer performance. The main purpose of this study was to examine the short term effects of a 5-week HIIT vs. high-volume training (HVT) program in 14-year-old soccer players regarding the effects on VO₂max and 1,000-m time (T₁₀₀₀) and on sprinting and jumping performance. In a 5-week period, 19 male soccer players with a mean (SD) age of 13.5 ± 0.4 years performed HIIT at close to 90% of maximal heart rate. The HVT intensity was set at 60-75% of maximal heart rate. VO₂max increased significantly (7.0%) from pre to post in HIIT but not after HVT. T₁₀₀₀ decreased significantly after HIIT (-10 vs. ~-5 seconds in HVT). Sprint performance increased significantly in both groups from pre to posttesting without any changes in jumping performance.