Does the length used in the 30-15 International Fitness Test (40- vs 28-m) influence the maximal running speed achieved by under-18 players from different sports?

The maximal running speed (MRS) achieved in the 30-15 International Fitness Test (30-15IFT) is widely used to prescribe high-intensity interval training (HIIT). The 30-15IFT can be performed in either 40- (30-15IFT-40) or 28-meters (30-15IFT-28) length. Objectives: The aim of this study was to evaluate the MRS achieved in the 30-15IFT-40 and the 30-15IFT-28. Methods: Fifty U-18 players from different sports (handball: n=19, soccer: n=19, tennis n=12) attended two testing sessions. Results: MRS did not differ between the 30-15IFT-40 and the 30-15IFT-28 in either handball or soccer players. However, tennis players showed significantly greater MRS values in the 30-15IFT-28 than in the 30-15IFT-40 (20.80±1.87 vs 20.05±2.09 km·h-1; p = 0.030; ES = 0.38). In addition, tennis player showed significant greater MRS in the 30-15IFT-28 (20.80±1.87 km·h-1) than both handball (18.58±1.13 km·h-1; p < 0.001; ES = 1.53) and soccer players (18.74±0.93 km·h-1; p = 0.001; ES = 1.47). Conclusions: The different MRS values in the 30-15IFT-40 and the 30-15IFT-28, entail significant practical implications for HIIT prescription in tennis players.