Comparing the 30–15 intermittent fitness test and treadmill test on VO₂ max in elite female footballers

Purpose The study compared the 30–15 intermittent fitness test (30–15 IFT) and the treadmill-based multistage incremental test to evaluate their effectiveness in assessing cardiorespiratory fitness in elite female football players. Methods Fifteen Slovenian National A Team female football players (age = 24.4 ± 5.7 years; height = 166.5 ± 6.2 cm; weight = 59.9 ± 6.0 kg) completed the 30–15 IFT and treadmill tests on separate occasions. Maximal running speed (MRS), maximal oxygen consumption (VO₂max), and maximum heart rate (HRmax) were measured, with Pearson’s correlation coefficients used to assess their relationships. Results A moderate positive correlation was found between mean MRS treadmill speed (MRS_Treadmill) and VO₂max from the 30–15 IFT (r = 0.533, p = 0.041). The VO₂ max from the 30–15 IFT and treadmill test showed a strong correlation (r = 0.756, p = 0.002), while the correlation between treadmill VO₂max and mean MRS 30–15 IFT speed (MRS_30–15 IFT) was nearly perfect (r = 0.977, p = 0.000). The intraclass correlation coefficient (ICC ) for single VO₂max measurements was 0.689 [95% confidence interval (CI) = 0.271–0.888, p = 0.002], indicating moderate agreement, and 0.816 (95% CI: = 0.426 – 0.941, p = 0.002) for average measurements, indicating strong agreement. Conclusions These results are important for coaches of elite women’s football. The reduced variability suggests that cardiorespiratory fitness measures are more consistent in elite athletes than in diverse sports populations. This study’s unique contribution lies in its focus on elite national female football players, providing specific findings that enhance the utility of the 30–15 IFT in this specialised context.