D1.S3.2(5) Interchangeability of time vs distance trials vs 30-15 IFT in estimating maximal aerobic speed in academy soccer players

We aimed to investigate whether a 6 min distance trial (6minDT), 1800 m time trial (1800mTT) or the 30-15 Intermittent Fitness Test (30-15IFT) may be used interchangeably to estimate Maximal Aerobic Speed (MAS) in academy soccer players, competing in the Premier League U18 and National League Alliance Academy North, in England. Twenty-six (n = 26) male academy soccer players (age: 17.2 ± 0.6 [15.5 - 18.5] years; stature: 178.4 ± 5.1 [170.0 - 193.2] cm; body mass: 71.8 ± 7.7 [60.0 - 90.4] kg), completed a 30-15IFT on a 3G pitch, with MAS defined as 87% of test final stage velocity. Distance and time trials were then performed on a full-size outdoor 3G or Grass pitch in a counterbalanced order. Total Distance was measured via 10 Hz Global Positioning System units with MAS determined as distance divided by time to completion. All tests were performed on a MD+2 or MD+3, each separated by 1-2 weeks. Ethics clearance was received by the institutional research ethics sub-committee. Data analysis was performed in RStudio (Posit Software, PBC). The associations between MAS estimates were calculated using Pearson’s product-moment correlation coefficients and a robust repeated measures ANOVA was performed (robustlmm package) to estimate marginal mean differences between tests (emmeans package). Players achieved a MAS (mean ± SD) of 4.39 ± 0.24 [3.77 - 4.78] m·s-1 during the 6minDT, 4.49 ± 0.26 [4.01 - 4.85] m·s-1 during the 1800mTT, and 4.94 ± 0.22 [4.59 - 5.32] m·s-1 during the 30-15IFT. All associations between tests were observed to be positive. Associations between 1800mTT and 6minDT ranged from moderate to very large (r = 0.72; 95% confidence interval, 0.46 to 0.86). Further moderate to very large associations were observed between the 30-15IFT and time and distance trials (6minDT: r = 0.65; 0.35 to 0.83; 1800mTT: 0.66, 0.37 to 0.84). MAS estimated from the 30-15IFT was significantly higher than that estimated from both the distance-based trial (6minDT: 0.57, 0.50 to 0.65 m·s-1, p<0.0001) and time-trial (1800mTT: 0.45, 0.37 to 0.52 m·s-1, p <0.0001). Our distance-based trial resulted in a lower estimation of MAS compared to the time trial (-0.13, -0.21 to -0.05 m·s-1, p = 0.0002). In conclusion, our data suggest that whilst there are some associations between MAS estimated from the 6minDT, 1800mTT, and 30-15IFT, all three tests provide clearly different estimations of MAS.