Marathon performance and pacing in the Doha 2019 women’s IAAF World Championships: extreme heat, sub-optimal pacing and high failure rates

Purpose. The Doha 2019 women’s World Championship marathon took place in extreme hot (32ºC), humid conditions (74% relative humidity [RH]) culminating in unprecedented (41%) failure rates. We explored whether extreme heat, or sub-optimal pacing was responsible for diminished performance against a temperate ‘control’ (London 2017; 19ºC, 59% RH) and whether physical characteristics, (e.g., body surface area, estimated VO2max, habitual heat exposure) explained performance. Method. Five-kilometre (km) pace (km.h-1) data underwent repeated-measures analyses of hot (Doha, n=40) vs temperate pacing and performance (London, n=78); within and between marathon pacing (finisher quartiles normalised against personal best; n=10 per group), and within hot marathon finishers vs non-finishers (up to 10km; normalised data). Possible predictors (multiple regression) of hot marathon pacing were explored. Tests to 0.05 alpha level, partial eta squared (ηp2) indicates effect size Results: Mean±SD Doha (14.82±0.96km.h-1) pace was slower (London 15.74±0.96km.h-1; p=0.00; ηp2=.500). In hot conditions, athletes finishing in positions 1-10 (Group1) started more conservatively (93.7±2.1% of PB) than slower runners (Groups 3 & 4; 96.6±2.8% of PB; p<0.05, ηp2=.303). Groups were not different at 15-km and then slowed immediately (Groups 3&4) or after 20-km (Group 2). Finishers and non-finishers adopted similar pace up to 10-km (p>0.05, ηp2=.003). World ranking predicted (p=0.00; r2=0.248) average pace in Doha. Conclusion. Extreme hot conditions reduced performance. Top 10 athletes adopted a conservative initial pace whereas lower-placing athletes adopted a faster, aggressive start. Pacing alone does not explain high failure rates in non-finishers. Athletes competing in the heat should initially pace conservatively to optimise performance.