This would explain why runners who train on shorter times achieve better results. Those who run for shorter periods are less likely to suffer consequences from air pollution that would hinder their training or slow them down during a race.

This would explain the opposite discrepancy. If runners who train on longer time periods can adjust more easily, then if anything they should perform better than runners who train on shorter time periods.

This is a reason runners who train on shorter periods achieve better results. Less time spent training means a lower risk of injury, which means a higher chance of training consistently.

This would explain why runners who train on shorter time periods achieve better results. Those who run 90 minutes a day are less likely to lose motivation, and thus more likely to maintain their training and perform to their abilities.

This would explain why runners who train for 90 minutes a day achieve better results. They do not deplete their energy reserves before race day, while those who train on longer time periods use some of those reserves in training.