Endurance time ( 28 12 minutes without precooling or airflow ) increased by 30 23 minutes with airflow ( ~ 109 % ; 95 % confidence interval = 12 , 45 minutes ; P < .001 ) and by 16 15 minutes with precooling ( ~ 61 % ; 95 % confidence interval = 4 , 25 minutes ; P = .013 ) , but it was not further extended when the strategies were combined ( 29 21 minutes longer than control ) .