On a bright morning this month, Yuliya Stepanova, one of Russia’s premier middle-distance runners over the last decade, churned through an interval session — six times 800 meters at a sub-three-minute pace, followed by six times 100 meters at a near sprint. She was paced by her husband, Vitaly Stepanov, a good runner who has completed a marathon in under three hours but by no means an elite athlete. Between the fifth and sixth repeats, as they jogged for 200 meters, Vitaly staggered but Yuliya moved in a tight, economical recovery stride, her face impassive, her blond ponytail dancing with each step.