Your key workouts — that is, your high-intensity workouts and your extra-long workouts — are the most important to your running performance, so those should almost always be runs.

你的关键训练单元，也就是你的高强度训练单元和长距离单元，是你跑步计划中最重要的部分，因此这些单元几乎需要用跑来完成。