Ferley et al. 2013, uphill versus level-grade interval training

RCT in 32 well-trained distance runners (J Strength Cond Res) comparing uphill, level-grade and control interval training over six weeks. Both training groups improved time to exhaustion at the velocity associated with VO₂max, with level-grade work producing the larger gain in that specific test. Indicates uphill intervals are a useful complementary stimulus rather than a superior replacement for flat intervals.