Trail Runners Cannot Reach (V) over dotO2max during a Maximal Incremental Downhill Test

Purpose The purpose of this study was twofold: (i) determine if well-trained athletes can achieve similar peak oxygen uptake ((V) over dotO(2peak)) in downhill running (DR) versus level running (LR) or uphill running (UR) and (ii) investigate if lower limb extensor muscle strength is related to the velocity at VO2peak ((V) over dotO(2peak)) in DR, LR, and UR. Methods Eight athletes ((V) over dotO(2max) = 68 +/- 2 mL.min(-1).kg(-1)) completed maximal incremental tests in LR, DR (-15% slope), and UR (+15% slope) on a treadmill (+1, +1.5, and +0.5 km.h(-1) every 2 min, respectively) while cardiorespiratory responses and spatiotemporal running parameters were continuously measured. They were also tested for maximal voluntary isometric strength of hip and knee extensors and plantar flexors. Results Oxygen uptake at maximal effort was approximately 16% to 18% lower in DR versus LR and UR (similar to 57 +/- 2 mL.min(-1).kg(-1), 68 +/- 2 mL.min(-1).kg(-1), and 70 +/- 3 mL.min(-1).kg(-1), respectively) despite much greater (V) over dotO(2peak) (22.7 +/- 0.6 km.h(-1) vs 18.7 +/- 0.5 km.h(-1) and 9.3 +/- 0.3 km.h(-1), respectively). At (V) over dotO(2peak), longer stride length and shorter contact time occurred in DR versus LR and UR (+12%, +119%, -38%, and -61%, respectively). Contrary to knee extensor and plantar flexor, hip extensor isometric strength correlated to (V) over dotO(2peak) in DR, LR, and UR (r = -0.86 to -0.96, P < 0.05). At similar (V) over dotO(2) higher heart rate and ventilation emerged in DR versus LR and UR, associated with a more superficial ventilation pattern. Conclusions This study demonstrates that well-trained endurance athletes, accustomed to DR, achieved lower (V) over dotO(2peak) despite higher (V) over dotO(2peak) during DR versus LR or UR maximal incremental tests. The specific heart rate and ventilation responses in DR might originate from altered running gait and increased lower-limb musculotendinous mechanical loading, furthering our understanding of the particular physiology of DR, ultimately contributing to optimize trail race running performance.