Purpose: The purpose of this study was twofold: (i) determine if well-trained athletes can achieve similar peak oxygen uptake (V˙O_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 V˙O_2peak (vV˙O_2peak) in DR, LR, and UR. Methods: Eight athletes (V˙O_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 (~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 vV˙O_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 vV˙O_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 vV˙O_2peak in DR, LR, and UR (r = −0.86 to −0.96, P < 0.05). At similar V˙O₂, 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˙O_2peak despite higher vV˙O_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.

This study explores the cardiorespiratory and muscular fatigue responses to downhill (DR) vs uphill running (UR) at similar running speed or similar oxygen uptake (V̇O₂). Eight well-trained, male, trail runners completed a maximal level incremental test and three 15-min treadmill running trials at ±15% slope: i) DR at ~6 km·h⁻¹ and ~19% V̇O_2max (LDR); ii) UR at ~6 km·h⁻¹ and ~70% V̇O_2max (HUR); iii) DR at ~19 km·h⁻¹ and ~70% V̇O_2max (HDR). Cardiorespiratory responses and spatiotemporal gait parameters were measured continuously. Maximal isometric torque was assessed before and after each trial for hip and knee extensors and plantar flexor muscles. At similar speed (~6 km·h⁻¹), cardiorespiratory responses were attenuated in LDR vs HUR with altered running kinematics (all p < 0.05). At similar V̇O₂ (~3 l·min⁻¹), heart rate, pulmonary ventilation and breathing frequency were exacerbated in HDR vs HUR (p < 0.01), with reduced torque in knee (−15%) and hip (−11%) extensors and altered spatiotemporal gait parameters (all p < 0.01). Despite submaximal metabolic intensity (70% V̇O_2max), heart rate and respiratory frequency reached maximal values in HDR. These results further our understanding of the particular cardiorespiratory and muscular fatigue responses to DR and provide the bases for future DR training programs for trail runners.

Mountain running races are becoming increasingly popular, although our understanding of the particular physiology associated with downhill running (DR) in trained athletes remains scarce. This study explored the cardiorespiratory responses to high-slope constant velocity uphill running (UR) and DR. Eight endurance athletes performed a maximal incremental test and 2 15-min running bouts (UR, +15%, or DR, -15%) at the same running velocity (8.5 ± 0.4 km·h-1). Oxygen uptake ([Formula: see text]O2), heart rate (HR), and ventilation rates ([Formula: see text]E) were continuously recorded, and blood lactate (bLa) was measured before and after each trial. Downhill running induced a more superficial [Formula: see text]E pattern featuring reduced tidal volume (p < .05, ES = 6.05) but similar respiratory frequency (p > .05, ES = 0.68) despite lower [Formula: see text]E (p < .05, ES = 5.46), [Formula: see text]O2 (p < .05, ES = 12.68), HR (p < .05, ES = 6.42), and bLa (p < .05, ES = 1.70). A negative slow component was observed during DR for [Formula: see text]O2 (p < .05, ES = 1.72) and HR (p < .05, ES = 0.80). These results emphasize the cardiorespiratory responses to DR and highlight the need for cautious interpretation of [Formula: see text]O2, HR, and [Formula: see text]E patterns as markers of exercise intensity for training load prescription and management.

Purpose: This study aimed to determine the contribution of metabolic, cardiopulmonary, neuromuscular, and biomechanical factors to the energy cost (ECR) of graded running in well-trained runners. Methods: Eight men who were well-trained trail runners (age: 29 [10] y, mean [SD]; maximum oxygen consumption: 68.0 [6.4] mL·min⁻¹·kg⁻¹) completed maximal isometric evaluations of lower limb extensor muscles and 3 randomized trials on a treadmill to determine their metabolic and cardiovascular responses and running gait kinematics during downhill (DR: −15% slope), level (0%), and uphill running (UR: 15%) performed at similar O₂ uptake (approximately 60% maximum oxygen consumption). Results: Despite similar O₂ demand, ECR was lower in DR versus level running versus UR (2.5 [0.2] vs 3.6 [0.2] vs 7.9 [0.5] J·kg⁻¹·m⁻¹, respectively; all P < .001). Energy cost of running was correlated between DR and level running conditions only (r² = .63; P = .018). Importantly, while ECR was correlated with heart rate, cardiac output, and arteriovenous O₂ difference in UR (all r² > .50; P < .05), ECR was correlated with lower limb vertical stiffness, ground contact time, stride length, and step frequency in DR (all r² > .58; P < .05). Lower limb isometric extension torques were not related to ECR whatever the slope. Conclusion: The determining physiological factors of ECR might be slope specific, mainly metabolic and cardiovascular in UR versus mainly neuromuscular and mechanical in DR. This possible slope specificity of ECR during incline running opens the way for the implementation of differentiated physiological evaluations and training strategies to optimize performance in well-trained trail runners.

Il est bien établi chez les physiologistes, que si l’exercice de course en montée sollicite préférentiellement des contractions musculaires concentriques, l’exercice de course en descente requiert des actions musculaires frénatrices, majoritairement excentriques. L’exercice de course en descente à intensité sous-maximale génère un stimulus mécanique plus important pour un niveau de sollicitation métabolique moindre (i.e., V̇O2). Basée sur 3 études expérimentales, cette thèse de doctorat explore la physiologie spécifique de la course en déclivité, ainsi que ses prédicteurs physiologiques. Notre première étude montre une amplitude des réponses cardiorespiratoires amoindrie, une ventilation plus superficielle et une composante lente négative de consommation d’oxygène et de fréquence cardiaque en course en descente versus montée à vitesse constante et identique (8,5 km·h-1, pente de 15%). Lors de tests incrémentaux maximaux en course en descente vs montée vs plat, notre 2ème, partie A étude démontre que des coureurs bien entraînés, familiarisés avec la course en descente, peuvent atteindre FCmax, mais pas V̇O2max en descente. Lorsque les courses en descente et montée sont réalisées à même intensité métabolique (70% V̇O2max), notre 2ème (B) étude démontre que la course en descente (19 km·h-1, pente de -15%) induit des réponses cardiorespiratoires supérieures (FC et V̇E), une composante lente de V̇O2 significative et engendre une fatigue supérieure à la course en montée (6 km·h-1, pente de +15%). Enfin, une étude de terrain (étude 3) montre que les performances de 5 km de course en montée et en descente partagent quelques prédicteurs physiologiques communs (V̇O2max, force musculaire des membres inférieurs), bien que dans des proportions différentes. De plus, ces deux contre-la-montre sont également déterminés par des prédicteurs physiologiques spécifiques (i.e., raideur musculo-tendineuse en descente et indice de masse corporelle en montée). Nos résultats améliorent notre compréhension de la physiologie spécifique à la course en descente vs montée et ouvrent la voie des applications à l’entraînement des traileurs avec le but ultime d’optimiser leur performance.