AUTHOR=Held Steffen , Rappelt Ludwig , Giesen René , Wiedenmann Tim , Deutsch Jan-Philip , Wicker Pamela , Donath Lars 

TITLE=Increased oxygen uptake in well-trained runners during uphill high intensity running intervals: A randomized crossover testing

JOURNAL=Frontiers in Physiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2023.1117314

DOI=10.3389/fphys.2023.1117314

ISSN=1664-042X

ABSTRACT=<p>The time spent above 90% of maximal oxygen uptake (<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max) during high-intensity interval training (HIIT) sessions is intended to be maximized to improve <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max. Since uphill running serves as a promising means to increase metabolic cost, we compared even and moderately inclined running in terms of time ≥90% <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max and its corresponding physiological surrogates. Seventeen well-trained runners (8 females &amp; 9 males; 25.8 ± 6.8yrs; 1.75 ± 0.08m; 63.2 ± 8.4kg; <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max: 63.3 ± 4.2 ml/min/kg) randomly completed both a horizontal (1% incline) and uphill (8% incline) HIIT protocol (4-times 5min, with 90s rest). Mean oxygen uptake (<inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>mean), peak oxygen uptake (<inline-formula id="inf6"><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>peak), lactate, heart rate (HR), and perceived exertion (RPE) were measured. Uphill HIIT revealed higher (<italic>p</italic> ≤ 0.012; partial eta-squared (pes) ≥ 0.351) <inline-formula id="inf7"><mml:math id="m7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>mean (uphill: 3.3 ± 0.6 vs. horizontal: 3.2 ± 0.5 L/min; standardized mean difference (SMD) = 0.15), <inline-formula id="inf8"><mml:math id="m8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>peak (uphill: 4.0 ± 0.7 vs. horizontal: 3.8 ± 0.7 L/min; SMD = 0.19), and accumulated time ≥90% <inline-formula id="inf9"><mml:math id="m9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max (uphill: 9.1 ± 4.6 vs. horizontal: 6.4 ± 4.0 min; SMD = 0.62) compared to even HIIT. Lactate, HR, and RPE responses did not show mode*time rANOVA interaction effects (<italic>p</italic> ≥ 0.097; pes ≤0.14). Compared to horizontal HIIT, moderate uphill HIIT revealed higher fractions of <inline-formula id="inf10"><mml:math id="m10" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max at comparable perceived efforts, heartrate and lactate response. Therefore, moderate uphill HiiT notably increased time spent above 90% <inline-formula id="inf11"><mml:math id="m11" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2</sub>max.</p>