AUTHOR=Beltrame Thomas , Hughson Richard L. 

TITLE=Mean Normalized Gain: A New Method for the Assessment of the Aerobic System Temporal Dynamics during Randomly Varying Exercise in Humans

JOURNAL=Frontiers in Physiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00504

DOI=10.3389/fphys.2017.00504

ISSN=1664-042X

ABSTRACT=<p>The temporal dynamics of the oxygen uptake (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula>) during moderate exercise has classically been related to physical fitness and a slower <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> dynamics was associated with deterioration of physical health. However, methods that better characterize the aerobic system temporal dynamics remain challenging. The purpose of this study was to develop a new method (named mean normalized gain, <italic>MNG</italic>) to systematically characterize the <inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> temporal dynamics. Eight healthy, young adults (28 ± 6 years old, 175 ± 7 cm and 79 ± 13 kg) performed multiple pseudorandom binary sequence cycling protocols on different days and time of the day. The <italic>MNG</italic> was calculated as the normalized amplitude of the <inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> signal in frequency-domain. The <italic>MNG</italic> was validated considering the time constant τ obtained from time-domain analysis as reference. The intra-subject consistency of the <italic>MNG</italic> was checked by testing the same participant on different days and times of the day. The <italic>MNG</italic> and τ were strongly negatively correlated (<italic>r</italic> = −0.86 and <italic>p</italic> = 0.005). The <italic>MNG</italic> measured on different days and periods of the day was similar between conditions. Calculations for the <italic>MNG</italic> have inherent filtering characteristics enhancing reliability for the evaluation of the aerobic system temporal dynamics. In conclusion, the present study successfully validated the use of the <italic>MNG</italic> for aerobic system analysis and as a potential complementary tool to assess changes in physical fitness.</p>