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Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11–15 year olds
Author(s) -
Breese Brynmor C.,
Saynor Zoe L.,
Barker Alan R.,
Armstrong Neil,
Williams Craig A.
Publication year - 2019
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/ep087979
Subject(s) - oxygenation , kinetics , cycling , skeletal muscle , chemistry , work rate , vastus lateralis muscle , oxygen , medicine , intensity (physics) , motor unit recruitment , zoology , endocrinology , cardiology , heart rate , biology , electromyography , physics , archaeology , organic chemistry , quantum mechanics , blood pressure , history , psychiatry
New FindingsWhat is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( V ̇ O 2 ) kinetics display linear, first‐order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non‐linear features of phase IIV ̇ O 2kinetics may be determined by alterations in the dynamic balance between microvascular O 2 delivery and utilization in 11–15 year olds. The recruitment of higher‐order (i.e. type II) muscle fibres during ‘work‐to‐work’ cycling might be responsible for modulatingV ̇ O 2kinetics with chronological age.Abstract This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7–15.7 years) the relationship between pulmonary oxygen uptake ( V ̇ O 2 ) and muscle deoxygenation kinetics during moderate‐ and very heavy‐intensity ‘step’ cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy‐intensity step cycling (i.e. M → VH). PulmonaryV ̇ O 2was measured breath‐by‐breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near‐infrared spectroscopy. There were no significant differences in the phase II time constant ( τ V ̇ O 2 p) between U → M and U → VH (23 ± 6 vs . 25 ± 7 s; P = 0.36); however, the τ V ̇ O 2 pwas slower during M → VH (42 ± 16 s) compared to other conditions ( P < 0.001). Quadriceps TOI decreased with a faster ( P < 0.01) mean response time (MRT; i.e. time delay + τ) during U → VH (14 ± 2 s) compared to U → M (22 ± 4 s) and M → VH (20 ± 6 s). The difference (Δ) between the τ V ̇ O 2 pand MRT‐TOI was greater during U → VH compared to U → M (12 ± 7 vs . 2 ± 7 s, P < 0.001) and during M → VH (23 ± 15 s) compared to other conditions ( P < 0.02), suggesting an increased proportional speeding of fractional O 2 extraction. The slowing of the τ V ̇ O 2 pduring M → VH relative to U → M and U → VH correlated positively with chronological age ( r = 0.68 and 0.57, respectively, P < 0.01). In youths, ‘work‐to‐work’ transitions slowed microvascular O 2 delivery‐to‐O 2 utilization with alterations in phase IIV ̇ O 2dynamics accentuated between the ages of 11 and 15 years.