Blood volume expansion does not explain the increase in peak oxygen uptake induced by 10 weeks of endurance training

Abstract

Purpose The endurance training (ET)-induced increases in peak oxygen uptake (V O 2peak) and cardiac output (Q peak) during upright cycling are reversed to pre-ET levels after removing the training-induced increase in blood volume (BV). We hypothesised that ET-induced improvements in V O 2peak and Q peak are preserved following phlebotomy of the BV gained with ET during supine but not during upright cycling. Arteriovenous O 2 difference (a-vO 2 diff; V O 2 /Q), cardiac dimensions and muscle morphology were studied to assess their role for the V O 2peak improvement. Methods Twelve untrained subjects (V O 2peak : 44 ± 6 ml kg −1 min −1) completed 10 weeks of supervised ET (3 sessions/ week). Echocardiography, muscle biopsies, haemoglobin mass (Hb mass) and BV were assessed pre-and post-ET. V O 2peak and Q peak during upright and supine cycling were measured pre-ET, post-ET and immediately after Hb mass was reversed to the individual pre-ET level by phlebotomy. Results ET increased the Hb mass (3.3 ± 2.9%; P = 0.005), BV (3.7 ± 5.6%; P = 0.044) and V O 2peak during upright and supine cycling (11 ± 6% and 10 ± 8%, respectively; P ≤ 0.003). After phlebotomy, improvements in V O 2peak compared with pre-ET were preserved in both postures (11 ± 4% and 11 ± 9%; P ≤ 0.005), as was Q peak (9 ± 14% and 9 ± 10%; P ≤ 0.081). The increased Q peak and a-vO 2 diff accounted for 70% and 30% of the V O 2peak improvements, respectively. Markers of mitochondrial density (CS and COX-IV; P ≤ 0.007) and left ventricular mass (P = 0.027) increased. Conclusion The ET-induced increase in V O 2peak was preserved despite removing the increases in Hb mass and BV by phlebotomy, independent of posture. V O 2peak increased primarily through elevated Q peak but also through a widened a-vO 2 diff, potentially mediated by cardiac remodelling and mitochondrial biogenesis. Keywords Blood volume • Cardiac output • Echocardiography • Haemoglobin mass • Maximal oxygen uptake • Peripheral adaptations • Supine cycling Abbreviations a-vO 2 diff Arteriovenous oxygen difference BV Blood volume CO Carbon monoxide COX-IV Cytochrome c oxidase subunit 4 CS Citrate synthase EDV End-diastolic volume ESV End-systolic volume ET Endurance training HAD Hydroxyacyl-CoA dehydrogenase [Hb] Haemoglobin concentration Hb mass Haemoglobin mass HR Heart rate HR peak Peak heart rate [La] Blood lactate concentration LV Left ventricle MCHC Mean corpuscular haemoglobin concentration MTT Mean transit time PV Plasma volumė Q Cardiac outpuṫ Q peak Peak cardiac output Communicated by Peter Krustrup.

Effects of Including Sprints in One Weekly Low-Intensity Training Session During the Transition Period of Elite Cyclists

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Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

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Increased oxygen extraction and mitochondrial protein expression after small muscle mass endurance training

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