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Open Access 01-05-2020 | Echocardiography | Original Article
Blood volume expansion does not explain the increase in peak oxygen uptake induced by 10 weeks of endurance training
Published in: European Journal of Applied Physiology | Issue 5/2020
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Purpose
The endurance training (ET)-induced increases in peak oxygen uptake (\(\dot{V}\)O2peak) and cardiac output (\(\dot{Q}\)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 \(\dot{V}\)O2peak and \(\dot{Q}\)peak are preserved following phlebotomy of the BV gained with ET during supine but not during upright cycling. Arteriovenous O2 difference (a-\(\bar{\text{v}}\)O2diff; \(\dot{V}\)O2/\(\dot{Q}\)), cardiac dimensions and muscle morphology were studied to assess their role for the \(\dot{V}\)O2peak improvement.
Methods
Twelve untrained subjects (\(\dot{V}\)O2peak: 44 ± 6 ml kg−1 min−1) completed 10 weeks of supervised ET (3 sessions/week). Echocardiography, muscle biopsies, haemoglobin mass (Hbmass) and BV were assessed pre- and post-ET. \(\dot{V}\)O2peak and \(\dot{Q}\)peak during upright and supine cycling were measured pre-ET, post-ET and immediately after Hbmass was reversed to the individual pre-ET level by phlebotomy.
Results
ET increased the Hbmass (3.3 ± 2.9%; P = 0.005), BV (3.7 ± 5.6%; P = 0.044) and \(\dot{V}\)O2peak during upright and supine cycling (11 ± 6% and 10 ± 8%, respectively; P ≤ 0.003). After phlebotomy, improvements in \(\dot{V}\)O2peak compared with pre-ET were preserved in both postures (11 ± 4% and 11 ± 9%; P ≤ 0.005), as was \(\dot{Q}\)peak (9 ± 14% and 9 ± 10%; P ≤ 0.081). The increased \(\dot{Q}\)peak and a-\(\bar{\text{v}}\)O2diff accounted for 70% and 30% of the \(\dot{V}\)O2peak 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 \(\dot{V}\)O2peak was preserved despite removing the increases in Hbmass and BV by phlebotomy, independent of posture. \(\dot{V}\)O2peak increased primarily through elevated \(\dot{Q}\)peak but also through a widened a-\(\bar{\text{v}}\)O2diff, potentially mediated by cardiac remodelling and mitochondrial biogenesis.