Haematological rather than skeletal muscle adaptations contribute to the increase in peak oxygen uptake induced by moderate endurance training.
It remains unclear whether improvements in peak oxygen uptake (V̇(O2peak)) following endurance training (ET) are primarily determined by central and/or peripheral adaptations. Herein, we tested the hypothesis that the improvement in V̇(O2peak) following 6 weeks of ET is mainly determined by haematological rather than skeletal muscle adaptations. Sixteen untrained healthy male volunteers (age = 25 ± 4 years, V̇(O2peak) = 3.5 ± 0.5 l min(-1)) underwent supervised ET (6 weeks, 3-4 sessions per week). V̇(O2peak), peak cardiac output (Q̇(peak)), haemoglobin mass (Hb(mass)) and blood volumes were assessed prior to and following ET. Skeletal muscle biopsies were analysed for mitochondrial volume density (Mito(VD)), capillarity, fibre types and respiratory capacity (OXPHOS). After the post-ET assessment, red blood cell volume (RBCV) was re-established at the pre-ET level by phlebotomy and V̇(O2peak) and Q̇(peak) were measured again. We speculated that the contribution of skeletal muscle adaptations to the ET-induced increase in V̇(O2peak) would be revealed when controlling for haematological adaptations. V̇(O2peak) and Q̇(peak) were increased (P < 0.05) following ET (9 ± 8 and 7 ± 6%, respectively) and decreased (P < 0.05) after phlebotomy (-7 ± 7 and -10 ± 7%). RBCV, plasma volume and Hb(mass) all increased (P < 0.05) after ET (8 ± 4, 4 ± 6 and 6 ± 5%). As for skeletal muscle adaptations, capillary-to-fibre ratio and total Mito(VD) increased (P < 0.05) following ET (18 ± 16 and 43 ± 30%), but OXPHOS remained unaltered. Through stepwise multiple regression analysis, Q̇(peak), RBCV and Hb(mass) were found to be independent predictors of V̇(O2peak). In conclusion, the improvement in V̇(O2peak) following 6 weeks of ET is primarily attributed to increases in Q̇(peak) and oxygen-carrying capacity of blood in untrained healthy young subjects.
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
David
D
Montero
Institute of Human Movement Sciences and Sport, ETH Zurich, Switzerland.
Adrian
A
Cathomen
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.|Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, NC, USA.
Robert A
RA
Jacobs
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Daniela
D
Flück
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Jeroen
J
de Leur
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Stefanie
S
Keiser
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Thomas
T
Bonne
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Niels
N
Kirk
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Anne-Kristine
AK
Lundby
Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.
Carsten
C
Lundby
D000222:Adaptation, Physiological; D000328:Adult; D001810:Blood Volume / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006454:Hemoglobins / Q000502:physiology*; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D008931:Mitochondria, Muscle / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance; D055815:Young Adult
D006454:Hemoglobins; D007770:L-Lactate Dehydrogenase; D006593:Hexokinase