Gifford 2016 J Physiol

Gifford JR, Garten RS, Nelson AD, Trinity JD, Layec G, Witman MA, Weavil JC, Mangum T, Hart C, Etheredge C, Jessop J, Bledsoe A, Morgan DE, Wray DW, Richardson RS (2015) Symmorphosis and skeletal muscle VO2max: in vivo and in vitro measures reveal differing constraints in the exercise-trained and untrained human. J Physiol 594:1741-51.

» PMID: 26614395 Open Access

Gifford JR, Garten RS, Nelson AD, Trinity JD, Layec G, Witman MA, Weavil JC, Mangum T, Hart C, Etheredge C, Jessop J, Bledsoe A, Morgan DE, Wray DW, Richardson RS (2015) J Physiol

Abstract: The concept of symmorphosis postulates a matching of structural capacity to functional demand within a defined physiological system, regardless of endurance exercise training status. Whether this concept applies to oxygen (O₂) supply and demand during maximal skeletal muscle O₂ consumption (V_O2max) in humans is unclear. Therefore, in vitro skeletal muscle mitochondrial V_O2max (Mito V_O2max, mitochondrial respiration of fibers biopsied from vastus lateralis) was compared to in vivo skeletal muscle V_O2max during single leg knee extensor exercise (_KEV_O2max, direct Fick by femoral arterial and venous blood samples and Doppler ultrasound blood flow measurements) and whole-body V_O2max during cycling (_BodyV_O2max, indirect calorimetry) in 10 endurance-exercise trained and 10 untrained young males. In untrained subjects, during KE exercise, maximal O₂ supply (_KEQ_O2max) exceeded (462 ± 37 ml∙kg-1 ∙min-1, P<0.05) and _KEV_O2max matched (340 ± 22 ml∙kg-1 ∙min-1, P>0.05) Mito V_O2max (364 ± 16 ml∙kg-1 ∙min-1). Conversely, in trained subjects both _KEQ_O2max (557 ± 35 ml∙kg-1 ∙min-1) and _KEV_O2max (458 ± 24 ml∙kg-1 ∙min-1) fell far short of _MitoV_O2max (743 ± 35 ml∙kg-1 ∙min-1, P<0.05). While _MitoV_O2max was related to _KEV_O2max (r = 0.69, P<0.05) and _BodyV_O2max (r = 0.91, P<0.05) in the untrained subjects, these variables were entirely unrelated in the trained subjects. Therefore, in the untrained, V_O2max is limited by mitochondrial O₂ demand, with evidence of adequate O₂ supply, while in trained subjects an exercise training-induced mitochondrial reserve results in skeletal muscle V_O2max being markedly limited by O₂ supply. Together these in vivo and in vitro measures reveal clearly differing limitations and excesses at V_O2max in untrained and trained humans and challenge the concept of symmorphosis as it applies to O₂ supply and demand in humans. This article is protected by copyright. All rights reserved. • Keywords: BMI, VO2max

Selected quotations

• The unique combination of in vivo and in vitro measures utilized in the present study clarifies the determinants of ̇V_O2max and identifies two very different sources of limitation to ̇V_O2max in untrained and endurance exercise-trained individuals. Among untrained individuals, ̇V_O2max appears to be limited and therefore determined by mitochondrial O₂ demand, despite evidence of adequate O₂ supply. By contrast, among trained individuals, O₂ supply appears to limit ̇V_O2max, despite the presence of a large mitochondrial respiratory reserve capacity.

Labels: MiParea: Respiration, Exercise physiology;nutrition;life style 

Organism: Human  Tissue;cell: Skeletal muscle  Preparation: Permeabilized cells 

Regulation: Oxygen kinetics  Coupling state: OXPHOS  Pathway: N, NS 

BMI, VO2max, MitoFit2022Hypoxia