title: Symmorphosis and skeletal muscle V̇O2 max : in vivo and in vitro measures reveal differing constraints in the exercise-trained and untrained human.
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 (V̇O2 max ) in humans is unclear. Therefore, in vitro skeletal muscle mitochondrial V̇O2 max (Mito V̇O2 max , mitochondrial respiration of fibres biopsied from vastus lateralis) was compared with in vivo skeletal muscle V̇O2 max during single leg knee extensor exercise (KE V̇O2 max , direct Fick by femoral arterial and venous blood samples and Doppler ultrasound blood flow measurements) and whole-body V̇O2 max during cycling (Body V̇O2 max , indirect calorimetry) in 10 endurance exercise-trained and 10 untrained young males. In untrained subjects, during KE exercise, maximal O2 supply (KE Q̇O2max ) exceeded (462 ± 37 ml kg(-1) min(-1) , P < 0.05) and KE V̇O2 max matched (340 ± 22 ml kg(-1) min(-1) , P > 0.05) Mito V̇O2 max (364 ± 16 ml kg(-1) min(-1) ). Conversely, in trained subjects, both KE Q̇O2max (557 ± 35 ml kg(-1) min(-1) ) and KE V̇O2 max (458 ± 24 ml kg(-1) min(-1) ) fell far short of Mito V̇O2 max (743 ± 35 ml kg(-1) min(-1) , P < 0.05). Although Mito V̇O2 max was related to KE V̇O2 max (r = 0.69, P < 0.05) and Body V̇O2 max (r = 0.91, P < 0.05) in untrained subjects, these variables were entirely unrelated in trained subjects. Therefore, in untrained subjects, V̇O2 max is limited by mitochondrial O2 demand, with evidence of adequate O2 supply, whereas, in trained subjects, an exercise training-induced mitochondrial reserve results in skeletal muscle V̇O2 max being markedly limited by O2 supply. Taken together, these in vivo and in vitro measures reveal clearly differing limitations and excesses at V̇O2 max in untrained and trained humans and challenge the concept of symmorphosis as it applies to O2 supply and demand in humans.
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Jayson R
authors.initials: JR
authors.lastname: Gifford
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Ryan S
authors.initials: RS
authors.lastname: Garten
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Ashley D
authors.initials: AD
authors.lastname: Nelson
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Joel D
authors.initials: JD
authors.lastname: Trinity
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Melissa A H
authors.initials: MA
authors.lastname: Witman
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Weavil
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Tyler
authors.initials: T
authors.lastname: Mangum
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Corey
authors.initials: C
authors.lastname: Hart
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Cory
authors.initials: C
authors.lastname: Etheredge
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, UT, USA.
authors.forename: Jake
authors.initials: J
authors.lastname: Jessop
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, UT, USA.
authors.forename: Amber
authors.initials: A
authors.lastname: Bledsoe
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, UT, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Morgan
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: D Walter
authors.initials: DW
authors.lastname: Wray
authors.affiliation: Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Rossman
authors.affiliation: Geriatric Research, Education, and Clinical Center, Salt Lake City VAMC, Salt Lake City, UT, USA.|Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT, USA.|Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D016022:Case-Control Studies; D015444:Exercise; D006801:Humans; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010101:Oxygen Consumption; D055815:Young Adult