title: Slow VO2 off-kinetics in skeletal muscle is associated with fast PCr off-kinetics--and inversely.
abstract: The computer model of the bioenergetic system in skeletal muscle, developed previously, was used to study the effect of the characteristic decay time of the parallel activation of oxidative phosphorylation [τ(OFF)] during muscle recovery on the muscle oxygen consumption rate (Vo2) and phosphocreatine (PCr) work-to-rest transition (off)-kinetics and on the relationship between the Vo2 and PCr rest-to-work transition (on)- and off-kinetics in moderate and heavy exercise. An increase in τ(OFF) slows down the initial phase of the muscle Vo2 off-kinetics and accelerates the PCr off-kinetics. As a result, the relationship between the initial phase of the Vo2 off-kinetics (lasting approximately 3-60 s in computer simulations) and the PCr off-kinetics is inverse: the slower the former, the faster the latter. A faster initial phase of the Vo2 off-kinetics is associated with a slower late phase of the Vo2 off-kinetics, and as a result, the integral of Vo2 above baseline during recovery, representing the oxygen debt, is identical in all cases [values of τ(OFF)] for a given PCr decrease. Depending on τ(OFF), the muscle Vo2 on-kinetics was either equally fast or slower than the Vo2 off-kinetics in moderate exercise and always slower in heavy exercise. PCr on-kinetics was always faster than PCr off-kinetics. This study clearly demonstrates that τ(OFF) has a pronounced impact on the mutual relations between the muscle Vo2 and PCr on- and off-kinetics.
authors.affiliation: Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland.
authors.forename: Bernard
authors.initials: B
authors.lastname: Korzeniewski
authors.forename: Jerzy A
authors.initials: JA
authors.lastname: Zoladz
mesh_terms: D003198:Computer Simulation; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism*; D005082:Physical Exertion / Q000502:physiology*; D012146:Rest / Q000502:physiology
chemical_list: D010725:Phosphocreatine
keywords: Vo2 off-kinetics; Vo2 on-kinetics; computer model; parallel activation; skeletal muscle