Progressive metabolite changes in individual human muscle fibers with increasing work rates

Abstract

Muscle biopsies were obtained from vastus lateralis muscles of four volunteers exercising at increasing work rates on a bicycle ergometer. Samples were taken at rest (t1), after a work load 23% below the blood lactate threshold (t2), 23% above this threshold (t3), and at exhaustion (t4). Individual muscle fibers were typed by their lactate dehydrogenase and adenylokinase levels and assayed for lactate, glucose-6-phosphate, and malate, (which preliminary data indicated to be the most responsive to increased activity) as well as ATP and phosphocreatine. The results in three of the four cases indicated that by the time of the t2 sample, almost all fibers, regardless of type, had been recruited. Additionally, there were no major differences in lactate concentration between type 1 and 2 fibers from muscle samples taken at t1, t2, and t3. It is concluded that in a muscle with fast-twitch glycolytic and slow-twitch oxidative fibers, all fibers share in the contraction to a substantial degree, even at moderate work loads, and that both the type 1 and 2 fibers contribute significantly to the initial rise in blood lactate during a graded exercise task. Metabolite responses in type 2 fibers differed in certain respects among the four participants. This is attributed to differences in their training backgrounds and consequent differences in type 2 fiber oxidative enzyme levels.

Energy metabolism in human slow and fast twitch fibres during prolonged cycle exercise.

“…To our knowledge, time-dependent changes in lactate in fibre-specific types have not been examined using a similar protocol to that employed in this study. In two studies employing cycling exercise with progressive increases in power output, no difference was observed in lactate concentration between the two major fibre types (Jacobs & Kaiser, 1982;Ivy, Chi, Hintz, Sherman, Hellendall & Lowry, 1987).…”

Effects of Reactive Oxygen Species on Aspects of Excitation‐Contraction Coupling in Chemically Skinned Rabbit Diaphragm Muscle Fibres

“…Although the overriding evidence suggests that ATP supply is not a limiting factor in skeletal muscle fatigue (Ivy et al 1987), myoplasmic [ATP] does fall by around 30 %. Xanthine is an intermediate product in purine nucleotide catabolism (degradation of adenosine to uric acid), and accumulation occurs in fatigued muscle (Sahlin et al 1991).…”

The Molecular Bases of Training Adaptation

“…Strong evidence also exists for the relationship between metabolite concentrations and contractile intensity and duration during both continuous and intermittent models of electrical stimulation and in vivo exercise (Hintz et al 1982;Ivy et al 1987;Bangsbo et al 2001;Ferguson et al 2001;Krustrup et al 2003).…”