Skeletal muscle biochemical origin of exercise intensity domains and their relation to whole-body V̇O2 kinetics. Issue 8 (31st August 2022)

• Record Type: Journal Article
• Authors: Korzeniewski, Bernard; Rossiter, Harry B.
• Is Part Of: Bioscience reports. Volume 42:Issue 8(2022)
• Publication Date: 2022-08-31
• Subjects: blood lactate -- exercise intensity -- inorganic phosphate -- muscle fatigue -- oxygen consumption -- skeletal muscle; Molecular biology -- Periodicals; Cytology -- Periodicals; 572.8
• DOI: 10.1042/BSR20220798
• Languages: English
• ISSNs: 0144-8463

Abstract

Abstract: This article presents the biochemical intra-skeletal-muscle basis of exercise intensity domains: moderate (M), heavy (H), very heavy (VH) and severe (S). Threshold origins are mediated by a 'Pi double-threshold' mechanism of muscle fatigue, which assumes (1) additional ATP usage, underlying muscle V̇O2 and metabolite slow components, is initiated when inorganic phosphate (Pi ) exceeds a critical value (Picrit ); (2) exercise is terminated because of fatigue, when Pi reaches a peak value (Pipeak ); and (3) the Pi increase and additional ATP usage increase mutually stimulate each other forming a positive feedback. M/H and H/VH borders are defined by Pi on-kinetics in relation to Picrit and Pipeak . The values of the ATP usage activity, proportional to power output (PO), for the M/H, H/VH and VH/S borders are lowest in untrained muscle and highest in well-trained muscle. The metabolic range between the M/H and H/VH border (or 'H space') decreases with muscle training, while the difference between the H/VH and VH/S border (or 'VH space') is only weakly dependent on training status. The absolute magnitude of the muscle V̇O2 slow-component, absent in M exercise, rises gradually with PO to a maximal value in H exercise, and then decreases with PO in VH and S exercise. Simulations of untrained, physically active and well-trained muscle demonstrate that the muscle M/H border need not be identical to the whole-body M/H border determined from pulmonary V̇O2 on-kinetics and blood lactate, while suggesting that the biochemical origins of the H/VH border reside within skeletal muscle and correspond to whole-body critical power.