Determinants of Gas Exchange and Acid–Base Balance During Exercise

Johnson, Robert L.; Heigenhauser, George J. F.; Hsia, Connie C. W.; Jones, Norman L.; Wagner, Peter D.

doi:10.1002/cphy.cp120112

Cited by 52 publications

(61 citation statements)

References 217 publications

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“…Since maximal lactate levels also remained unchanged throughout the three periods, our results suggest that the body's general buffering capacity at maximal or near-maximal workloads is not affected by training. Despite the present limitation of the use of venous blood, it has been suggested that at high workloads, variables such as hydrogen ion concentration tend to be identical in arterial and venous blood [25]. A major drawback, however, stems from the fact that we did not specifically measure muscle buffering capacity as Weston and co-workers [11] did.…”

Section: Discussionmentioning

confidence: 89%

Metabolic and Neuromuscular Adaptations to Endurance Training in Professional Cyclists. A Longitudinal Study.

Lucía

Hoyos²,

Pardo³

et al. 2000

JJP

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Professional road cycling is an extreme endurance sport. Approximately 30,000-35,000 km are cycled each year and the racing season of professional riders includes ϳ90 competition days. In addition, despite the long duration of cycling events such as 3-week stage races, the relative contribution of intense exercise is surprisingly high during the more physically taxing events (mountain passes, time trials, sprints, "breakaways" etc.) [1].Several investigators have analyzed a number of physiological variables in professional cyclists, both in laboratory [2][3][4][5][6][7] and field settings [1,[8][9][10]. However, no prospective, long-term investigation has established the specific physiological adaptations which occur in professional cyclists as a response to training and competition during a typical sports season (generally including different periods in terms of training volume and/or intensity; i.e., precompetition or training, competition, and postcompetition or "active" rest periods). In a recent study (unpublished data), we found no overall training-effect on the ventilatory response (i.e., pulmonary ventilation, tidal volume, ventilatory equivalents, "timing" of respiration, etc.) in the same 13 subjects who formed the present study population. It was therefore considered of interest to extend this investigation to determine whether meta- ]. Finally, rms-EMG tended to increase during the season, with significant differences (pϽ0.05) observed mainly between the competition and rest periods at most workloads. In contrast, precompetition MPF values increased (pϽ0.05) with respect to resting values at most submaximal workloads but fell (pϽ0.05) during the competition period. Our findings suggest that endurance conditioning induces the following general adaptations in elite athletes: (1) lower circulating lactate and increased reliance on aerobic metabolism at a given submaximal intensity, and possibly (2) an enhanced recruitment of motor units in active muscles, as suggested by rms-EMG data.

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Section: Discussionmentioning

confidence: 89%

Metabolic and Neuromuscular Adaptations to Endurance Training in Professional Cyclists. A Longitudinal Study.

Lucía

Hoyos²,

Pardo³

et al. 2000

JJP

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“…The following equation expresses the relative contribution in a simple cell model (Groebe, 1995;Johnson et al, 1996): where P O2 partial pressure of O 2 , f O2 overall O 2 flux density, f O2 MbO 2 flux density based on Mb-facilitated diffusion, f O2 O2O 2 flux density from free O 2 , K 0 Krogh's diffusion constant for free O 2 , D Mb Mb translational diffusion coefficient, C Mb Mb concentration in the cell, P 50 the P O2 that half-saturates Mb, which reflects the O 2 binding affinity of Mb.…”

Section: Contribution Of Mb-facilitated Versus Free O 2 Transportmentioning

confidence: 99%

Myoglobin's old and new clothes: from molecular structure to function in living cells

Gros

Wittenberg

Jue

2010

Journal of Experimental Biology

102

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SUMMARY Myoglobin, a mobile carrier of oxygen, is without a doubt an important player central to the physiological function of heart and skeletal muscle. Recently, researchers have surmounted technical challenges to measure Mb diffusion in the living cell. Their observations have stimulated a discussion about the relative contribution made by Mb-facilitated diffusion to the total oxygen flux. The calculation of the relative contribution, however, depends upon assumptions, the cell model and cell architecture, cell bioenergetics, oxygen supply and demand. The analysis suggests that important differences can be observed whether steady-state or transient conditions are considered. This article reviews the current evidence underlying the evaluation of the biophysical parameters of myoglobin-facilitated oxygen diffusion in cells, specifically the intracellular concentration of myoglobin, the intracellular diffusion coefficient of myoglobin and the intracellular myoglobin oxygen saturation. The review considers the role of myoglobin in oxygen transport in vertebrate heart and skeletal muscle, in the diving seal during apnea as well as the role of the analogous leghemoglobin of plants. The possible role of myoglobin in intracellular fatty acid transport is addressed. Finally, the recent measurements of myoglobin diffusion inside muscle cells are discussed in terms of their implications for cytoarchitecture and microviscosity in these cells and the identification of intracellular impediments to the diffusion of proteins inside cells. The recent experimental data then help to refine our understanding of Mb function and establish a basis for future investigation.

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“…This might have particular significance for diving mammals or animals enduring prolonged periods of hypoxic stress because the solubility of O 2 is quite low (Johnson et al, 1996). In the myocardium, the basal P O 2 of 10mmHg in myocytes represents only about 13moll -1 O 2 .…”

Section: Other Functions Of Mb Poresmentioning

confidence: 99%

“…10mmHg, the concentration of Mb-bound O 2 (260moll -1 ) in rat heart stands about 20 times higher than the level of free O 2 (13moll -1 ) (Masuda et al, 2008). Even though free O 2 diffuses more rapidly than Mb, the concentration difference between free O 2 and Mb-bound O 2 can still confer a significant role for Mb in contributing to the overall O 2 flux if Mb has sufficient diffusive mobility in the cell (Gros et al, 2010;Johnson et al, 1996). No theoretical or experimental evidence supports any direct transfer of O 2 from one myoglobin molecule to another in a 'bucket brigade' fashion (Gibson, 1959).…”

Section: Introductionmentioning

confidence: 95%

‘It's hollow’: the function of pores within myoglobin

Tomita

Kreutzer

Adachi

et al. 2010

Journal of Experimental Biology

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SUMMARY Despite a century of research, the cellular function of myoglobin (Mb), the mechanism regulating oxygen (O2) transport in the cell and the structure–function relationship of Mb remain incompletely understood. In particular, the presence and function of pores within Mb have attracted much recent attention. These pores can bind to Xe as well as to other ligands. Indeed, recent cryogenic X-ray crystallographic studies using novel techniques have captured snapshots of carbon monoxide (CO) migrating through these pores. The observed movement of the CO molecule from the heme iron site to the internal cavities and the associated structural changes of the amino acid residues around the cavities confirm the integral role of the pores in forming a ligand migration pathway from the protein surface to the heme. These observations resolve a long-standing controversy – but how these pores affect the physiological function of Mb poses a striking question at the frontier of biology.

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Determinants of Gas Exchange and Acid–Base Balance During Exercise

Cited by 52 publications

References 217 publications

Metabolic and Neuromuscular Adaptations to Endurance Training in Professional Cyclists. A Longitudinal Study.

Metabolic and Neuromuscular Adaptations to Endurance Training in Professional Cyclists. A Longitudinal Study.

Myoglobin's old and new clothes: from molecular structure to function in living cells

‘It's hollow’: the function of pores within myoglobin

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