Extracellular bicarbonate and non-bicarbonate buffering against lactic acid during and after exercise |
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Authors: | Dieter Böning Carola Klarholz Bärbel Himmelsbach Matthias Hütler Norbert Maassen |
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Institution: | (1) Institute of Sports Medicine, Charité - University Medicine Berlin, Berlin, Germany;(2) BE Sports Physiology/Sports Medicine, Medical School Hannover, Hannover, Germany;(3) Sports Medicine, Charité, University Medicine Berlin, Arnimallee 22, 14195 Berlin, Germany |
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Abstract: | Defense of extracellular pH constancy against lactic acidosis can be estimated from changes (Δ) in lactic acid (La]), HCO3−], pH and PCO2 in blood plasma because it is equilibrated with the interstitial fluid. These quantities were measured in earlobe blood during
and after incremental bicycle exercise in 13 untrained (UT) and 21 endurance-trained (TR) males to find out if acute and chronic
exercise influence the defense. During exercise the capacity of non-bicarbonate buffers (βnbi = −ΔLa] · ΔpH−1 − ΔHCO3−] · ΔpH−1) available for the extracellular fluid (mainly hemoglobin, dissolved proteins and phosphates) amounted to 32 ± 2(SEM) and
20 ± 2 mmol l−1 in UT and TR, respectively (P < 0.02). During recovery βnbi decreased to 14 (UT) and 12 (TR) mmol l−1 (both P < 0.001) corresponding to values previously found at rest by in vivo CO2 titration. Bicarbonate buffering (βbi) amounted to 44–48 mmol l−1 during and after exercise. The large exercise βnbi seems to be mainly caused by an increasing concentration of all buffers due to shrinking of the extracellular volume, exchange
of small amounts of HCO3− or H+ with cells and delayed HCO3− equilibration between plasma and interstitial fluid. Increase of HCO3−] during titration by these mechanisms augments total β and thus the calculated βnbi more than βbi because it reduces ΔpH and ΔHCO3−] at constant ΔLa]. The smaller rise in exercise βnbi in TR than UT may be caused by an increased extracellular volume and an improved exchange of La−, HCO3− and H+ between trained muscles and blood. |
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Keywords: | Acid– base status Erythrocytes Physical training Respiratory compensation |
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