Noninvasive determination of exercise-induced hydrodgen ion threshold through direct optical measurement

• Published in: Journal of applied physiology (1985) Vol. 104; no. 3; pp. 837 - 844
• Main Authors: Soller, Babs R, Yang, Ye, Lee, Stuart M. C, Wilson, Cassie, Hagan, R. Donald
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.03.2008; American Physiological Society
• Subjects: Adult; Anaerobic Threshold; Biological and medical sciences; Blood; Carbon dioxide; Exercise; Exercise - physiology; Extracellular Fluid - metabolism; Feasibility Studies; Female; Fundamental and applied biological sciences. Psychology; Gas exchange; Hand Strength; Humans; Hydrogen; Hydrogen ion concentration; Hydrogen ions; Ions; Lactic Acid - metabolism; Male; Models, Biological; Muscle Contraction; Muscle, Skeletal - metabolism; Oxygen; Oxygen Consumption; Oxygen uptake; Pulmonary Gas Exchange; Quadriceps Muscle - metabolism; Spectroscopy, Near-Infrared; Spectrum analysis; United States; United States; Physical exercise; near-infrared spectroscopy; Cyclism; Carbon dioxide; cycling; Lactates; Optical measurement; Sport; Vertebrata; Mammalia; Anaerobic threshold; pH; lactate
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00849.2007

1 Department of Anesthesiology, University of Massachusetts Medical School, Worcester, Massachusetts; and 2 Wyle Laboratories, 3 JES Tech, and 4 National Aeronautic and Space Administration Johnson Space Center, Houston, Texas Submitted 7 August 2007 ; accepted in final form 14 December 2007 The intensity of exercise above which oxygen uptake ( O 2 ) does not account for all of the required energy to perform work has been associated with lactate accumulation in the blood (lactate threshold, LT) and elevated carbon dioxide output (gas exchange threshold). An increase in hydrogen ion concentration ([H + ]) is approximately concurrent with elevation of blood lactate and CO 2 output during exercise. Near-infrared spectra (NIRS) and invasive interstitial fluid pH (pHm) were measured in the flexor digitorum profundus during handgrip exercise to produce a mathematical model relating the two measures with an estimated error of 0.035 pH units. This NIRS pHm model was subsequently applied to spectra collected from the vastus lateralis of 10 subjects performing an incremental-intensity cycle protocol. Muscle oxygen saturation (SmO 2 ) was also calculated from spectra. We hypothesized that a H + threshold could be identified for these subjects and that it would be different from but correlated with the LT. Lactate, gas exchange, SmO 2 , and H + thresholds were determined as a function of O 2 using bilinear regression. LT was significantly different from both the gas exchange threshold ( = 0.27 ± 0.29 l/min) and H + threshold ( = 0.29 ± 0.23 l/min), but the gas exchange threshold was not significantly different from the H + threshold ( = 0.00 ± 0.38 l/min). The H + threshold was strongly correlated with LT ( R 2 = 0.95) and the gas exchange threshold ( R 2 = 0.85). This initial study demonstrates the feasibility of noninvasive pHm estimations, the determination of H + threshold, and the relationship between H + and classical metabolic thresholds during incremental exercise. pH; anaerobic threshold; near-infrared spectroscopy; cycling; lactate; carbon dioxide Address for reprint requests and other correspondence: B. R. Soller, Dept. of Anesthesiology, Univ. of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (e-mail: babs.soller{at}umassmed.edu )