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    AN EVALUATION OF LACTATE AND RESPIRATORY RESPONSES TO INCREMENTAL AND CONSTANT LOAD WORK BOUTS.

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    Author
    CONSTABLE, STEFAN HARRY.
    Issue Date
    1982
    Keywords
    Exercise -- Physiological aspects.
    Lactic acid.
    Treadmill exercise tests.
    Respiration.
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    An attempt was made to evaluate the applicability of a theorized model concerning plasma lactic acid kinetics to running performance assessment. This model incorporated two distinct lactate thresholds identified as the aerobic threshold (AerT) and the anaerobic threshold (AT). Two groups of males with different levels of fitness were tested. Group 1 (n = 5) consisted of recreational athletes (͞X VO₂ max = 49.3 ml/kg•min⁻¹) who ran less than 20 miles per week, while Group 2 (n = 6) were highly trained runners (͞X VO₂ max = 65.5 ml/kg•min⁻¹) who all ran at least 40 miles per week. All subjects participated in two incremental work load (IWL) and four constant work load (CWL) tests that consisted of horizontal treadmill running at different speeds. The IWL tests elicited linear increases in VO₂ and were highly correlated for both Group 1 (r = .986) and Group 2 (r = .999). However, three unbiased observers found the identification of both AerT and AT, using independent lactate and respiratory gas exchange "breakpoints," very subjective in nature. The test-retest reliablity was generally poor and varied considerably among both the observers and the individual predictor variables. The validity of the respiratory gas exchange predictors was then evaluated against the criterion lactate thresholds using the estimates of a fourth, more experienced observer. The resultant correlation coefficients were generally not high, while t-test evaluation demonstrated significant (p < .05) differences in fifty percent of the cases. This same observer then pooled all of the ventilatory predictors in an effort to better estimate both AerT and AT indirectly. These indirect ventilatory estimates consistently underpredicted the criterion lactate thresholds. This finding suggests that increases in running speeds may confound the normal associate between plasma lactate and ventilation at increasing work levels. Arbitrary lactate concentrations of 2mmol/2 and 4 mmol/L were further evaluated as threshold predictors. This methodology consistently overpredicted the criterion lactate thresholds in terms of VO₂. When any of these AerT and AT threshold estimates were compared to the lactate responses during the appropriate CWL test, no meaningful relationship were found. These observations question the physiological significance of both AerT and AT evaluation during treadmill running, as well as pointing out the difficulty in reliably detecting both plasma lactate thresholds regardless of the methodology.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Animal Physiology
    Graduate College
    Degree Grantor
    University of Arizona
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