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Alteration in the lactate threshold with changes in substrate availability

J L Ivy, D L Costill, P J Van Handel

    International Journal of Sports Medicine
    |August 1, 1981
    PubMed
    Summary

    Substrate availability affects lactate threshold (LT) during exercise. High free fatty acids increase LT, while high glucose does not alter it, suggesting other factors beyond anoxia contribute to lactate production.

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    Area of Science:

    • Exercise Physiology
    • Metabolic Biochemistry

    Background:

    • The lactate threshold (LT) is a key indicator of endurance exercise capacity.
    • Lactate production during exercise is influenced by metabolic factors, but the precise mechanisms are debated.

    Purpose of the Study:

    • To investigate the impact of altered substrate availability (glucose and free fatty acids) on blood lactate accumulation and LT during ergometer cycling.
    • To explore the relationship between substrate availability, lactate kinetics, and the LT.

    Main Methods:

    • Nine participants underwent ergometer cycling tests under three conditions: control, high blood glucose, and high blood free fatty acids.
    • Blood lactate levels (HLa) and delta HLa were measured at various workloads.
    • Lactate threshold (LT) was determined as a percentage of VO2 max.

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    Main Results:

    • High blood glucose did not significantly change LT compared to control, although resting lactate was higher.
    • Elevated blood free fatty acids significantly reduced HLa and delta HLa at workloads between 150-250 W.
    • High free fatty acids significantly increased the LT (59.8% VO2max) compared to control (53.9% VO2max).

    Conclusions:

    • Lactate threshold is sensitive to changes in substrate availability during exercise.
    • Muscle tissue anoxia may not be the sole determinant of lactate production during submaximal exercise.
    • Free fatty acid availability appears to enhance endurance capacity by altering lactate metabolism.