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Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals

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A Letter to the Editor to this article was published on 14 March 2022

A Letter to the Editor to this article was published on 14 March 2022

Abstract

Background

Increased muscle mitochondrial mass is characteristic of elite professional endurance athletes (PAs), whereas increased blood lactate levels (lactatemia) at the same absolute submaximal exercise intensities and decreased mitochondrial oxidative capacity are characteristics of individuals with low aerobic power. In contrast to PAs, patients with metabolic syndrome (MtS) are characterized by a decreased capacity to oxidize lipids and by early transition from fat to carbohydrate oxidation (FATox/CHOox), as well as elevated blood lactate concentration [La−] as exercise power output (PO) increases, a condition termed ‘metabolic inflexibility’.

Objective

The aim of this study was to assess metabolic flexibility across populations with different metabolic characteristics.

Methods

We used indirect calorimetry and [La−] measurements to study the metabolic responses to exercise in PAs, moderately active individuals (MAs), and MtS individuals.

Results

FATox was significantly higher in PAs than MAs and patients with MtS (p < 0.01), while [La−] was significantly lower in PAs compared with MAs and patients with MtS. FATox and [La−] were inversely correlated in all three groups (PA: r = −0.97, p < 0.01; MA: r = −0.98, p < 0.01; MtS: r = −0.92, p < 0.01). The correlation between FATox and [La−] for all data points corresponding to all populations studied was r = −0.76 (p < 0.01).

Conclusions

Blood lactate accumulation is negatively correlated with FATox and positively correlated with CHOox during exercise across populations with widely ranging metabolic capabilities. Because both lactate and fatty acids are mitochondrial substrates, we believe that measurements of [La−] and FATox rate during exercise provide an indirect method to assess metabolic flexibility and oxidative capacity across individuals of widely different metabolic capabilities.

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Authors and Affiliations

  1. Department of Physical Medicine and Rehabilitation, University of Colorado School of Medicine, Aurora, CO, USA

    Iñigo San-Millán

  2. CU Sports Medicine and Performance Center, 2150 Stadium Drive, 2nd Floor, Boulder, CO, 80309, USA

    Iñigo San-Millán

  3. Exercise Physiology Laboratory, Department of Integrative Biology, University of California, Berkley, CA, USA

    George A. Brooks

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Correspondence to Iñigo San-Millán.

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Iñigo San-Millán and George A. Brooks declare that they have no conflicts of interest that are directly relevant to the content of this article.

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San-Millán, I., Brooks, G.A. Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals. Sports Med 48, 467–479 (2018). https://doi.org/10.1007/s40279-017-0751-x

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