Understanding the factors that effect maximal fat oxidation

Abstract

Lipids as a fuel source for energy supply during submaximal exercise originate from subcutaneous adipose tissue derived fatty acids (FA), intramuscular triacylglycerides (IMTG), cholesterol and dietary fat. These sources of fat contribute to fatty acid oxidation (FAox) in various ways. The regulation and utilization of FAs in a maximal capacity occur primarily at exercise intensities between 45 and 65% VO2max, is known as maximal fat oxidation (MFO), and is measured in g/min. Fatty acid oxidation occurs during submaximal exercise intensities, but is also complimentary to carbohydrate oxidation (CHOox). Due to limitations within FA transport across the cell and mitochondrial membranes, FAox is limited at higher exercise intensities. The point at which FAox reaches maximum and begins to decline is referred to as the crossover point. Exercise intensities that exceed the crossover point (~65% VO2max) utilize CHO as the predominant fuel source for energy supply. Training status, exercise intensity, exercise duration, sex differences, and nutrition have all been shown to affect cellular expression responsible for FAox rate. Each stimulus affects the process of FAox differently, resulting in specific adaptions that influence endurance exercise performance. Endurance training, specifically long duration (>2 h) facilitate adaptations that alter both the origin of FAs and FAox rate. Additionally, the influence of sex and nutrition on FAox are discussed. Finally, the role of FAox in the improvement of performance during endurance training is discussed.

The influence of cardiorespiratory fitness on clustered cardiovascular disease risk factors and the mediator role of body mass index in youth: The UP&DOWN Study

“…Previously, CRF has been negatively associated with adiposity in youth, and it is considered a predictor of adiposity in later years . The physiological mechanisms by which CRF affects adiposity may include the effect that aerobic exercise exerts on the expression and activity of carnitine palmitoyl transferase I (an enzyme that controls the fatty acids movement into the mitochondria), as well as the increase in β‐Hydroxy acyl‐CoA dehydrogenase protein expression (a key enzyme that regulates fat oxidation) . On the other hand, adipose tissue produces several adipokines involved in inflammation .…”

“…5,7,38 The physiological mechanisms by which CRF affects adiposity may include the effect that aerobic exercise exerts on the expression and activity of carnitine palmitoyl transferase I (an enzyme that controls the fatty acids movement into the mitochondria), as well as the increase in β-Hydroxy acyl-CoA dehydrogenase protein expression (a key enzyme that regulates fat oxidation). 39 On the other hand, adipose tissue produces several adipokines involved in inflammation. 40 Obesity-induced inflammation is well known for being responsible of several cardiometabolic disorders, including insulin resistance;…”

Carnitine in Human Muscle Bioenergetics: Can Carnitine Supplementation Improve Physical Exercise?

“…Different studies have been conducted to explain the regulatory points influencing the decline of fatty acid oxidation in skeletal muscle during high-intensity endurance exercise [62][63][64]. Considering that carnitine is necessary for the transmembrane fatty acid transport, changes in the muscle free carnitine availability may contribute to the regulation of fatty acid oxidation.…”

Multidisciplinary lifestyle intervention in children and adolescents - results of the project GRIT (Growth, Resilience, Insights, Thrive) pilot study

“…Based on the calculated respiratory quotient (VCO 2 /VO 2 ), fat and carbohydrate oxidation and energy expenditure were calculated using stoichiometric equations and appropriate energy equivalents, with the assumption that the urinary nitrogen excretion rate was negligible during the treadmill test [36,40]. Maximum fat oxidation (MFO) [41] was calculated in kcal/min based on the highest fat oxidation measure within the 1-min testing increments calculated during the exercise test. MFO time was also recorded as the 1min testing increment within which the MFO measure occurred.…”