Macro partitioning
Increasing exercise intensity above approximately 75% VO2max downregulates fat oxidation due to decreased adipose blood flow, reduced FFA delivery, and intramuscular inhibition of fatty acid transport and oxidation.
If your goal is to maximize the amount of fat you burn *during* your workout, keep your intensity moderate (around 60-65% of your max oxygen uptake). If you exercise at very high intensities (above 75% VO2max), your body switches to burning mostly carbohydrates because it can't deliver and process fat fast enough to meet the energy demand.
Fat oxidation increases from rest to low- and moderate-intensity exercise (maximum at ~60–65 % VO2max), but decreases at power outputs above approximately 75 % VO2max [29–31]. ... The release of FFAs is decreased from adipose tissue at higher intensities of exercise, most likely due to reduced adipose tissue blood flow, resulting in decreased delivery of FFAs to the contracting muscle.
Why this rating
Supported by multiple studies (refs 29-31, 32, 33) showing consistent trends in human skeletal muscle.
Source
New Insights into the Interaction of Carbohydrate and Fat Metabolism During Exercise
Lawrence L. Spriet · Sports Medicine · 2014
DOI 10.1007/s40279-014-0154-1
More from this paper
- Increasing carbohydrate availability (via glucose ingestion or high glycogen stores) reciprocally downregulates fat oxidation in skeletal muscle during exercise through insulin-mediated suppression of adipose lipolysis and direct inhibition of fatty acid transport proteins.Good
- Increasing fat availability (via elevated plasma free fatty acids) downregulates carbohydrate oxidation in skeletal muscle during exercise, primarily by inhibiting glycogen phosphorylase (PHOS) activity through reduced accumulation of ADP and AMP.Good
Related findings · Macro partitioning
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- Resistance exercise training combined with sufficient dietary protein intake acts synergistically to maximize skeletal muscle hypertrophy, with protein intake saturating around 1.6 g/kg/day for general populations and potentially requiring 2.0-2.2 g/kg/day for resistance-trained individuals.Strong
- Trans fats should be completely eliminated from the diet, as they increase LDL cholesterol, decrease HDL cholesterol, and are directly associated with increased coronary risk.Strong
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