Exercise and caloric restriction are a proven combination to reduce scale weight. The real key, however, is to reduce excess body fat – subcutaneous (under the skin), visceral (around vital organs), and ectopic (within the organs).
From an exercise perspective, it’s all about frequency, intensity, and time – the “fit principle.” Of the three variables, the appropriate intensity to optimize fat max – maximal fat burning – requires testing or the use of heart rate percentages that estimate fat max.
When exercising, the primary energy sources are derived from a percentage of fat and carbohydrate – depending on the intensity of exercise. The higher intensity the less fat is used and vice versa. The fat max zone can be determined via a VO2 Max test correlated to a percentage of maximum heart rate.
The V stands for volume, and the O2 is the chemical formula for oxygen we breathe. Your VO2 at the stage of maximal exertion is called your maximal oxygen consumption (VO2 max). The test is usually performed in a laboratory by a trained medical professional.
The VO2 Max test measures milliliters of oxygen per kilogram of body weight (1 kilogram = 2.2 pounds) used per minute. By measuring VO2 max relative to body weight, we are able to determine endurance and stamina levels. Then, we can relate this to a heart rate at any point during the test.
For max heart rate (HRmax) determination, the age-predicted HRmax formula used by the American College of Sports Medicine (ACSM) is 220–age.
According to research - Fat Oxidation Rate As a Function of Plasma Lipid and Hormone Response in Endurance Athletes - which appeared in the January 2020 issue of the Journal of Strength and Conditioning Research, “the regulation of adipose (fat) tissue lipolysis (breakdown) and the release of FFAs (free fatty acids) from adipose tissue to the muscle is an important route of control for fat oxidation (burning).”
Researchers from Spain sought to investigate, “the relationship among fat oxidation rate, plasma lipids (total cholesterol, triglycerides, HDL good cholesterol, and LDL bad cholesterol), and hormone concentrations (adrenaline, noradrenaline, catecholamine, insulin) in well-trained athletes.”
The Spanish investigators recruited twenty-six trained triathletes, who completed a graded stationary cycle test to exhaustion - increasing the intensity every 10 minutes. Fat oxidation rates were determined using the indirect calorimetry method.
Each individual’s maximal fat oxidation (MFO) rate - the intensity at which MFO occurred (fat max), and the intensity at which fat oxidation became minimal (fat min) were determined. Blood samples for lipid and hormone analysis were collected at the end of each stage of the graded exercise test.
It was determined that the fat oxidation rate became significant at 60% of VO2 max or 75% of HRmax, while maximizing at 70% of VO2 max or roughly 80% HRmax. As an individual reaches their VO2 max, they approach their HRmax.
From a lipid and hormone perspective, the researchers determined that, “low-density lipoprotein (LDL) and triglycerides (TG) decreased and showed lowest levels at 60%VO2max and reaching significant increases after 80%VO2max. High-density lipoprotein (HDL) reached significant increase at 60%VO2max. Adrenaline and noradrenaline increased until the end of the incremental exercise, and significant differences were from 50%VO2max.”
The take-away message is that fat burns in the flame of oxygen at roughly 70-80% HRmax. From my experience, I have found the lower end of the range starts at 55% of HRmax.
Subtract your age from 220. Then take 55 and 80% for your lower and upper fat max training zone – ideally staying closer 70%, as the higher number.
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