Running 40 Minutes to Burn Fat?
During the dry phase, weight-training practitioners alternate muscle training and cardio to gradually reduce body fat, limiting muscle loss as much as possible. The goal is to get a drawn and muscular physique…
We often hear that you have to run at least 40 minutes to burn fat and that to lose weight, nothing serves to run fast. What is it really?
Should we make short and intense efforts or prolonged efforts to lose adipose tissue?
A misunderstood concept!
At rest, 25% to 50% of our energy expenditure is ensured by the burning of free fatty acids. How does this change during the effort?
During a short effort in intense, it is the carbohydrates (sugars) that provide the energy. The more intense our efforts, the less our ability to use our fat. This would result from a lower re-esterification of fatty acids as the intensity increases (making them less available).
Lipids therefore provide energy during long and light efforts.
Precisely, they would provide 50 to 60% of the energy for intensities lower than 65% of the VO2 max, and more than 10 to 45% for an intensity between 65 and 80% VO2 max. This is very well illustrated by Brooks and Mercier’s cross-over point concept (see below).
The famous “crossover point” of Brooks and Mercier (1994).
However this concept is nuanced by Brooks himself (1997) who specify that such values are indicative, and can vary greatly depending on age, gender and level of training.
The trained subjects use their body fat more, thus sparing muscle and hepatic (liver) glycogen (sugar) for more intense efforts. This is due to a capillarization (creation of an arteriovenous network, allowing to circulate the fats and thus to mobilize them) and to the increase the activity of the LPL (lipoprotein lipase) and the enzymes which help the beta-oxidation (the oxidation of lipids).
We should spend about 15 kcal / kg per week to change the profile of lipoproteins and therefore act favorably on our adipose tissue. For a man of 70 kg it corresponds to 1050 kcal, two to three outputs running depending on the time and speed.
The information is poorly understood, it is not about running forty minutes to burn fat, but to maintain an intensity that allows us to hold at least forty minutes! Below this, the high intensity will choose carbohydrates as a source of energy.
Today we are talking about HIIT or High Intensity Interval Training, which would have miracle effects on weight loss. It’s not hard to imagine running for ten to twenty seconds every thirty seconds for fifteen minutes to dry. As well as run ten 400 meters at full speed.
But we have just seen that the mobilization of fat is mainly done during long efforts and medium intensity. It was not counting on the EPOC phenomenon (Excess Post Exercise Oxygene Consumption)!
The EPOC phenomenon defines post-exercise oxygen consumption in order to replenish reserves. Thus, in order to return all the body parameters to the state of rest (ATP, creatine phosphate, lactates …) the body needs energy. Energy fired … free fatty acids! EPOC contributes 10% of the total energy cost of the exercise. Also, the EPOC depends both on the duration and the intensity of the exercise, but it has been shown that it is primarily the intensity of the exercise that influenced this phenomenon (Børsheim, 2003).
Finally, a short and intensive effort draws its energy from carbohydrates as seen above. But the repetition of these efforts (as in the HIIT) gradually pushes the body towards an aerobic functioning, which favors fats as an energetic substrate.
Short and intense efforts would be just as beneficial for the loss of fat tissue as prolonged efforts. But this is to be relativized for two reasons:
– As seen in the first part, prolonged efforts improve the ability to use fats as fuel.
– A fundamental endurance work is necessary before moving towards higher intensities.
” It’s important to develop basic stamina before performing quality sessions. There is no point in having a powerful heart pump if the system of transporting blood to the muscle cells is not effective. Jack Arnault, Federal Coach of Athletics.