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My last few post have delved a little into some concepts surrounding fat loss. This post will continue to follow that trend. The last post explored what happens to the fatty acids after they are liberated. What we want to happen is for the FFA to get oxidized. So how do we burn these FFAs? We have a few different options available, this post will explore one of them.
What option is that?
EXERCISE!
I know this seems pretty obvious but I wanted to explore this a bit and see if there is any differences in how we exercise and if so if there was any way to manipulate it in order to maximize fat loss.
Once exercise is initiated, beta-adrenergic stimulation occurs and results in increased lipolysis. This is because exercise stimulates the release of the catecholamines epinephrine and norepinephrine.
If you recall from my previous post, an increased presence of the catecholamines leads to increase fatty acid mobilization. These fatty acids are released from adipose tissue and intramuscular stores and transported to tissues. During exercise they are transported to our muscle tissues, across the muscle membrane and inside the mitochondria to undergo oxidation.
So how do we increase the use of fatty acids for fuel? First, simply exercise more. It is well established that trained individuals store more intramuscular fat and use this more as their source of energy during exercise.
We already know fat loss is regulated in several different ways. Lipolysis is regulated by catecholamines and insulin. The transport of FFAs is regulated by blood flow (which coincidentally is also regulated by catecholamines to some extent). We also know the uptake and storage of them is somewhat improved by consistent exercise. Now what about fat oxidation. What factors affect this?
One of the most important factors that determine the rate of fat oxidation is exercise intensity. Most people would think this would be a more = better scenario, but there is somewhat of a paradox here. Unlike glucose oxidation, which increases proportionally with exercise intensity, fatty acid oxidation increases at low to moderate intensities but then decreases at higher intensities. Why is this?
There are a few things going on here. First, exercise increases norepinephrine output. This as we already know increases lipolysis. These free’d fatty acids are then transported to the muscles and are oxidized to meet the energy demands of the movement. Now as intensity increases, so does catecholamine output. This is great because this increases lipolysis even more, but unfortunately this does not result in more fatty acids getting oxidized. This happens for 2 reasons. First, the bodys preferential fuel source during high intensity is glucose, not fat. Second, high intensity exercise increases the release of lactate in the muscle and this lactate actually traps all the freed fatty acids in the muscle. Blood flow also changes. As intensity increases, blood flow to the muscles and skin is increased. This change limits the periphal blood flow. This is where the adipose tissues are so, there isn't enough flow to carry the FFAs away to the muscle tissue to get oxidized. Ultimately what all this means, is all that fat we mobilized ends up get stored again. For these reasons, I believe this is partially the reason why LISS is advocated for weight loss (other than the effect it has on recovery). But don’t lose hope, with some proper programming and timing we can manipulate exercise intensity levels to our advantage.
So how do we do this? We simply combine the intensities in a methodical manner. First we start with high intensity movements. This maximizes lipolysis. For this, HIIT is the best option. There are a few ways we can perform this and it is going to be highly dependent on the individual (due to a variation in VO2max between individuals).
Here is some examples you can use
Adapted from Bracken et al
Ten 6-second maximal effort sprints with a 30-second recovery between each sprint.
Adapted from Burgomaster et al
Three 30-second maximal effort sprints with 4.5 minutes of active recovery between sprints.
(this one may be a bit challenging for most)
Adapted from Trapp et al.
20 minutes of HIIT for 8s on and 12s off or 12s and 24s off.
After the HIIT work, you want to rest of about 5 minutes. This provides time so the now liberated fatty acids can enter the bloodstream. After we have been rested, now we want to engage in some lower intensity exercise so we can burn off all the FFAs floating around in our blood.
In papers published by Achten et al. and Jeukendrup et al. we see that the level of exercise intensity at which maximal fat oxidation occurs, varies between the individuals training status. The optimal intensity for fat oxidation in trained individuals is roughly 62-63% of VO2max or a more practical and useable measurement, 70-75% of HRmax. However, for untrained and less trained individuals 50% of VO2max was the optimal intensity for fat oxidation. So we can generalize this some and say the range for fat oxidation is at moderate intensities of 50-65%VO2max or in other words, between 66-82% of HRmax. So after resting from the HIIT work, we should engage in some aerobic exercise done at a moderate intensity for around 30-40 minutes. One last note about this, the mode of exercise has an effect on fat oxidation. For some reason, fatty acid oxidation is higher during walking and running, compared with cycling.
The benefits don’t stop there. Both forms of exercise described above will also improve several metabolic markers that will contribute to improved fat loss in the future.
What option is that?
EXERCISE!
I know this seems pretty obvious but I wanted to explore this a bit and see if there is any differences in how we exercise and if so if there was any way to manipulate it in order to maximize fat loss.
Once exercise is initiated, beta-adrenergic stimulation occurs and results in increased lipolysis. This is because exercise stimulates the release of the catecholamines epinephrine and norepinephrine.
If you recall from my previous post, an increased presence of the catecholamines leads to increase fatty acid mobilization. These fatty acids are released from adipose tissue and intramuscular stores and transported to tissues. During exercise they are transported to our muscle tissues, across the muscle membrane and inside the mitochondria to undergo oxidation.
So how do we increase the use of fatty acids for fuel? First, simply exercise more. It is well established that trained individuals store more intramuscular fat and use this more as their source of energy during exercise.
We already know fat loss is regulated in several different ways. Lipolysis is regulated by catecholamines and insulin. The transport of FFAs is regulated by blood flow (which coincidentally is also regulated by catecholamines to some extent). We also know the uptake and storage of them is somewhat improved by consistent exercise. Now what about fat oxidation. What factors affect this?
One of the most important factors that determine the rate of fat oxidation is exercise intensity. Most people would think this would be a more = better scenario, but there is somewhat of a paradox here. Unlike glucose oxidation, which increases proportionally with exercise intensity, fatty acid oxidation increases at low to moderate intensities but then decreases at higher intensities. Why is this?
There are a few things going on here. First, exercise increases norepinephrine output. This as we already know increases lipolysis. These free’d fatty acids are then transported to the muscles and are oxidized to meet the energy demands of the movement. Now as intensity increases, so does catecholamine output. This is great because this increases lipolysis even more, but unfortunately this does not result in more fatty acids getting oxidized. This happens for 2 reasons. First, the bodys preferential fuel source during high intensity is glucose, not fat. Second, high intensity exercise increases the release of lactate in the muscle and this lactate actually traps all the freed fatty acids in the muscle. Blood flow also changes. As intensity increases, blood flow to the muscles and skin is increased. This change limits the periphal blood flow. This is where the adipose tissues are so, there isn't enough flow to carry the FFAs away to the muscle tissue to get oxidized. Ultimately what all this means, is all that fat we mobilized ends up get stored again. For these reasons, I believe this is partially the reason why LISS is advocated for weight loss (other than the effect it has on recovery). But don’t lose hope, with some proper programming and timing we can manipulate exercise intensity levels to our advantage.
So how do we do this? We simply combine the intensities in a methodical manner. First we start with high intensity movements. This maximizes lipolysis. For this, HIIT is the best option. There are a few ways we can perform this and it is going to be highly dependent on the individual (due to a variation in VO2max between individuals).
Here is some examples you can use
Adapted from Bracken et al
Ten 6-second maximal effort sprints with a 30-second recovery between each sprint.
Adapted from Burgomaster et al
Three 30-second maximal effort sprints with 4.5 minutes of active recovery between sprints.
(this one may be a bit challenging for most)
Adapted from Trapp et al.
20 minutes of HIIT for 8s on and 12s off or 12s and 24s off.
After the HIIT work, you want to rest of about 5 minutes. This provides time so the now liberated fatty acids can enter the bloodstream. After we have been rested, now we want to engage in some lower intensity exercise so we can burn off all the FFAs floating around in our blood.
In papers published by Achten et al. and Jeukendrup et al. we see that the level of exercise intensity at which maximal fat oxidation occurs, varies between the individuals training status. The optimal intensity for fat oxidation in trained individuals is roughly 62-63% of VO2max or a more practical and useable measurement, 70-75% of HRmax. However, for untrained and less trained individuals 50% of VO2max was the optimal intensity for fat oxidation. So we can generalize this some and say the range for fat oxidation is at moderate intensities of 50-65%VO2max or in other words, between 66-82% of HRmax. So after resting from the HIIT work, we should engage in some aerobic exercise done at a moderate intensity for around 30-40 minutes. One last note about this, the mode of exercise has an effect on fat oxidation. For some reason, fatty acid oxidation is higher during walking and running, compared with cycling.
The benefits don’t stop there. Both forms of exercise described above will also improve several metabolic markers that will contribute to improved fat loss in the future.
