Friday, October 11, 2013

Do you lose muscle if you lift weights after a 24-hour fast? Probably not if you do that regularly

Compensatory adaptation (CA) is an notion that is beneficial in the understanding of how the human body reacts to inputs like dietary ingestion of macronutrients and physical exercise. CA is a sophisticated process, since it requires suggestions loops, but it leads to adaptations that are relatively basic, making use of to a massive cross-part of the populace.

A joke amongst software program builders is that the computer does exactly what you tell it to do, but not automatically what you want it to do. In the same way, via CA your physique responds specifically to the inputs you give it, but not automatically in the way you would like it to react. For instance, a average caloric deficit might direct to gradual entire body fat decline, while a very substantial caloric deficit may possibly provide physique unwanted fat loss to a halt.

Energy instruction would seem to direct to various adaptations, which can be understood through the lens presented by CA. A single of them is a remarkable improve in the potential of the human body to retailer glycogen, in each liver and muscle mass. Glycogen is the main gasoline used by muscle during anaerobic physical exercise. Standard energy instruction brings about, above time, glycogen retailers to far more than double. And about two.six the volume of glycogen is also stored as drinking water.

When one particular appears greater and gets to be more powerful as a outcome of toughness training, that is in no tiny portion because of to boosts in glycogen and h2o saved. Far more glycogen saved in muscle sales opportunities to a lot more toughness, which is essentially a evaluate of one’s capacity to shift a particular amount of fat about. More muscle mass protein is also connected with far more energy.

Contemplating in phrases of CA, the improve in the body’s capability to store glycogen is to be envisioned, as extended as glycogen stores are depleted and replenished on a normal basis. By performing toughness training routinely, you are telling your body that you need to have a good deal of glycogen on a standard foundation, and the body responds. But if you do not replenish your glycogen retailers on a standard foundation, you are also sending your human body a conflicting message, which is that nutritional sources of the substances employed to make glycogen are not conveniently obtainable. Amongst the substances that are utilized to make glycogen, the very best appears to be the mixture of fructose and glucose that a single finds in fruits.

Allow us suppose a a hundred and sixty-lbs untrained individual, John, who stored about 100 g of glycogen in his liver, and about five hundred g in his muscle cells, before beginning a energy education program. Let us believe, conservatively, that after 6 months of training he improved the measurement of his liver glycogen tank to one hundred fifty g. Muscle glycogen storage was also increased, but that is less appropriate for the dialogue in this put up.

Then John fasted for 24 several hours prior to a toughness instruction session, just to see what would happen. While fasting he went about his company, undertaking light actions, which led to a caloric expenditure of about a hundred energy for every hour (equivalent to 2400 for every working day). About 20 % of that, or 20 energy for each hour, came from a combination of blood glucose and ketones. Opposite to well-known belief, ketones can constantly be found in circulation. If only glucose have been utilised, five g of glucose for every hour would be required to offer individuals 20 calories.

In the course of the rapidly, John’s glucose requirements, driven largely by his brain’s requirements, have been achieved by conversion of liver glycogen to blood glucose. His muscle mass glycogen was pretty a lot “locked” during the quickly due to the fact he was carrying out only gentle routines, which depend primarily on body fat as gas. Muscle glycogen is “unlocked” via anaerobic physical exercise, of which power instruction is an occasion.

One of the roles of ketones is to spare liver glycogen, delaying the use of muscle protein to make glucose down the road, so the percentage of ketones in circulation in John’s human body enhanced in a way that was inversely proportional to saved liver glycogen. According to this review, following seventy two hrs fasting about 25 per cent of the body’s glucose needs are met by ketones. (This could be an underestimation.)

If we suppose a linear increase in ketone focus, this qualified prospects to a .69 % improve in circulating ketones for every single 2-hour period. (This is a simplification, as the improve is really very likely nonlinear.) So, when we seem at John’s liver glycogen tank, it possibly went down in a way related to that depicted on the figure beneath. The blue bars display liver glycogen at the finish of each two-hour interval. The pink bars present the approximate amount of glucose consumed in the course of every 2-hour time period. Glucose eaten goes down as liver glycogen decreases, since of the boost in blood ketones.

As you can see, soon after a 24-hour rapidly, John had about 35 g of glycogen still left, which is sufficient for a couple of extra hours of fasting. At the 24-hour mark the body had no need to have to be making use of muscle mass protein to make glucose. Maybe some of that occurred, but most likely not a lot if John was comfortable throughout the fast. (If he was pressured out, stress hormones would have enhanced blood glucose launch considerably.) From the body’s standpoint, muscle mass is “expensive”, whilst human body unwanted fat is “cheap”. And entire body excess fat, transformed to totally free fatty acids, is what is employed to produce ketones throughout a fast.

Blood ketone concentration does not go up substantially throughout a 24-hour rapidly, but it does following a 48-hour fast, when it becomes about 10 occasions larger. This significant improve happens mainly to spare muscle, which includes coronary heart muscle. If the increase is a lot more compact in the course of a 24-hour quickly, one can fairly presume that the human body is not going to be making use of muscle mass in the course of the fast. It can nonetheless depend on liver glycogen, collectively with a reasonably little sum of ketones.

Then John did his toughness training, after the 24-hour quick. When he did that, the muscles he utilised in the exercising session converted domestically stored glycogen into lactate. A flood of lactate was secreted into the bloodstream, which was utilized by his liver to generate glucose and also to replenish liver glycogen a little bit. Once more, at this stage there was no require for John’s body to use muscle mass protein to create glucose.

Counterintuitive as this may audio, the a lot more different muscles John utilised, the more lactate was made offered. If John did twenty sets of isolated bicep curls, for example, his entire body would not have launched ample lactate to satisfy its glucose requirements or replenish liver glycogen. As a end result, tension hormones would go up a whole lot, and his physique would deliver him some alarm indicators. A single of these alerts is a feeling of “pins and needles”, which is at times confused with the signs and symptoms of a heart assault.

John labored out a variety of muscle mass groups for thirty minutes or so, and he did not even truly feel fatigued. He felt energetic, in portion simply because his blood glucose went up a good deal, peaking at one hundred fifty mg/dl, to meet muscle needs. This elevated blood glucose was brought on by his liver producing blood glucose based mostly on lactate and releasing it into his blood. Muscle glycogen was depleted as a outcome of that.

Do you get rid of any muscle mass if you raise weights soon after a 24-hour rapidly?

I do not consider so, if you deplete your glycogen shops by undertaking energy education on a standard foundation, and also replenish them on a typical basis. In reality, your liver glycogen tank will boost in dimension, and you may possibly discover your self currently being in a position to fast for many several hours with no sensation hungry.

You will come to feel hungry after the strength coaching session subsequent the fast although possibly ravenous.


Brooks, G.A., Fahey, T.D., & Baldwin, K.M. (2005). Physical exercise physiology: Human bioenergetics and its apps. Boston, MA: McGraw-Hill.

Wilmore, J.H., Costill, D.L., & Kenney, W.L. (2007). Physiology of sport and physical exercise. Champaign, IL: Human Kinetics.
Title: Do you lose muscle if you lift weights after a 24-hour fast? Probably not if you do that regularly
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