Why do we go flabby when we stop exercising?
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El Greco
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Basically the mechanisms of muscle growth are what sickstan described, with these clarifications:
1) There's sarcomere ("functional") hypertrophy (growth of the contractile components of the muscle) and sarcoplasmic ("non-functional") hypertrophy (growth of the sarcoplasm and the sarcoplasmic reticulum). The second is lost more easily than the first.
2) For all practical purposes you can forget hyperplasia. Yes, it does happen, there are studies, yada, yada, yada... but it's negligible - at least for the very vast majority of people. So no increase in number of muscle fibers.
Now, there is a passive contraction of the muscles which we refer to as "tone". In two persons with the same muscle mass and the same bodyfat levels one of which exercises and the other doesn't, we are *maybe* going to feel the first person's muscles a little "harder" because exercise *may* increase that passive contraction. But this doesn't make much of a difference anyway.
There is also the age-related muscle loss that is called sarcopenia but we are not interested in that.
The normal muscle atrophy that lack of exercise brings has to do mainly with normalization of anabolic hormones. Exercise increases these hormones above normal levels. When exercise stops these hormones return to normal. E.g., your normal testosterone levels are not able to support as much muscle as your exercise-induced testosterone levels. The exact mechanisms of how various hormone levels affect muscle turnover are rather well documented. There are other atrophy mechanisms as well (metabolic, mechanical, neurological) but the hormonal ones are the most important. Those hormonal differences are responsible anyway for the vastly different muscle masses of people who have never exercised.
However, this atrophy does not affect significantly the "muscle tone" and the flabbiness of muscles that most people perceive as the effects of exercise cessation (barring the aforementioned residual muscle tone). What happens is that in most cases exercise cessation results in an increase of body fat percentage because of less energy expenditure and relaxed dietary habits. If you feel the muscles of people who are sedentary yet have very low bodyfat levels, you'll see they are rather hard despite the lack of exercise (keep in mind here that "low bodyfat levels" isn't necessarily the same as "thin" since many "thin" people don't have particularly low bf levels). If someone who stops exercise were to re-adjust his caloric intake to suit his new needs and maintain adequate protein in his diet, then his muscles would atrophy but would probably not feel any "flabbier". We also have to differentiate according to the type of exercise since a long-distance runner would probably not lose any muscle after stopping running.
That's for "muscle tone", strength is a rather different story.
1) There's sarcomere ("functional") hypertrophy (growth of the contractile components of the muscle) and sarcoplasmic ("non-functional") hypertrophy (growth of the sarcoplasm and the sarcoplasmic reticulum). The second is lost more easily than the first.
2) For all practical purposes you can forget hyperplasia. Yes, it does happen, there are studies, yada, yada, yada... but it's negligible - at least for the very vast majority of people. So no increase in number of muscle fibers.
Now, there is a passive contraction of the muscles which we refer to as "tone". In two persons with the same muscle mass and the same bodyfat levels one of which exercises and the other doesn't, we are *maybe* going to feel the first person's muscles a little "harder" because exercise *may* increase that passive contraction. But this doesn't make much of a difference anyway.
There is also the age-related muscle loss that is called sarcopenia but we are not interested in that.
The normal muscle atrophy that lack of exercise brings has to do mainly with normalization of anabolic hormones. Exercise increases these hormones above normal levels. When exercise stops these hormones return to normal. E.g., your normal testosterone levels are not able to support as much muscle as your exercise-induced testosterone levels. The exact mechanisms of how various hormone levels affect muscle turnover are rather well documented. There are other atrophy mechanisms as well (metabolic, mechanical, neurological) but the hormonal ones are the most important. Those hormonal differences are responsible anyway for the vastly different muscle masses of people who have never exercised.
However, this atrophy does not affect significantly the "muscle tone" and the flabbiness of muscles that most people perceive as the effects of exercise cessation (barring the aforementioned residual muscle tone). What happens is that in most cases exercise cessation results in an increase of body fat percentage because of less energy expenditure and relaxed dietary habits. If you feel the muscles of people who are sedentary yet have very low bodyfat levels, you'll see they are rather hard despite the lack of exercise (keep in mind here that "low bodyfat levels" isn't necessarily the same as "thin" since many "thin" people don't have particularly low bf levels). If someone who stops exercise were to re-adjust his caloric intake to suit his new needs and maintain adequate protein in his diet, then his muscles would atrophy but would probably not feel any "flabbier". We also have to differentiate according to the type of exercise since a long-distance runner would probably not lose any muscle after stopping running.
That's for "muscle tone", strength is a rather different story.
FireGarden
Philosopher
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Summary...
I've still got the same number of muscle fibres, they just got smaller individually (fewer filaments of actin and myosin in each muscle). That's because there are two processes, anabolism/catabolism, which build-up/break-down actin and myosin. Both processes are always on-going but the balance between them is changed by exercise.
And the reason I got flabby is because of the increase in fat rather than the loss of tone in muscles. This is because I carried on eating the same way I eat while exercising.
Anyway,
I'm back on the rowing machine.
It's just annoying when missing a week of exercise seems to make a big difference. I'll remember to eat less next time!
I've still got the same number of muscle fibres, they just got smaller individually (fewer filaments of actin and myosin in each muscle). That's because there are two processes, anabolism/catabolism, which build-up/break-down actin and myosin. Both processes are always on-going but the balance between them is changed by exercise.
And the reason I got flabby is because of the increase in fat rather than the loss of tone in muscles. This is because I carried on eating the same way I eat while exercising.
Anyway,
I'm back on the rowing machine.
It's just annoying when missing a week of exercise seems to make a big difference. I'll remember to eat less next time!
El Greco
Summer worshipper
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It's just annoying when missing a week of exercise seems to make a big difference. I'll remember to eat less next time!
Um... if we're talking about such a short time there may be other factors involved as well, like remission of the normal muscle inflammation that follows exercise and subcutaneous water retention (due to drinking less water and thus retaining more salt when not exercising - and also due to sweating much less). Atrophy is not a factor if we're talking for just a week. But it's still perfectly possible to gain a pound of fat in a week where you don't exercise but you eat the same - and one pound does make a difference.
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Interestingly this arcticle has just been published about how it may soon be possible to stop muscle atrophy by blocking a couple of the key genes involved. Initially it will be tested for people with severe muscle wasting diseases, but no doubt will quickly make it onto the couch potato market.
http://www.newscientist.com/channel/health/mg19125671.800-muscles-dont-use-them-dont-lose-them.html
http://www.newscientist.com/channel/health/mg19125671.800-muscles-dont-use-them-dont-lose-them.html
NeilC
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Summary...
I've still got the same number of muscle fibres, they just got smaller individually (fewer filaments of actin and myosin in each muscle). That's because there are two processes, anabolism/catabolism, which build-up/break-down actin and myosin. Both processes are always on-going but the balance between them is changed by exercise.
And the reason I got flabby is because of the increase in fat rather than the loss of tone in muscles. This is because I carried on eating the same way I eat while exercising.
Anyway,
I'm back on the rowing machine.
It's just annoying when missing a week of exercise seems to make a big difference. I'll remember to eat less next time!
Diet is the key I think. Exercise uses a depressingly small amount of calories.
They use a test called EPOC for working out how many calories are burned after exercise as opposed to merely during it. And weight training comes up nice and high on that. So not only do you use up cals doing it but burn them for free afterwards. So it's possible it's more effective than rowing/running/cycling etc for fat loss. Plus it stops muscle wastage.
FireGarden
Philosopher
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El Greco said:
Daily exercise leaves me feeling stronger than exercising every other day. But I don't notice a reduction/increase in ability.
Perhaps I've been over-reacting.
El Greco said:
So in the first week or so, the impact is mostly cosmetic/subjective?
Apart from a possible weight-gain...