IMMOBILIZATION INITIATES ANABOLIC RESISTANCE IN YOUNG MEN
For the purposes of understanding not only the importance of, but the association between, physical inactivity & lean body tissue, this might be one of the more pertinent abstracts I've come across in a while.
Studies such as this one, from the American Journal of Physiology, delve into several of the mechanisms potentially involved in the initiation of disuse atrophy at the cellular level, but I found the original link - also published in the American Journal of Physiology - to be a swift crystallizing kick in butt, highlighting just how brutally fast evolution can do the job of eliminating useless tissue for the purpose of energy conservation.
It's fairly well established that complete disuse can lead to a somewhat rapid loss of lean body mass. We've all seen it before, a friend breaks their wrist, has it placed in a cast for several weeks, then, as the cast is removed, a withered, tiny, pasty forearm is revealed. Given that the process of bone repair tends to last several weeks or months, our visual experience of the muscle atrophy associated with bone repair is skewed because the muscle is hidden by the cast, and we assume it takes the same several weeks or months for muscular atrophy to occur as well.
We couldn't be more wrong. Researchers have now shown that disuse atrophy and anabolic resistance both occur as early as 5 days after complete immobilization. The best part, is that it occurs in young men, at the age of 22.
If you take a 22 year old male - with his naturally occurring anabolic hormones and potential for muscle growth - and you immobilize his leg in a cast for 5 days, he will lose approximately 4% of total muscle size, and his rate of protein synthesis - muscle building - even while continuously being fed 25 grams of amino acids, will diminish in the realm of 41% - 53%.
Needless to say this is quite substantial. The authors note that "short, successive periods of muscle disuse throughout the lifespan play an important role in the development of sarcopenia."
For me, the take-away is that prolonged periods of very low activity or inactivity - even absent complete immobilization - will assuredly lead to muscle wasting and anabolic resistance as times goes by.
The information in that abstract should be used as a weapon of self-defense. It's as good a call to action as I've ever seen, and it points the needle of effort squarely in the direction of 'get active, and get as strong as you can, before it's too late'. The last thing anybody wants, is to be tangled up in the Diseasome of Physical Inactivity, well before their time.