Muscles stay alive if they can receive the right amount of energy and they are allowed to work–if any or neither of the two conditions is fulfilled, muscle loss becomes inevitable. In answer to how long it takes to lose muscle mass, it depends on numerous factors–here are the most important ones:
Level of Fitness
Paradoxically, the fitter you are, the sooner you start losing muscle mass if you stop training. Professional athletes start experiencing muscle atrophy after a little more than two weeks, while people who work out only for recreational purposes don’t experience muscle loss for around three months of inactivity.
Type of Work-out
The type of exercise pursued before becoming inactive is also a factor that determines the period for which the body maintains muscle mass without training. Endurance exercise makes slow-twitch muscles contract harder, a process that generates leaner muscles, while the exercises done by power lifters cause fast-twitch muscle fibers to work harder, thus building muscle mass. Slow-twitch fibers tend to atrophy at a slower rate, that’s why those engaged in endurance training are likely to be able to preserve their muscle mass for around twelve weeks, while weightlifters start losing muscle in after around two weeks of inactivity.
The body’s natural aging process involves a process called sarcopenia, during which muscle loss accelerates while the amount of fat inside the muscle increases. The body starts losing 3-5 percent of its muscle per ten years and muscle loss becomes faster and the atrophy is more intensive with age, that’s why elderly people find it more difficult to rebuild lost muscles.
We list gender here only to say that gender does not seem to be related to the rate of muscle loss during inactive periods–the male and the female body seems to react the same way to inactivity in terms of the preservation or loss of muscle mass.
Other Factors that Influence the Pace of Muscle Loss
The list of factors that determine the pace of muscle loss during longer inactive periods cannot possibly be complete without including the usual suspects: stress and insufficient sleep. Stress is known to upset the body’s hormonal balance and it reduces the level of anabolic hormones such as anabolic steroids including testosterone that promote muscle growth and it increases the level of catabolic hormones such as cortisol and adrenaline that inhibit muscle growth.
Lack of sleep also affects the body’s ability to grow new muscles, while prolonged insomnia or negative changes in the quality of sleep also promote insulin resistance and muscle loss, that is why the treatment of sleep disorders is one of the most modern approaches to the prevention of muscle loss in the case of elderly patients.
It is not all bad news, though. Muscle loss does not seem to start to lose muscle mass very soon after ceasing to exercise regularly, but a one-week resting period introduced two times a year is considered to be highly beneficial and those two weeks spent away from the gym will not cause any visible harm to your muscle mass. So, if you train regularly and you want to relax a bit, don’t worry - you will only return to your gym stronger and more motivated after the break!