Whether it is a cold, a fall or an operation, when an older person is in bed or in hospital for a few days, carers often notice that the person has become weak all over, has difficulty standing and walks more slowly. This is not an illusion. It is disuse atrophy: once muscle loses its daily load, it is lost at an astonishing speed, and the loss in older people is worse than in young people. The article on the causes and diagnosis of sarcopenia already lists bed rest as one of the secondary causes. This article goes deeper into another core question: how fast the loss is, the mechanism behind it, how a hospital stay sets off a “downward spiral”, and how the lost muscle can be regained.
First, the nature of the evidence should be made clear. The core loss rates quoted below come from a mechanistic controlled bed rest study of only 12 people, so the values are all given as approximate. In addition, complete bed rest in an experiment is not the same as an ordinary hospital stay, and the actual size of loss depends on the degree of bed rest, usually lying between the two. The overall trend is clear, but the size differs from person to person. For the overall concept, see the overview of physiotherapy for sarcopenia.
How fast muscle is lost in ten days of bed rest
Kortebein and colleagues (2007, JAMA) recruited 12 healthy older adults who were moderately active in daily life (average age about 67, half men and half women). With a diet matched for energy and the basic recommended protein intake, they were put on complete bed rest for 10 days. In those ten days, the body paid the price below.
Two points are worth noting here. First, the muscle loss is concentrated in the legs. The leg muscles that work against gravity are the first to be unloaded once they stop bearing weight. Second, this loss does not come from a “surge in breakdown”. It comes from “synthesis stopping work” (the mechanism is explained below). For an older person who already has to make an effort to stand and walk, losing nearly a kilogram of muscle from the legs is enough to take them from “able to walk about unaided” to “needing someone to support them”.
Muscle loss in older people after ten days of bed rest compared with young people after twenty-eight days
What carers most need to be alert to is the amplifying effect of age. The same series of research and a later literature review (English & Paddon-Jones 2010) point out that the leg lean mass lost by older people after 10 days of bed rest (about 0.95 kg) is already more than the loss in young people (average age about 38) after 28 days of bed rest (less than 0.4 kg from the legs). In other words, “a few more days lying down” is no small matter for an older person. For the same time in bed, the muscle cost to the older person is several times that of a young person.
Important note: the statement that “older people lose more in 10 days of bed rest than young people in 28 days” is a comparison across studies and different samples, and not a direct comparison from a single randomised trial. The direction that older age speeds up disuse muscle loss is clear, but how many times different it is will still vary with individual constitution and the degree of bed rest. All the loss rates listed on this page are approximate values from small mechanistic studies, and should not be taken as precise figures that predict what happens to every older person.
Three mechanisms by which bed rest causes rapid muscle loss
To understand “how to regain muscle mass”, it is first necessary to understand “why it is lost”. In the muscle atrophy caused by disuse, the key is not that muscle is “broken down” faster. It is that the side that builds it has stopped work.
The main cause of muscle loss is reduced protein synthesis
- The amount of muscle in the body depends on the balance between muscle protein synthesis (MPS) and breakdown (MPB). When muscle is not used, this balance turns negative, mainly because the synthesis process that makes muscle is suppressed (Nunes 2022).
- The driving factor is reduced mechanical load. With no work to do, the muscle stops building, so restoring load early is the key to reversing it.
The legs lose the most, and older people respond more sluggishly
- The muscles of the legs normally work against gravity. Once the person is in bed and no longer stands up or walks, this group of muscles loses mass fastest and by the largest amount. This is why, in Kortebein's study, nearly two thirds of the muscle loss was in the legs.
- Older people also have anabolic resistance: with the same load and nutrition, older people respond more slowly in rebuilding muscle (Nunes 2022, English 2010), so disuse hits older people harder and recovery takes longer.
How an acute hospital stay sets off continuing decline in fitness
The muscle loss caused by bed rest is not a single event. It sets off a cycle that keeps getting worse. As muscle is lost, the older person feels weak. The weaker the person feels, the less willing they are to move, and the more likely they are to be kept in bed. As activity falls, muscle loss gets worse, and activities of daily living (ADL) go backwards with it. Once bodily function declines, it is even harder to start moving again. This is the downward spiral commonly seen in older inpatients. Other factors during a hospital stay can make the loss worse, but those are for the treating doctor to handle. What rehabilitation can cut is exactly this vicious circle of “bed rest, weakness and less activity”.
- 1Muscle lossLong bed rest means the legs are not loaded, and the strength and muscle mass of the legs fall sharply.
- 2Function declinesThe ability to stand, walk and balance gets worse, and the person tires more easily and falls more easily.
- 3Activity falls furtherFeeling weak and worried about falling, the person moves less, and may even have to stay in bed.
- 4Disability deepensSelf-care ability (ADL) declines, which brings the person back to the start of muscle loss, and the situation gets worse.
This vicious circle is supported by evidence, and the older the person, the more serious it is.
Being clear about cause and effect: the studies by Covinsky and Zisberg are both observational studies. They show that two things are linked, and not a direct “cause and effect”. Zisberg points out clearly, though, that the amount of activity during the hospital stay is a modifiable factor, which means we can step in actively to improve it.
Steps and principles for getting out of bed early
Since the amount of activity is a modifiable factor, the direction of response is quite clear: as long as the illness allows, the older person should be helped to move again as early as possible, and not just left to “rest in bed”. The steps for letting muscles take load again can be arranged roughly from low to high intensity as follows.
- Assess before starting: a physiotherapist assesses the older person's mobility according to the illness, body measures and fall risk, and sets the intensity at which training starts.
- Begin by sitting up: first try sitting up in bed or at the bedside, so that the body gets used to sitting upright again and the circulation is trained to tolerate it.
- Getting out of bed and short walks: take the first steps with someone holding on or with a walking frame, and then increase the walking distance step by step.
- Simple resistance movements at the bedside: simple movements such as sit-to-stand practice, pumping the ankles up and down (ankle pump exercise) or pulling a resistance band put load back on the legs and stop the rate of muscle synthesis from falling further.
- Never push on alone or at the risk of falling: the specific intensity and progression of training differ from person to person and must be assessed by a therapist and graded accordingly (a consensus in practice).
Regaining muscle mass: resistance training together with nutrition
The last and most important question is whether the muscle that has been lost can be regained. It can be regained, but there must be active intervention, and recovery is much slower than loss. After disuse, muscle recovery in older people is often slower and may never be complete (English 2010, Nunes 2022). Muscle never “recovers slowly by itself”, and if nothing is done, a single episode of loss builds up into long-term sarcopenia.
The response with the most evidence is resistance training. McKendry and colleagues (2024) state clearly that the disuse brought on by bed rest, illness, limb immobilisation or hospital stay makes sarcopenia worsen faster, briefly but significantly. Resistance training strongly stimulates muscle protein synthesis, and whether done before, during or after bed rest, it helps to reduce muscle loss and speed recovery, with better results when there is enough dietary protein. For older people who are frail or have just left hospital, resistance training at home needs professional screening and supervision, and this is exactly the value of home physiotherapy.
The core method for regaining lost muscle is resistance training together with enough protein. To learn about the specific amount of training, the movements and how to progress step by step, see the topic page on resistance training for sarcopenia (the core treatment for rebuilding muscle strength). For how protein works together with training, see the material on nutrition and protein for sarcopenia. If you would like a first idea by measuring calf circumference and doing a sit-to-stand test at home, that article is also worth reading (though a self-test is only a first screening and not a formal diagnosis).