In healthy older adults, just 10 consecutive days in bed lowers isotonic knee extensor strength by an average of about 13% (Kortebein 2008), and the participants in that study had an average age of only 67. These figures are surprising because the participants were not ill and not frail. Doing nothing for ten days was enough for strength to drain away at a speed the eye cannot see. Clinically, this acute loss of function caused by lack of activity is called deconditioning.
Deconditioning is measured in days. In healthy older adults, 10 consecutive days in bed lowers knee extensor strength by about 13% (Kortebein 2008), and about one in three hospitalised older people leave hospital with worse ability in activities of daily living (ADL) than on admission (Loyd 2020; Covinsky 2003 gives 35%). This comes from a fall in muscle protein synthesis and not simply from too little rest. This page concentrates on three core questions about the decline itself: what happens when the body does not move, how fast, and how it is measured. Why the decline can be reversed, how many stages rehabilitation training has and which complications long bed rest brings are outside the scope of this page.
Deconditioning and hospitalisation-associated disability (HAD): differences and relationship
Two medical terms that are often used interchangeably need to be separated first. Deconditioning describes the physiological mechanism: the body loses strength, cardiorespiratory endurance and bone mass because of lack of activity. Hospitalisation-associated disability (HAD) describes the clinical consequence: after a hospital stay, an older person has lost some ability to look after himself or herself in daily life. The first is the cause and the second the result, and the two are closely linked during a hospital stay.
| Deconditioning | This is acute physiological decline caused by lack of activity (such as bed rest, prolonged sitting or hospitalisation), in which strength, cardiorespiratory endurance and bone density all fall together. It is a process or mechanism inside the body and can occur independently of the original illness. |
| Hospitalisation-associated disability (HAD) | This means that when an older person leaves hospital, some daily ability (such as going to the toilet alone, bathing or walking) has been lost compared with the baseline before admission. It is the actual functional result. According to the meta-analysis by Loyd (2020), the pooled proportion of older people admitted acutely who have this is about 30% (95% confidence interval 24 to 33%). |
| How the two relate | Among the many causes of HAD, deconditioning is the one most open to prevention. It develops as follows: lack of activity lowers strength, which makes transfers and walking worse, and finally self-care is lost. Starting activity early can stop both problems from occurring. |
How lack of activity affects muscle, bone and the cardiorespiratory system
Lying in bed does not simply let the muscles rest. It switches off the signals that maintain several systems in the body at once. The review by Parry and Puthucheary (2015) shows that within the first week of prolonged bed rest, muscle mass, bone density and other physiological systems already fall quickly, and that the decline is greater still in a critical illness setting. In older people the muscle loss is driven mainly by a slowing of protein synthesis. In other words, the body stops making new muscle, and it is not simply that the muscle is used less.
Less muscle protein synthesis
- Bed rest lowers the synthesis of muscle protein and makes the muscle fibres thinner
- The antigravity muscles that hold posture, such as those of the thighs, buttocks and calves, are affected first
- In an older person, 10 consecutive days in bed lose about 0.95 kg of lean leg mass (Kortebein 2007)
Decline in bone and cardiorespiratory function
- When bone loses the stimulus of bearing weight, bone density begins to fall in the first week in bed (Parry 2015)
- Cardiorespiratory endurance, plasma volume and the ability to regulate blood pressure on changing posture all fall together
- This makes the older person dizzy on standing and breathless after a few steps, so that out of fear the person avoids activity, which sets up a vicious circle
It is worth noting that this acute loss partly overlaps in physiology with the long-term decline of age-related sarcopenia, but the speed and trigger of the two are quite different. Sarcopenia is a chronic decline over many years, whereas deconditioning can pile on quickly during a single hospital stay, so that an older person who was already frail loses function more sharply.
How fast muscle is lost in bed
The point on which deconditioning most defies common intuition is the time scale, which is not months or years but days. Several controlled trials agree that muscle shrinks clearly within the first one or two weeks in hospital. In healthy older adults, 10 days in bed lowered knee extensor strength by about 13% (Kortebein 2008), and in critically ill patients the muscle loss comes even earlier and faster. This explains why families so often sigh that the older person could walk about freely on admission but is like a different person on coming home. To a large extent this is not the original illness getting worse but the price of not moving in bed.
The loss is not spread evenly over each day. It is sharpest in the first few days and then builds up day by day with the days in bed. The day-by-day curve of muscle and lean mass loss, and the comparison of loss rates between groups (healthy older adults compared with critically ill patients), are set out in the day-by-day timeline of muscle loss in bed.
Why older people lose muscle faster
With the same time in bed, older people lose far more muscle than young people. Kortebein (2007) found that older adults lose more lean leg mass in 10 days in bed than young people do in 28 days. The main reason is that the ability of older people to synthesise muscle protein is already reduced, so when activity stops it is even harder for the body to maintain muscle mass. Older people also usually have a smaller muscle reserve to begin with, so even the same percentage loss has a more serious effect on real daily function, such as whether the person can stand up from a chair alone.
In other words, an older person faces the double disadvantage of losing quickly and having little in reserve. It also explains why, in research on critical illness (Puthucheary 2013), the more severe the illness and the more organs have failed, the earlier and more sharply the muscle shrinks, because the body, in dealing with acute illness, draws further on resources that would otherwise be used to maintain muscle. Once it is understood that muscle loss is an active and accelerated process and not just passive wearing down, it is clear why clinicians keep stressing that the sooner the patient is out of bed, the better, and do not wait until the illness has completely recovered to start activity.
Proportion of older people with a fall in daily ADL at discharge
Translating the physiological loss of muscle into the consequences of real life brings us to the loss of self-care ability. Covinsky (2003) followed 2,293 people aged 70 and over admitted to hospital with medical illness and found that about 35% had worse ADL function at discharge than their baseline before admission, with the fall increasing with age. The meta-analysis by Loyd (2020) further puts the pooled proportion across studies at about 30%.
The gap between age groups deserves particular attention. About 23% of the 70 to 74 age group had a fall in function, but in the group aged 90 and over the proportion rose sharply to 63%. This means that the same hospital stay hits the older patient harder, and recovery after discharge is also harder. This is why the key window for rehabilitation in the first few weeks after discharge must be used.
Three bedside tools physiotherapists use to assess physical decline
To judge accurately whether an older person has deconditioning, it is not enough to see that the person looks thinner. Muscle strength and physical function must be quantified objectively. Physiotherapists often use three low-cost tools that can be used at the bedside and have clinical evidence behind them, to assess lower limb strength, overall muscle status and overall fitness:
| 30-second sit-to-stand | This test counts how many times the person can go from sitting to standing in 30 seconds and is a direct reflection of lower limb strength. Its results correlate with maximal leg-press strength at r=0.78 (men) and 0.71 (women), so it is both reliable and suited to the bedside (Jones 1999). |
| Grip strength (handgrip) | Grip is measured with a handheld dynamometer and serves as a simple indicator of overall muscle status. A low grip strength can be used to predict mortality risk, length of hospital stay and decline in physical function (Bohannon 2015). |
| SPPB | This is a combined score of three tests: standing balance, 8-foot walking speed and five sit-to-stands. In a study of more than 5,000 people aged 71 and over, the score was confirmed to predict the risk of disability, death and admission to a care home (Guralnik 1994), and it is well suited to following changes in physical function before and after a hospital stay. |
The core value of these assessment tools lies not in a single number but in the comparison before and after. By comparing the number of sit-to-stands or the walking speed measured after discharge with the older person’s function before admission, the part of the fall that is deconditioning and can be won back by rehabilitation training can be estimated. Once decline is confirmed, how to train step by step is set out in the graded programmes of progressive rehabilitation training after bed rest.
Signs of physical decline that can be seen at home
In Hong Kong, deconditioning most often shows itself in two home situations. In the first, an older person living in public housing returns home from hospital. Before admission the person could go to the toilet alone, but after two weeks in hospital even standing up from the edge of the bed needs a hand on the cabinet for support, and walking to the toilet needs the family to hold on. This is typical lower limb deconditioning after bed rest. In the second, an older person living alone dares not get out of bed for fear of falling after discharge and sits on the sofa watching television all day. The family often mistakenly think that more rest is perfectly normal, when the reality is that it speeds up the vicious circle of moving less and getting weaker, and getting weaker and being more afraid to move.
At home assessments, the most common thing heard from the family is that the older person could move about freely before admission but is completely different after coming home. The family often put this down to the illness not having fully recovered and overlook the effect of bed rest itself. The first step in assessment is therefore to tell whether the physical decline comes from the original illness or from disuse caused by bed rest. Measuring the 30-second sit-to-stand count and walking speed, and comparing them with function before admission, shows how much is the reversible disuse component. At home, the earliest warning is usually not muscle visibly getting thinner but transfers clearly getting slower, such as going from the bed to a chair or from sitting to standing needing both hands or several attempts. This change in sit-to-stand ability often shows deconditioning faster than the visible muscle mass does, and it is also a key indicator that directly affects safety at home and the risk of falls.
Three kinds of signs the family can look out for at home:
- Slower transfers—When the older person goes from the bed to a chair or from sitting to standing, both hands are needed on the armrests, or several attempts are needed before the person gets up. This is the earliest sign of functional decline and the one that best reflects the safety risk of falls.
- Lower walking speed—The older person is clearly slower going to the toilet or the living room than before the hospital stay, and needs someone to hold on or a wall to lean on on the way. This reflects that lower limb strength and balance are declining together.
- Weak grip—The older person finds it hard to twist off a bottle cap, wring out a towel or turn a door handle in daily life, which is also a simple sign that overall muscle status has fallen.
These signs at home cannot replace a professional clinical assessment, but they help the family notice something wrong early and look for help. If an older person is clearly weaker after discharge, the home physiotherapy provided by Nova Health’s registered physiotherapists uses the 30-second sit-to-stand, grip strength and SPPB to measure the older person’s functional performance objectively, and compares it with the baseline before admission, to define the reversible disuse component and draw up targeted rehabilitation training.
On community support, for older people who need to continue daily care and rehabilitation training at home, the Social Welfare Department offers the 體弱長者家居照顧服務 (called Integrated Home Care Services (Frail Cases) until 1 April 2026), whose scope covers nursing, rehabilitation exercise and personal care. The service is referred through the Standardised Care Need Assessment Mechanism for Elderly Services, and the family can apply through the medical social services unit of the hospital, or through the nearest District Elderly Community Centre, Neighbourhood Elderly Centre or home care service team. For a fuller plan of rehabilitation after bed rest, see the overview of rehabilitation after a long hospital stay.