Muscle lost in days, rebuilt in weeks – Knowledge

1. What this article is about

Your body constantly adjusts your muscles to demand. If it hardly needs a muscle for a few days, it breaks it down. That saves protein and energy. How fast this breakdown happens is well studied. The figures come from four very different situations: from astronauts, from healthy volunteers in the bed-rest laboratory, from a leg in a brace and from critically ill people in intensive care.

This article puts these figures side by side. It says what one week costs and how long the way back takes, with everyday activity alone and with training. It is deliberately short. The details are in three longer articles. Building muscle explains how muscle is built. Muscle strength over the years describes the course over a lifetime. Leaving hospital weaker deals with the hospital stay.

2. What one week costs

The table shows what researchers measured in different situations. All figures are averages of small groups. They describe the order of magnitude. Your own loss may be above or below them.

Three things stand out in this table.

2.1 Strength falls faster than mass

Compare the figures from the leg-brace study. After 14 days the muscle was 8 percent thinner but 23 percent weaker [3]. Strength depends on muscle mass and on how well the nervous system activates the muscle. During immobilisation both are lost. Activation is lost faster than mass. It also returns faster. That is why many people feel strong again two to four weeks after an illness, although the muscle is still thinner than before.

2.2 Two weeks with few steps are enough

The participants in the step study stayed on their feet. For two weeks they walked about 1,400 instead of 6,000 steps a day [6]. Afterwards the fat-free mass of their legs was 3.9 percent smaller. In addition, the muscle responded more weakly to protein from food. Such weeks arise with a cold, after a sprained ankle or in a month in which you hardly leave the house.

2.3 Illness makes the loss larger

The figures from the bed-rest laboratory come from healthy people who ate well. In serious illness, inflammation is added. It breaks down muscle protein further, and appetite is lacking. In intensive care, 63 critically ill people lost 17.7 percent of the front thigh muscle in ten days [7]. After seven days, 10.3 percent were already missing. Healthy young men with one leg in a brace lost 8.4 percent in 14 days [3]. Serious illness therefore cost about twice as much in ten days as two weeks of immobilisation.

3. Weightlessness: bed rest for the whole body

In weightlessness, no muscle carries the body's weight any more. For the muscles, a stay in space is therefore the same as strict bed rest. Research uses bed rest with the head end slightly lowered as a substitute for spaceflight, because it reproduces the effect of weightlessness on Earth [9].

After a Shuttle flight of eight days, crew members were missing 6 percent of their calf muscles and 10 percent of their deep back muscles [1]. After 17 days, 3 to 10 percent were missing in almost all muscle groups [10]. After flights of four to seven months on the Mir space station, 5 to 17 percent were missing [10].

On the International Space Station, nine crew members did about five hours of endurance exercise a week and strength training on three to six days [8]. Even so, in six months they lost 13 percent of calf volume and 32 percent of calf power. The researchers then called for stronger training on board. Since then, a strength device has been installed that allows squats and deadlifts with heavy loads [11]. Today the crew trains about two hours a day [12].

4. How long the way back takes

A simple rule applies to the way back: down takes days, up takes weeks.

4.1 With everyday activity alone

After a short pause, everyday activity is enough for young people. Eleven young men wore a leg brace for four days and then lived as usual for seven days [13]. After that week they had fully regained their strength. Eleven men aged 67 did the same. After the week they were still missing about 8 percent of their strength.

For longer pauses there are hardly any figures on everyday activity alone. Out of responsibility, researchers send volunteers home with a rebuilding programme after two weeks of bed rest. One finding from the bed-rest study with 67-year-olds points in one direction: after the ten days, the participants moved less of their own accord than before [5]. The everyday activity that is supposed to bring the muscle back has often itself become smaller after a pause. Anyone who relies on everyday activity alone after an illness therefore often regains only part in older age.

4.2 With training

Nine men between 61 and 74 and eleven men between 21 and 27 wore a leg brace for two weeks [14]. They then did four weeks of supervised strength training. Both groups had regained their maximal strength after the four weeks. The young men had also regained their muscle mass and power. The older men were still missing part of both. Four weeks were too short for them.

The type of training matters too. In a second study, 17 young and 15 older men cycled for six weeks after two weeks in a brace [15]. Muscle mass came back, strength only partly. Anyone who has lost strength must train strength.

4.3 A rule of thumb

One week of strict bed rest costs a young person about 3 percent of thigh cross-section [2]. During rebuilding, the cross-section grows initially by about 0.1 to 0.2 percent per training day [16]. With three sessions a week, the way back for these 3 percent therefore takes four to eight weeks. As a rule of thumb: one day in bed costs what about five days of training bring back. The figure is rough and applies to healthy young people. In older age the way back takes longer.

Astronauts need this way back too. After six months on the space station, a programme with physiotherapy follows [12]. One crew member had regained all measured values after 21 days of this programme, except jumping power. That took longer.

5. What you can do

The following points are based on the bed-rest studies and on the experience of specialists [17]. According to our search, there are no studies that compared different approaches to a flu at home.

• As long as you have a fever, rest is right. As soon as it is gone, every day counts.
• Sitting loads the legs more than lying, standing more than sitting. In your sickbed or on the sofa, stand up once every hour.
• Several times a day, stand up from a chair five to ten times, without using your hands if you can. That is strength training.
• Eat protein with every meal, even without appetite: an egg, quark, pulses, fish or meat [17].
• If an arm or a leg is immobilised, keep training the other side and the trunk. The cast affects one part of the body, the loss otherwise the whole body.
• Rebuild early after the pause, with strength training. Keep going longer than feels necessary. Feeling strong again after two weeks is activation. The muscle itself needs two to three months. Talk to us if you would like a programme.

6. What you should know

• One week of strict bed rest costs young men about 3 percent of thigh cross-section and 7 percent of leg strength [2]. At 67, ten days cost about one kilogram of leg muscle and 13 percent of knee extensor strength [4], [5].
• Strength falls faster than mass [3]. Activation returns in weeks, mass in months.
• Two weeks with few steps are enough for a loss, with no bed involved [6].
• Serious illness costs about twice as much in ten days as two weeks of immobilisation [3], [7].
• Weightlessness acts like bed rest [9]. Six months on the space station cost 13 percent of calf volume and 32 percent of power despite on-board training [8].
• With everyday activity alone, only part comes back in older age [13]. With strength training, strength returns in four weeks; mass and power take longer in older age [14].
• One day in bed costs what about five days of training bring back [2], [16]. The figure is rough.
• Stand up every hour, rise from a chair, protein with every meal, keep training the healthy side [17].

References

All Digital Object Identifiers (DOI) were checked against the Crossref register. The links in the reference list lead via the DOI service to the publishers' pages, and for one paper without a DOI to the PubMed database. Some of these are located outside Switzerland and the EU. When you click, your IP address is transmitted to the respective provider. This does not happen on our site itself.

[1] LeBlanc A, Rowe R, Schneider V, Evans H, Hedrick T. Regional muscle loss after short duration spaceflight. Aviation, Space, and Environmental Medicine. 1995;66(12):1151–1154. PMID 8747608

[2] Dirks ML, Wall BT, van de Valk B, et al. One Week of Bed Rest Leads to Substantial Muscle Atrophy and Induces Whole-Body Insulin Resistance in the Absence of Skeletal Muscle Lipid Accumulation. Diabetes. 2016;65(10):2862–2875. https://doi.org/10.2337/db15-1661

[3] Wall BT, Dirks ML, Snijders T, Senden JM, Dolmans J, van Loon LJ. Substantial skeletal muscle loss occurs during only 5 days of disuse. Acta Physiologica. 2014;210(3):600–611. https://doi.org/10.1111/apha.12190

[4] Kortebein P, Ferrando A, Lombeida J, Wolfe R, Evans WJ. Effect of 10 days of bed rest on skeletal muscle in healthy older adults. JAMA. 2007;297(16):1772–1774. https://doi.org/10.1001/jama.297.16.1772-b

[5] Kortebein P, Symons TB, Ferrando A, et al. Functional impact of 10 days of bed rest in healthy older adults. The Journals of Gerontology Series A. 2008;63(10):1076–1081. https://doi.org/10.1093/gerona/63.10.1076

[6] Breen L, Stokes KA, Churchward-Venne TA, et al. Two weeks of reduced activity decreases leg lean mass and induces «anabolic resistance» of myofibrillar protein synthesis in healthy elderly. The Journal of Clinical Endocrinology & Metabolism. 2013;98(6):2604–2612. https://doi.org/10.1210/jc.2013-1502

[7] Puthucheary ZA, Rawal J, McPhail M, et al. Acute Skeletal Muscle Wasting in Critical Illness. JAMA. 2013;310(15):1591–1600. https://doi.org/10.1001/jama.2013.278481

[8] Trappe S, Costill D, Gallagher P, et al. Exercise in space: human skeletal muscle after 6 months aboard the International Space Station. Journal of Applied Physiology. 2009;106(4):1159–1168. https://doi.org/10.1152/japplphysiol.91578.2008

[9] Hargens AR, Vico L. Long-duration bed rest as an analog to microgravity. Journal of Applied Physiology. 2016;120(8):891–903. https://doi.org/10.1152/japplphysiol.00935.2015

[10] LeBlanc A, Lin C, Shackelford L, et al. Muscle volume, MRI relaxation times (T2), and body composition after spaceflight. Journal of Applied Physiology. 2000;89(6):2158–2164. https://doi.org/10.1152/jappl.2000.89.6.2158

[11] Juhl OJ, Buettmann EG, Friedman MA, DeNapoli RC, Hoppock GA, Donahue HJ. Update on the effects of microgravity on the musculoskeletal system. npj Microgravity. 2021;7:28. https://doi.org/10.1038/s41526-021-00158-4

[12] Petersen N, Lambrecht G, Scott J, Hirsch N, Stokes M, Mester J. Postflight reconditioning for European Astronauts – A case report of recovery after six months in space. Musculoskeletal Science and Practice. 2017;27(Suppl 1):S23–S31. https://doi.org/10.1016/j.msksp.2016.12.010

[13] Hvid LG, Suetta C, Nielsen JH, et al. Aging impairs the recovery in mechanical muscle function following 4 days of disuse. Experimental Gerontology. 2014;52:1–8. https://doi.org/10.1016/j.exger.2014.01.012

[14] Suetta C, Hvid LG, Justesen L, et al. Effects of aging on human skeletal muscle after immobilization and retraining. Journal of Applied Physiology. 2009;107(4):1172–1180. https://doi.org/10.1152/japplphysiol.00073.2009

[15] Vigelsø A, Gram M, Wiuff C, Andersen JL, Helge JW, Dela F. Six weeks' aerobic retraining after two weeks' immobilization restores leg lean mass and aerobic capacity but does not fully rehabilitate leg strength in young and older men. Journal of Rehabilitation Medicine. 2015;47(6):552–560. https://doi.org/10.2340/16501977-1961

[16] Wernbom M, Augustsson J, Thomeé R. The Influence of Frequency, Intensity, Volume and Mode of Strength Training on Whole Muscle Cross-Sectional Area in Humans. Sports Medicine. 2007;37(3):225–264. https://doi.org/10.2165/00007256-200737030-00004

[17] English KL, Paddon-Jones D. Protecting muscle mass and function in older adults during bed rest. Current Opinion in Clinical Nutrition and Metabolic Care. 2010;13(1):34–39. https://doi.org/10.1097/MCO.0b013e328333aa66

Transparency

• Authorship: Roger Hilfiker
• AI assistance: the literature search and the draft text were produced with Claude (Anthropic). Roger Hilfiker checked all statements, figures and sources and revised the text.
• Created: 5 September 2026
• Last updated: 5 September 2026
• Sources: the 17 papers in the reference list. All DOIs were checked against the Crossref register.
• How the sources were found: searches of the Europe PMC and Crossref databases in September 2026 on muscle loss during bed rest, immobilisation, reduced step counts, critical illness and spaceflight, and on recovery afterwards with and without training. Where this article says that no study exists on a question, this refers to that search.
• Conflict of interest: our practice offers rebuilding programmes after illness and surgery and earns from the treatment. This article says that the figures come from small groups of healthy men and that there are hardly any studies on recovery with everyday activity alone over longer periods.
• Funding: Physiotherapie Tschopp & Hilfiker, 3902 Glis. The article was produced from the practice's own resources.
• Next review: 5 September 2028.