Introduction

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Sometimes life happens and we are unable to train for one or two weeks. Other times, we become injured or sick so that we take extended breaks from training. If this has happened to you, it’s inevitable that you start to wonder when you will lose your progress. Some people start to worry after two days, while others worry after two weeks. In this article, I will answer how detraining affects strength, muscle size, and endurance.

 

When do you lose strength?

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Strength Loss in Beginners

In beginners, it seems like strength is lowered after 3 weeks of detraining, but in the long-term it doesn’t seem to make much difference. Three studies find that you can take 3 weeks off of training without fear of losing strength (Häkkinen et al., 2000; Ogasawara et al., 2011; Ogasawara et al., 2013). One study finds a small decrease in estimated 1RM after 4 weeks of detraining (Ochi et al., 2018).

The figure shows how 1RM changes over the course of 24 weeks of training. The black lines (PTR group) trained for 6 weeks, then took a break for 3 weeks (rinse and repeat). The white line (CTR group) trained continuously. By the end there was little difference in maximum strength between groups. Figure by Ogasawara et al. (2013).

A study by Costa et al. (2016) found that 1RM leg extension strength remained high above baseline during 2 weeks of detraining. The interesting twist here is that the participants only trained their leg one week (3 sessions) before detraining. So they barely got one good week of training done. And still the strength is almost unchanged two weeks later:

Figure by Costa et al., 2016

The figures above raise some questions:

• Is more better? (Not necessarily, as per our review on overtraining from 2016)
• What is ideal periodization for beginners?
• Doesn’t volume matter as much for beginners?

At this point in time, I won’t speculate and try to answer these questions, but I do think the data is very interesting. I will write an in-depth review on periodization in the future (I have 60+ studies on this topic!).

Strength Loss in Trained Lifters

There is much more data on trained lifters. For this section I will mainly cite one systematic review by McMaster et al., (2013). The review analyses 27 studies to determine what the ideal frequency, volume, etc. for strength gains in rugby players. They also examine detraining and how it affects strength. The participants had the following characteristics:

“‘Highly trained’ athletes are those whom have been resistance training for 3 plus years and are currently participating in collegiate level, state level, semi-professional and professional sport [37]. Studies utilizing these elite athletic populations were included in this review, all others were excluded.”

So we are talking about trained athletes. Here’s what they found regarding detraining and strength:

"Based on the above outcomes and past literature, [ 9, 10, 12, 17, 29, 42, 58, 60, 63, 84] it can be speculated that maximum strength levels can be maintained for up to 3 weeks without resistance training, but decay rates will increase thereafter (5–16 weeks).”

This is the best evidence we have for now when it comes to trained lifters and detraining. The conclusion is also supported by another review which concludes:

“Strength performance in general is (...) readily retained for up to 4 wk of inactivity, but highly trained athletes’ eccentric force and sport-specific power may suffer significant declines.” (Mujika and Padilla, 2001).

Update: A study from 2017 finds that trained men retain strength and muscle mass during a 2 week period of detraining (Hwang et al., 2017)

 

When do You Lose Muscle Mass?

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Muscle Atrophy in Beginners

Some studies suggest that muscles start to atrophy within 2 weeks of detraining (Hortobágyi et al., 1993; Jespersen et al., 2011; McMahon et al., 2014; Dirks et al., 2016) or 3-6 weeks (Ochi et al., 2018). Yet, the answer it isn’t that straightforward.

The main issue is that muscle glycogen is also lost very quickly when we stop exercising (Costill et al., 1985; LaForgia et al., 1999; Mujika and Padilla, 2000; Mujika and Padilla, 2001). And when glycogen stores shrink, it affects our perceived muscle size.

Glycogen depletion following 4 weeks of detraining in competitive swimmers (Costill et al., 1985)

When researchers measure gains, they will look at things like Fat-Free Mass (FFM), Lean Body Mass (LBM), or Fiber Cross Sectional Area (CSA). They will do this by using tools like DXA, BIA, MRI, or muscle biopsy. Now, these measurements are useful, but they are also affected by how much glycogen we store in our muscles (Bone et al., 2016). So when muscle glycogen stores shrink during detraining, we “lose” muscle mass, or more accurately, the water contents of our muscles decreases (Nygren et al., 2001).

On the flipside, you could even "trick" body estimates by going on a high carb diet to glycogen load your muscles (Rouillier et al., 2015; Bone et al., 2016). On the flipside, going low-carb or on a cut can lower your glycogen and water stores. This affects "muscle mass" (Hulmi et al., 2016)

This is why we have to take the atrophy and hypertrophy studies with a grain of salt. When beginners start exercising, their muscle glycogen stores will grow quickly and they will retain more water, as shown below:

What 16 weeks of strength training does for total body water in beginners.
Figure by Ribero et al., 2014

If researchers were to measure gains after a couple weeks of training, it could simply be increased muscle glycogen. On the other hand, if researchers are using tools that can detect water changes within our bodies, then they can measure “real” muscle protein gains much better (LaForgia et al., 1999; Mallinson et al., 2011). Indeed, a study found that endurance athletes lost muscle mass during a 3-week detraining period (LaForgia et al., 1999). However, the muscle mass loss was only found using measurement tools that weren’t ideal for the job (2 and 3 compartment models). Check out a comparison of the models below:

Figure by Mallinson et al., 2011

Luckily, the same researchers also measured water mass using a 4 compartment model. They found that the 0.7 kg loss of lean mass was actually a loss of 0.7 kg total body water. Hence, the detrained athletes didn’t lose any muscle mass during a three week break from training (LaForgia et al., 1999). But, their muscle glycogen stores did shrink.

However, let’s assume that 2-3 weeks detraining in beginners leads to muscle loss. Does it matter in the long-term? Studies by Ogasawara et al., 2011 and Ogasawara et al., 2013 suggest that it makes little difference:

The figure shows how CSA [hypertrophy] changes over the course of 24 weeks of training. The black lines (PTR group) trained for 6 weeks, then took a break for 3 weeks (rinse and repeat). The white line (CTR group) trained continuously. By the end there was little change in gains. Note that the CTR group did a lot more volume because they never took a break: “the PTR group had 25 % fewer training sessions”. Figure by Ogasawara et al., 2013.

My bet is that muscle glycogen stores shrunk during the detraining phases, and rebounded during the training phases. Therefore, we are, to some extent, observing changes in muscle glycogen, not muscle mass. Though I don’t know exactly how much of the gains are glycogen gains compared to “dry” muscle protein gains (the researchers didn’t control for body water). As you can see, the continuous group (CTR) made huge gains the first 6-9 weeks of training and then the curve becomes much flatter. I think this is because they made both muscle protein gains and glycogen gains. Once the "wet" glycogen/water gains wear off, we are left with dry gains.

Though I will write a counterpoint: Muscles can contain a maximum of 4g glycogen per 100g wet muscle (Hansen, 1999). Glycogen can bind 3g of water per gram (Ribero et al., 2014). So the maximum amount of glycogen + its bound water is:
4g + 4*3g
= 4g + 12g
= 16g (per 100g muscle).

The final answer is 16% (shoutout to Greg Nuckols for writing about this 2015). This shows us that glycogen and its bound water can’t make up huge changes in gains. But, it would explain small changes in muscle mass during detraining (for example a loss of 5-6% CSA as some studies have suggested (Hortobágyi et al., 1993; Ogasawara et al., 2013). When it comes to filling muscles with glycogen, one study found that glycogen loading lead to a 3,5% CSA increase in untrained people (Nygren et al., 2001) while another study detected a 2-3% FFM increase in well-trained cyclists (Bone et al., 2016). Perhaps glycogen loading/depletion plays an even bigger “hypertrophic” role in people who have at least 10-16 weeks of resistance training experience?

Glycogen reduction following detraining would also explain, along with other factors, why it initially feels a bit more difficult to use the same volume in strength or endurance exercise as you trained with before the break (Knuiman et al., 2015).

Muscle Atrophy in Trained Lifters

Though a question remains, when do muscles of trained lifters start to atrophy? According to a review by Fisher et al., 2013:

“Trained persons performing regular resistance training are encouraged to allow adequate rest between training sessions without fear of atrophy. Brief (~3 weeks) absences from training appear not to cause significant atrophy and potentially promote greater hypertrophy upon return to training”

I looked through the studies they cite and it’s true that beginners could take 3 week breaks from training without losing mass. A different study that looks at trained powerlifters with ~8+ years of experience, found that their type II muscle fibers became ~6% smaller after a two week gym break. Though, their body weight didn’t change (Hortobágyi et al., 1993). I think it’s fair to say the “atrophy” was due to glycogen loss, as we discussed previously. A study from 2017 finds that trained men retain strength and muscle mass during a 2 week period of detraining (Hwang et al., 2017). Hence, it seems like trained lifters can take a 2-3 week break from the gym without losing gains.

I should mention that there is individual genetic/epigenetic variation to muscle hypertrophy and atrophy (Fisher et al., 2013), so it’s hard to give any absolute cut-off point. We don’t know for sure when individuals start to lose muscle mass. We have a better idea of when groups of people start to lose mass, on average. Even so, it does seem like complete bed rest (or limb immobilization) accelerates muscle loss compared to a gym break where you move around and do everyday activities (Hortobágyi et al., 2000; Dirks et al., 2016; Rudrappa et al., 2016; Cholewa et al., 2017).

Changes in LBM and muscle CSA after one week of bed rest (Dirks et al., 2016)

This indicates that a break from the gym shouldn’t include a break from movement and activity in general. It’s possible that a break leads to quicker atrophy if you’re highly sedentary. Maybe partaking in light activity maintains gains for longer? We will look at this in the next main section.

Why do I look smaller after 1 week of detraining?

You may be worried that you will lose muscle if you don't workout for a week. But let me reassure you on that:

Any size loss is most likely because your muscle glycogen and water stores become smaller (Costill et al., 1985; LaForgia et al., 1999; Mujika and Padilla, 2000; Mujika and Padilla, 2001; Nielsen et al., 2010). The good news is that glycogen levels and water stores will quickly refill once you start training again (Ribero et al., 2014). Glycogen loading increases muscle CSA (size) and lower body limb circumference (Nygren et al., 2001).

 

When do you lose endurance capacity?

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There are many ways to figure out our endurance endurance capacity and endurance performance. One of the most standard measurements is VO2max, but there are other ways as well, like heart rate variability, or time to exhaustion (how long you can run, cycle, etc. before you have to stop) . Though VO2max doesn't necessarily tell us the whole story of endurance capacity:

"Aerobic endurance is independent from VO2max , since two individuals with the same VO2max are not necessarily able to sustain the same fraction of VO2max for a given effort duration" (Bosquet and Mujika, 2012)

VO2max seems to decrease quickly when taking a break (Mujika and Padilla, 2000a; Christensen, 2011; Bosquet and Mujika, 2012). In beginners, VO2max could be reversed after 4 weeks, while highly trained athletes might lose anywhere from 6-20% in this time (Mujika and Padilla, 2000a). Time to exhaustion might be reduced from ~7% to 25% within 2 to 4 weeks (Mujika and Padilla, 2001). If we're talking more broadly, endurance performance goes down by about 4 to 25% after 3-4 weeks in trained athletes (Bosquet and Mujika, 2012). It seems like it would be best to avoid breaks that are longer than 2-3 weeks, when it comes to cardio.

How long-term detraining affects cardio, by Mujika and Padilla, 2000a.

 

Maintaining muscle mass, strength, and endurance during a longer break

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When we detrain for long periods of time we tend to lose the muscle mass we’ve gained in training (Bickel et al., 2011). However, several studies find that we can retain some of the strength we’ve gained for months (Houston et al., 1983) and years (Smith et al., 2003; Ogasawara et al., 2013a) after we’ve stopped training. Though 6 weeks could be enough to lose significant amounts of recently gained strength in trained young men (Coratella and Schena, 2016) and old men (Kalapotharakos et al., 2007). Though some studies find that people can maintain for longer (Mujika and Padilla, 2000a; McMaster et al., 2014).

However, it is clear that we don’t have to train continuously with the same intensity, volume, and frequency to maintain strength and muscle mass (Mujika and Padilla, 2000a; Ogasawara et al., 2013). Many lifters use tapering (aka deloading) as a method to prepare for meets (Mujika et al., 2004; Bogdanis, 2012; Murach and Bagley, 2015; Pritchard et al., 2015; Roberts, 2016). Here, the taper actually functions as a way to increase performance rather than decrease it (Pritchard et al., 2015; Murach and Bagley, 2015). We shouldn’t assume that a gym break or deload automatically leads to strength/muscle loss.

Though things change if you’re either injured, sick, or perhaps you’re very busy for a couple of months so you just don’t have the time to hit the gym 3-5 times a week. In that case, there are good news; you can maintain gains and strength with a much lower overall volume, and frequency.

Strength maintenance

In beginners, strength can be maintained (and even increased!) with volumes from 1/3rd all the way down to 1/9th of previous training volumes (Bickel et al., 2011). Beginners can even take multiple breaks (3 weeks) from training and still increase their strength gains at an impressive rate (Ogasawara et al., 2013). It seems like training once a week is enough to maintain gains over a period of 8-12 weeks (Rønnestad et al., 2011; Tavares et al., 2017), and perhaps even longer .

Trained lifters might want to include eccentric training into their programs before and during a period of lowered training volumes/frequencies. Eccentric movements might help retain strength for longer (Mujika and Padilla, 2000a; Coratella and Schena, 2016). If you are injured in one limb, you might want to take advantage of the cross-training effect. For example, the body increases neural adaptations (strength) in both arms even if you only train one side (Mujika and Padilla, 2000a). This might be important if you need to keep your arm/leg in a caste for a month or so. Though it’s probably not a good idea to train only one side of the body for long periods of time, due to long-term muscle mass and strength imbalances.

Muscle mass maintenance

In beginners, muscle mass can be maintained with volumes all the way down to 1/9th of previous training volumes (Bickel et al., 2011). Though, it’s generally better for gains to use at least 1/3rd of previous training volumes:

“a once-per-week exercise dose was generally sufficient to maintain positive neuromuscular adaptations” (Bickel et al., 2011)

Figures by Bickel et al., 2011

As we discussed previously, it’s also possible for beginners to take multiple breaks (3 weeks) from training and still increase their CSA gains at an impressive rate (Ogasawara et al., 2013). One study suggests beginners can maintain muscle gains for 8 weeks, only training once per week (Tavares et al., 2017)

It looks like beginners have less to lose and more to gain, no matter what they do. Sadly, I don’t have much data on trained lifters and long-term hypertrophy maintenance. Even so here’s one quote (it refers to cardio but I think the core message applies to hypertrophy as well):

“it would seem worthwhile for the injured or less active athlete to perform either a reduced training programme or an alternative form of training (i.e. to cross-train), in an attempt to avoid or reduce detraining.” (Mujika and Padilla, 2000a)

Similarly to strength, eccentric training could help prevent muscle mass loss:

Eccentric training (ECC) increases and maintains chest circumference after 6 weeks in trained lifters (3 years experience). TRAD = Traditional training. CONC = Concentring-only lifting (no eccentric portion). CON = Control group. Figure by Coratella and Schena, 2016.

Maintaining endurance

Once we start taking longer breaks from endurance training, i.e. 5 weeks, our cardio "gains" quickly diminish (Maldonado-Martin, 2016). Though, there are ways to prevent this. Several research teams now advise athletes to keep training during the off-season, or if they are injured (Joo, 2016; Maldonado-Martin, 2016). Here are some ways to maintain endurance capacity during breaks from regular training:

• If injured, such as Achilles tendinosis or ankle sprain, use alternative training methods such as underwater running, cycling, or perhaps rowing (Bosquet and Mujika, 2012)
• Reduced training programs (see quote below) (Rietjens et al., 2001; García-Pallarés et al., 2009; Joo, 2016)
• Use completely different training methods. For example, several studies suggest that strength training can improve endurance and VO2max (Aagaard and Andersen, 2010; Sunde et al., 2010; Louis et al., 2011; Ozaki et al., 2013; Rønnestad and Mujika, 2014; Vikmoen, et al., 2016a)

“Several studies have indicated that the maintenance of training intensity during periods of reduced training and taper (...) is of paramount importance in order to keep training-induced physiological and performance adaptations. [59,64,68-74] On the other hand, training volume can be reduced to a great extent without falling into detraining. This reduction can reach 60 to 90% of previous weekly volume, depending on the duration of the reduced training period, both in highly trained athletes and recently trained individuals. [28,29,57-60,63,69-8]”

“Finally, reports from the literature indicate that training-induced adaptations are readily maintained for several weeks during periods of reduced training frequencies, but the reductions should be more moderate in athletes (no more than 20 to 30%) than in recently and moderately trained individuals (up to 50 to 70%)." (Mujika and Padilla, 2000a)

Muscle memory
Regaining lost muscle and strength

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Whenever we do strength training, our muscles add nifty little things called myonuclei (Kadi and Thornell, 2000; Petrella et al., 2008; Verdijk et al., 2009; Bellamy et al., 2014; Roberts et al., 2015; Gundersen, 2016). These myonuclei are important when it comes to hypertrophy. Some argue the nuclei are added before hypertrophy (Gundersen, 2016) while others suggest nuclei only seem to be added once a hypertrophy threshold is reached. They argue the threshold is 26% muscle fiber growth (Kadi et al., 2004):

“(...) significant increases in myonuclear number have been reported in studies where muscle fibres had hypertrophied by more than 26% (Cabric & James, 1983; Allen et al. 1995; Hikida et al. 1998; Roy et al. 1999; Kadi & Thornell, 2000) but not by 6.8–15.5% (Giddings & Gonyea, 1992).”
(Kadi et al., 2004)

Before and after 10 weeks of strength training in women (Kadi and Thornell, 2000)

How are myonuclei relevant to detraining?

Once you become trained and have gathered extra myonuclei, you’d want to keep them throughout detraining. The good news is that myonuclei seem to stay in muscles, even when detrained for long periods of time (Gundersen, 2016). Myonuclei might remain for 15 years or more in human muscles (Gundersen, 2016). This phenomenon has been called “muscle memory”, because the muscles seem to remember their former glory (Gundersen, 2016). The idea is that you can quickly return to previous training levels and regain muscle size if you’ve been highly trained before. Though, most studies on muscle memory and performance are done on animals (Bruusgaard and Gundersen, 2008; Bruusgaard et al., 2010; Egner et al., 2013). There are some studies that look at muscle memory during detraining and retraining in humans, but they are low quality (Staron et al., 1991).

Muscles quickly returning to previous size levels after a detraining-retraining routine (Gundersen, 2016) (figure adapted from Bruusgaard et al., 2010)

Steroid users seem to have more myonuclei (Kadi et al., 2000; Yu et al., 2014), and the myonuclei could remain in their muscles for a long time. This has implications for banning steroid users from sports; maybe bans should be longer due to the long-term advantage the extra myonuclei give users (Gundersen, 2016).

Other “comeback” mechanisms

Several studies show that the body can maintain muscle size and strength over periods of detraining. This could lead to quick gains after detraining, similarly to when you started training for the very first time (Bruusgaard et al., 2010; Fisher et al., 2013).

Researchers speculate that periods of detraining makes the muscle more sensitive to anabolic signalling. Hence, detraining or deloading might actually be beneficial to gains in the long-term (Ogasawara et al., 2012; Fisher et al., 2013; Schoenfeld et al., 2014). As Schoenfeld et al. (2014) have described it:

“As an individual gains lifting experience, a "ceiling effect " makes it progressively more difficult to increase muscle mass, perhaps mediated by an altered anabolic intracellular signalling cascade (Coffey, Zhong, et al., 2006; Ogasawara, Kobayashi, et al., 2013). ”

If we want to use speculative data, we could look at anabolic signalling mechanisms like mTOR:

“with chronic resistance training, anabolic signaling becomes less sensitive to resistance exercise stimuli, but is restored after a short detraining period.” (Ogasawara et al., 2012)

Indeed, two studies by Ogasawara et al. suggest that strength and hypertrophy quickly rebound in beginners who take three week training breaks from lifting (see “when do you lose…” muscle mass and strength sections above for images) (Ogasawara et al., 2011; Ogasawara et al., 2013):

“Our results are in agreement with those of the previous cellular and molecular studies. Chronic muscle contraction induces a variety of metabolic and morphological adaptations in contracted skeletal muscles for maintaining homeostasis and minimizing cellular disturbances during subsequent training sessions (Gordon et al. 2012 ; Hubal et al. 2008 ). In the muscle, anabolic mammalian target of rapamycin (mTOR) signaling and protein synthesis responses to resistance exercise are attenuated by chronic resistance training (Coffey et al. 2006 ; Phillips et al. 1999 , 2002 ; Tang et al. 2008 ). These results may explain the attenuated muscle hypertrophy response observed during the late phase compared to the early phase of resistance training.“ (Ogasawara et al., 2013)

This isn’t necessarily because of anabolic resistance or myonuclei, because the study participants were beginners. But, the studies do suggest that there are mechanisms that make it easier to “come back” after 3 weeks detraining in beginners. Maybe the same happens in trained lifters?

 

Other effects of detraining

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I added this section for those that are interested in the various technical aspects of detraining.

Flexibility

“It has been shown that 4 weeks of training cessation significantly lowered the flexibility of hip, trunk, shoulder and spine by 7.4 to 30.1% in male and female physical education students” (Mujika and Padilla, 2000)

Muscle characteristics

Table by Mujika and Padilla, 2000

Cardiovascular characteristics

Table by Mujika and Padilla, 2000

Metabolic characteristics

Table by Mujika and Padilla, 2000

Table by Mujika and Padilla, 2000a

Conclusion

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The evidence suggests that  both trained athletes and beginners can maintain their strength, muscle, and endurance gains for at the very least 2-4 weeks without much training. During detraining, muscles carry less glycogen and water so they seem smaller. The good news is that it's relatively easy to maintain gains in short periods of time. Training volume and frequency can be reduced, but intensity should remain the same. The body also has various mechanisms it can use to "come back" from detraining quickly.

Limitations

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• Glycogen confounds CSA gains (https://www.ncbi.nlm.nih.gov/pubmed/11903130)
• Most studies are on 20-something university student males, though there are some studies on elite athletes and older people as well. Women are generally not represented in these studies.
• It’s possible some participants kept training during detraining periods. We can’t know for sure without monitoring them and their gym access.
• Ecological validity: most studies only use 1-3 exercises for one body part. It’s possible things would change with whole-body programs