(Originally published by me at )

Yesterday I did many sets of few reps of empty bar snatches. After that, some drop snatches and presses. I got tired, my breathing was labored but I was happy: I’ve been ill during the past four months and it felt good to move. I barely managed to maintain a low volume and intensity in strength training for two months, insisted on a little treadmill walking to avoid insanity for another month and then nothing. I was basically slithering around the house under heavy medication, mildly stoned and weak. My strength and my conditioning decreased dramatically.

What happened to my bone metabolism? The quality and functioning of my skeletal muscles? My inflammatory indicators? My body composition (lean and fat mass)? They were all negatively affected. This is what we call “detraining”.

If one is an athlete, after a period of detraining there is usually a period of retraining. “Retraining” is the set of adaptive responses to resuming training after a period of training cessation. The more experienced the athlete, the faster the retraining period up to performance levels before detraining.

There is not a lot of research about detraining and retraining. A Pubmed search with the title search term “detraining” resulted in 390 items (all time). The same search with the term “retraining” resulted in 915 items (all time). Most “retraining” titled articles are not related to sports.

My goals with this article are:

  1. To assess the state of the art on the present scientific knowledge about training and retraining;
  2. Whenever possible, to point out what health care professionals, coaches, and athletes might expect in detraining and retraining.

It might not be much but there’s a reason for this choice: detraining and retraining are both scary. Detraining is often a process that follows injury or illness, both negative experiences with frequently unknown consequences over an athlete’s performance. Retraining is something athletes usually engage in eagerly and with great expectation. Also, with great anxiety.

A little bit of knowledge can go a long way in managing this kind of stress.

What is Detraining

Screenshot 2019-10-14 10.33.01

Detraining is not just to “stop training for a while”. Detraining is the set of physiological responses to the cessation of training. It frequently results in loss of performance. The exception is when detraining happens after a period of overtraining and burnout and performance gains are observed in the absence of retraining.

Detraining can be a serious process. It can be even more serious for high performance and elite athletes, even at a young age and for short periods. Sung et al (2017) demonstrated that a two-month detraining period resulted in adverse effects on early atherogenic dyslipidemia development, progressing insulin resistance, low-grade inflammation, and visceral adiposity in young elite taekwondo athletes.

Another study on elite male soccer players examined their bone metabolism (Koundourakis et al 2018). A six-week supervised detraining was sufficient to cause suppression of bone-formation rate and a parallel induction of bone resorption.

Several studies suggest oxidative capacity decrease after detraining (Liao et al 2016). The decrease in energy metabolism enzymes and ATP production led to the hypothesis of decreased mitochondrial content in the muscle fiber (Chi et al 1983, Staron et al 1981, Wibom et al 1992).

mitochondria training retraining

Kirshner’s interpretation of Wibom et al (1992) 

The claimed mitochondrial content effect was never measured and one case study about a detrained powerlifter suggested exactly the opposite (Staron et al 1981): the authors’ hypothesis was that the mitochondrial content of the detrained fiber remains constant (for a strength-trained muscle), but as the volume of the fiber decreases, the mitochondrial volume percent increases.

The cause, type of sport, age and period of detraining are important factors concerning observed physiological results. More than one study shows that a four-week detraining period may have negligible effect on performance (McMahon et al 2019, Kraemer et al 2002). All other things being equal, there is a dose-response to time in strength loss (Bosquet et al 2013). This hypothesis was also confirmed by Vassilis and collaborators (2019) with young soccer players submitted to a four-week period of detraining, with no measurable effect on isokinetic strength on their lower limbs.

What is Retraining

Screenshot 2019-10-14 10.38.16

Trained individuals, limbs and even muscles respond better and faster than “naïve” ones (previously untrained). This had been observed by athletes and coaches since time immemorial. A few decades ago, it was termed “muscle memory”. Experimental results from animal models show an increased response from pre-trained versus naïve individuals even for short training periods and long detraining ones (Lee et al 2016).

Between 2010-13, the scientific community embraced the cellular explanation for the “muscle memory” phenomenon (Gundersen 2016):

muscle memory

The mystery seemed to have been solved but we probably celebrated too early. Evidence suggests that the elevated myonuclear density acquired during training is lost during detraining (Dungan et al 2019).

Psilander and collaborators (2019), studying humans, observed a 20% strength increase in the trained group versus a 5% increase in the untrained group in the first training period, comparable to the muscle thickness (proxy to hypertrophy) response, although after the detraining and retraining, no differences in myonuclei density were observed.

We still agree that “muscle memory” exists but it doesn’t seem to be mediated by myonuclei density as previously thought (Murach et al 2019). New studies on epigenetic phenomena associated with skeletal muscle hypertrophy/atrophy are promising and offer plausible alternative models (Seaborne et al 2018).

muscle memory epigenetics
Screenshot 2019-10-14 10.45.29

Disease, Injury, and Planned Detraining

As is probably clear by now, the reason why detraining happened in any specific case is an important factor in how serious the health consequences acquired during detraining are and how retraining takes place. The main reasons for training cessation among athletes are injury and illness (Timpka 2014). There are two measures that matter in sports injury and illness epidemiology: incidence and burden, expressed as the number of lost days, hours or competitions.

Disease, Injury, and Their Burden

Screenshot 2019-10-14 10.47.40

Bahr and collaborators (2018) have argued that we must shift our focus from injury and illness incidence to burden because both individually and institutionally, that is what matters. If a low burden injury has a high incidence, it affects the athlete, the team and the sponsors much less than high burden injuries with a lower incidence, but enough to damage the patient’s athletic life, the team prospects, and the sponsors’ investments.

The picture below illustrates this point: while lower leg contusion has a high incidence on football, it has a low burden. ACL tears, on the other hand, have a high burden.

lost days - burden

From Bahr et al (2018)

Different sports have different incidence and burden rates for injury and disease. It is important to observe that incidence and burden are very different for each type of injury. Acute injuries can have a lower incidence and higher burden or vice-versa.

why we should focus 3

From Bahr et al (2018)

Burden and incidence can be different for the training period and competition. Most coaches and athletes are painfully aware of the reality shown in the picture below: while injury incidence is lower in the final phase, when it happens, it tends to be worse and cause a higher number of lost days, and, frequently, lost competitions.

why we should focus 2

The number of lost days (and detraining) among elite athletes can represent a good part of the competitive year. A study conducted in Ireland showed that the average athlete suffered the effects of sports injury for 52 days in a year. More time was lost through overuse injuries than acute injuries. The injury rate per 10,000 hours of participation was lowest in noncontact and explosive sports and highest in contact sports. However, when expressed in terms of days lost per 1000 hours of participation, endurance sports had the lowest burden of time loss and explosive sports the highest (Watson 1993). In terms of the amount of time lost due to injury, elite gymnasts spent 20.2% of the year’s training time at less than full capacity, compared with 13.9% for the nonelite gymnasts. (Kolt et al 1995). In a study with collegiate female athletes, during the 12 recorded months, lost-time injuries occurred in 31.4% of the athletes (Walbright 2017). Among Brazilian Jiu-Jitsu athletes, players missed an average of 35.9 ± 60.1 days of practice due to BJJ-related injury in 12 months (Usuki et al 2017).

time lost by sport Ireland

From Watson 1993.

time lost 12 Ireland

From Watson 1993.

Planned Detraining

Planned detraining may not be detraining proper or it may be a training strategy when competing physiological adaptations are involved. This is known as “concurrent training and retraining” and is mostly applied to track and field and team sports (Sousa et al 2019).

Screenshot 2019-10-14 10.57.10

The exact mechanisms involved are unknown but the strategy has been used intuitively and successfully by powerlifters since there is any record of programming. Recent studies simply confirm that a period of training cessation of a little less than a week is, on average, optimal (Pritchard et al 2017, Pritchard et al 2016).

Much research is needed to start to understand the nature of the beneficial short-term training cessation. A few interesting molecular studies have been conducted and we might have a better understanding of the involved phenomena in a couple of years (Ogasawara et al 2013).


Screenshot 2019-10-14 10.59.32


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