It happens to all of us at some point. We suffer an injury, take a long trip or vacation, or even experience true overtraining (1–3), leaving essentially no choice but to take a break from training. The cards are dealt and you’re handed the most dreaded of fates—the “D word” (detraining).

When it’s time to get back in the saddle, most iron addicts are itching to go full bore, “gung ho from the get go” to get back to previous strength, size, performance, and appearance. Long standing forms of linear periodization (e.g., Matveyev’s classic model [4, 5]) along with common sense suggest easing back with lighter loads (perhaps with higher training volume) to reverse off-season deconditioning. The coaches reading this have probably witnessed detraining in athletes after a long (sometimes lazy) off-season. Many of you may also be personal trainers who have “seasonal” clients or those who “fall off the wagon” due to work, finances, or even snow birding. Trainees return to you in a state of training far different than the last time you worked with them.

Naturally, the principle of reversibility applies here: Your gains will be reversed when the stimulus of adaptation is lost (6, 7). But really, aside from a bruise to the ego, how much does one lose in only a few weeks or months after training for years? Are losses greater or more rapid in the highly trained or more so in relative newbies to the iron game?  How fast do gains come when starting back in the gym? Is it necessary to blast full bore into one’s previous training schedule and simply suffer with extreme soreness and (potentially dangerous [8]) muscle damage? I think that we’ve all heard and/or seen the horror stories—personal trainers pushing clients far beyond what’s necessary for a first training session followed by a predictable no-show for the next appointment. (This obviously isn't necessary or good for business.)

In the beginning

It’s commonly understood (and supported with research) that the initial, relatively rapid gains in strength with a novel weight training regime are primarily neurological in nature (9, 10). Maximal muscle electrical activity (indicative of neural activation) increases rapidly, substantially, and in parallel with strength gains (11, 12) and to a greater extent than muscle cross-sectional area (13).

scott stevenson training muscle memory 052014

On the other hand, muscle remodeling does indeed begin from the first workout. (Ever been surprised how sore you were from something really “easy” after a layoff?) It just takes one bout to stimulate contractile protein and collagen synthesis (14). In fact, type II muscle fiber type interconversions and strength gains are quantifiable within two weeks of training onset (15, 16). One study has even found significant increases in muscle thickness after only two training sessions (17). Heck, only twenty-four (twice daily for six days/week) blood flow restriction training sessions spread out over two weeks produced increases in muscle volume of 8–10 percent (18). (These kinds of gains, even when spread out over two months, are substantial and visibly noticeable (19, 20).)

Something else pretty cool happens when muscle grows from repeatedly banging away in the gym. Because skeletal muscle fibers are relatively large, they must be populated by many nuclei, hypothetically such that each nucleus governs a relatively consistent volume of the cell, otherwise known as its “myonuclear domain" (21, 22). Thus, as muscle fibers enlarge, nuclei are typically added as satellite cells (23) sandwiched between regular muscle fibers (24) and undergo division and donate nuclear (genetic) material. This maintains myonuclear domain size and keeps order in the growing fibers (25, 26). In fact, myonuclei may be added even before the muscle cell begins to get bigger (27), underscoring the importance of even distribution of these localized “genetic outposts” during the hypertrophic remodeling process (28). This is a major restructuring of the muscle cell of course. While a short period of training (one to three months) may cause muscle satellite cells to proliferate (increase in number), if training stops, this extra nuclear material never makes it into the fibers themselves as actual myonuclei (29). (Make note of this, as these satellite cells seem to be intimately involved in the phenomenon of “muscle memory,” discussed in Part II of this article series.)

The deload—no big worries

In my experience coaching and training clients, when the structure of a deloading period (several days up to a couple weeks) is left to the individual, loss of strength is highly variable. Some clients come back refreshed and stronger whereas others have taken a step back, which is quickly regained.

This variability is likely dependent upon the frequency (30) and intensity (31–33) of whatever training takes place during the deload. The overreaching status of the trainee before the layoff probably plays a part as well (1, 2) not to mention diet and other lifestyle factors. An athlete who spends his deload week hitting the craps tables in Vegas might come back less refreshed (and weaker) than one who enjoys a mini-vacation barbequing and lounging by the pool.

female study jennifer petrosino squat scott stevenson 052014

It seems plausible that just as the adaptation to training is variable but somewhat genetically determined (34), the results of detraining may vary similarly but also be predictable based on the initial state of training. Let’s take a closer look.

Strength detraining and jogging your muscle memory

Here you are after many weeks or months of real detraining. You’ve done nothing in the gym for a long while. Obviously, the mirror gives some indication of your relatively slovenly status, but the mind can play tricks as well. What does exercise science tell us to expect on the fateful first day back?

Some early research (in the 80s and 90s) indicated that the time course of strength and muscle size loss follows a somewhat similar (reversed) pattern during detraining (13, 35). For instance, a well respected group of Finnish researchers found that 50 percent of strength gained over sixteen weeks of training was lost in eight weeks of detraining (11).

A longer study of (quite brutal) training and detraining paints a more optimistic picture. Ohio University researchers set out to examine the concept of “muscle memory” in two dozen women who trained the lower body for twenty weeks (twice weekly performing 3 X 6–8 reps to failure of squats, leg presses, knee extensions, and hamstring curls). They roughly doubled strength and increased the size of their type II muscle fibers by about 50 percent (36). (By the way, skin folds dropped substantially and their thigh and gluteal circumferences were unchanged. I would be willing to bet that there were some pretty impressive transformations among these subjects.) Six of the women came back after seven to eight months of detraining to find that they’d only lost about 50 percent of their gains in strength, but size was preserved in the type I and IIA muscle fibers. (Only the type IIB fibers, which were likely not used regularly during many daily activities (37), atrophied significantly (38).) When these hardy half-dozen retrained, they rapidly recovered their gains in strength and fiber size in only six weeks.

A more recent study also found that strength gains after only nine weeks of training were preserved after about seven months of detraining in both the young and old (39). Other research has shown remarkable preservation of strength (but less so for power) in recreationally trained men who discontinued their usual routines for six weeks (40). Also, recently acquired eccentric strength may be better preserved than concentric strength (41), perhaps because the ability to disinhibit force production (force production is inhibited neurologically during eccentric actions [42]) is better retained (43, 44) during detraining.

Keep some of it

So it seems that the “use it or lose it” adage is not entirely true when it comes to muscle strength and size. In Part II of this article, we’ll take a closer look at “muscle memory” and how it is that years in the weight room can pay long-term dividends even after taking a prolonged break from heavy lifting.


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