Strength training: the true cost of a break

Reversibility of strength

When it comes to strength losses as a result of detraining, the research is even sparser, especially when it comes to athletes in regular training, which means looking at data from the general population. One 2019 study looked at the effects of 12 weeks of resistance training in middle-aged adults, and how much of the strength gains were lost after 12 weeks of detraining⁽²⁾. It found that detraining losses in absolute strength and local muscular endurance were around 15%. Another study looked at older adults who resistance trained for 12 weeks (using either high or low-intensity training) then detrained for 24 weeks⁽³⁾. It found that the gains in muscle volume were completely reversed after 24 weeks; however, some of the gains in functionality were retained, especially in those who had undertaken the high-intensity protocol.

Another study in the form of a systematic review (a study that pools the data from a number of previous studies) looked at the development, retention and decay rates of strength and power measures in elite rugby union, rugby league and American football players⁽⁴⁾. It found was that after a 7 to 8-week period of detraining, the recorded strength and power losses averaged between 14-15%. Interestingly, the strength losses here occurred twice as fast as those of the middle-aged adults in the study above.

Strength loss after short breaks

While the above findings clearly demonstrate the principle of reversibility when it comes to fitness and strength, they may have limited relevance to most athletes most of the time. That’s because when a forced break from training occurs – for example due to injury, illness, a holiday etc – the period away from training is rarely more than one to four weeks. However, most studies on strength loss as a result of training reversibility involve much longer periods of inactivity (handy for researchers as they can more easily observe large measurable effects!). In addition, there’s little attention been paid to what really matters to athletes: ‘How quickly can I get back to my previous fitness level once I resume training, and are there any longer-term consequences of my training break?’

There is some encouraging evidence on this topic for athletes who need to take a relatively short break (less than four weeks), because research suggests that muscle strength and size are generally well maintained after these time periods^(5,6). However, when the break from training exceeds four weeks, losses in muscle strength and particularly muscle size seem to be inevitable (as would be expected)⁽⁷⁾.

The good news for regular strength trainers though is that when an extended break from strength training occurs and strength/muscle size is lost, fitness can be regained faster once strength training is resumed compared to those who are not in regular strength training^(8-10). This accelerated regaining of strength is most likely due to a ‘muscle memory’ effect, whereby the genes involved in training adaptation are able to switch back on more rapidly compared to switching on for the first time⁽¹¹⁾.

Questions

Here’s a question: if taking a short break from training results in minimal strength losses and if resuming training again after a longer break results in much more rapid regaining of strength compared to the initial training required to produce that strength, does it really matter if athletes who need strength take infrequent or even frequent breaks? This is difficult to answer because firstly, most of the research on this topic has been gleaned not from athletes in high-level training, but from studies on older or previously untrained adults. The answer will also depend on the duration of any break and how many breaks there are in a given period. That’s because even if strength losses are minimal over a break, by definition, you are not training, which means you cannot be gaining strength, in turning meaning your progress over a season may be reduced.

There is some evidence that a short, one-off break may not result in any performance loss at all. In a 2011 study, researchers compared 15 weeks of continuous strength training with six weeks on, a 3-week break, followed by another six weeks on⁽¹²⁾. At the end of the 15 weeks, they found no differences whatsoever between the two groups in muscle cross-sectional area and one repetition maximum (1-RM) adaptations. The same group of (Japanese) research also found no differences in muscle cross-sectional area, 1-RM, and maximum voluntary isometric contraction between a 24-week period of unbroken training and 6 weeks on, 3 weeks off, 6 weeks on, 3 weeks off, 6 weeks on schedule (ie 24 weeks with two x breaks of 3 weeks)⁽¹³⁾. Another study compared upper and lower body adaptations in muscle strength and size between a group performing continuous strength training for ten weeks and a group performing two 5-week strength training periods separated by a 2-week detraining period⁽¹⁴⁾. After the intervention, they found no significant differences between the groups for any measures of muscle strength or size.

Resuming training after longer breaks

The evidence suggests that when there are short interruptions (under four weeks) to strength training, there may be very little or no negative consequences. This is most likely due the muscles being able to make a deep recovery during the break, and the fact that muscle memory very quickly abolishes any decrements produced by that break. But what about taking a long break then resuming training after that long break? To get some answers, we can turn to brand new research by a team of Finnish scientists. Published in the Scandinavian Journal of Medicine and Science in Sports, this study compared the effects of a 20-week strength program containing a 10-week break in the middle (ie 10 weeks on, 10 weeks off, 10 weeks on) with a 20-week period of continuous unbroken strength training⁽¹⁵⁾.

What they did

Fifty-five eligible healthy (but not experienced in resistance training) males and females participated in the study. To qualify, participants had to be aged 18–40 years, not be engaged in resistance or endurance training, have a body mass index (BMI) within the range 18.5–30 kg/m², and not be using any anti-inflammatory drugs (NSAIDs). The participants were then randomly assigned to the continuous 20-week long resistance training group or the interrupted training group (10 weeks on, 10 weeks off, 10 weeks on) with the same total training time but with a 10-week break in the middle. To avoid any unwanted bias due to sex or body composition, male and female participants were also divided into matched pairs using a combined score for BMI and age.

In the interrupted training group where participants took a 10-week break after the first 10-week training period, the instruction was to resume their normal, habitual lifestyle but to avoid any form of resistance or endurance-type training or any other unaccustomed exercise for that 10-week period. To ensure this was the case, physical activity and other lifestyle changes during the detraining period were assessed with a survey, and the participants were also contacted via email in the middle of the detraining period to ensure that they did not participate in any form of resistance training.

The training

In terms of the actual training undertaken, two whole-body sessions were performed a week, with at least 48 hours between the sessions. The training protocol was based on proven published research for promoting gains in both muscle size and strength (eg the use of moderate-to-high loads, 2-3 sets per exercise, and combining different exercises for the measured muscle groups). The exercises were as follows and conducted in the following order:

·        Leg press (4 × sets of 8–10 reps)

·        Leg extension (4 × 8–10 reps)

·        Smith machine bench press (3 × 8–10 reps)

·        Barbell biceps curl (4 × 8–10 reps)

·        Chest supported seated row (4 × 8–10 reps).

All sets in each exercise were performed consecutively before moving on to the next exercise. Participants were instructed to conduct the concentric (lifting) phase of the exercises as fast as possible (ie with maximal effort) and the eccentric (lowering) phase under muscular control and to last approximately two seconds. All the exercises were done with 2-minute rest periods between each set. The participants started the training with loads corresponding to 70% 1-RM in leg press, Smith machine bench press, and chest-supported seated row exercises, and 50% 1-RM in biceps curl and knee extension exercises. They were instructed to perform 8–10 reps in each set with approximately 1–2 repetitions in reserve, except in the final set of each exercise in the second training session of every week, when the last set was performed until failure.

What they measured

Immediately prior to commencing the intervention, and then every five weeks until the end of the intervention, testing was carried out to monitor the progress of participants in both groups. These were:

·        Muscle strength testing - Dynamic muscle strength from the lower and upper body was assessed by leg press and barbell biceps curl one repetition maximum tests (1RM), respectively.

·        Muscle size measurement - Vastus lateralis (of the quadriceps) and biceps brachii (of the upper arm) were assessed using ultrasound to determine cross sectional area (in cm²).

·        Jump height – this was assessed using a countermovement jump test.

At the end of the training period, the results from both groups were collated and compared.

What they found

As expected, in the interrupted training group, the 10-week break resulted in performance declines. In particular, the 1-RM for both the leg press and biceps curl declined significantly, as did the scores in the countermovement jump height test. Also, the cross sectional area (ie muscle size) of the vastus lateralis and the biceps brachii declined. However, at the end of the total training period, both groups very significantly increased their 1-RM for the leg press and the biceps curl compared to the start. The same was true for muscle cross-sectional area and the countermovement jump height.

Remarkably and importantly however, there was no difference in the gains achieved by both groups over the course of the whole intervention – ie the group that took a 10-week break performed just as well after their second 10-week training block as the group that trained uninterrupted for 20 weeks (see figure 1). This was because during the first five weeks of retraining in the interrupted group, increases in 1-RM scores and muscle size were much greater than in weeks 10-15 of the continuous training group. These rapid gains upon resuming training (most likely due to the muscle memory effect) basically allowed the interrupted trainees to ‘catch up’ with the continuous trainees, an effect that continued to a lesser extent during weeks 15-20!

Figure 2: Changes in 1-RM and muscle size over time

Red plots = continuous training; blue plots = interrupted training. A and B = 1-RM scores for leg press and biceps curl. C and D = muscle cross-sectional area for vastus lateralis and biceps brachii. Note that the 10-week decline in the interrupted group was only partial, and that upon training resumption, the gains were very rapid, allowing the participants to catch up with their continually trained colleagues. 

Implications for athletes

In their summary, the authors recommended that ‘trainees should not be too concerned about occasional short-term training breaks in their daily lives when it comes to lifelong strength training’. In other words, when you take a longer-term view over many months or years, even a 10-week break is not going to set you back to any significant degree once you resume training. That’s great news because it means that if you are unlucky to suffer a longer term injury or find yourself in circumstances where it’s difficult to strength train (eg an extended trip abroad), you really don’t need to worry too much about losing out in the longer term. These findings also support the notion of taking an annual break for a couple of months – for example over Christmas and New Year, in order to allow for deep rest and recovery.

A couple of caveats are worth mentioning however. Firstly, the subjects in this study, while reasonably fit and healthy, were not athletes undergoing high level training. While the same physiological principles apply, athletes who have achieved or are maintaining a peak of strength may find it harder to regain that peak as easily as those who are less highly trained. Therefore, they may prefer to take shorter breaks and not to pick up an injury requiring an extended break.

It’s also worth remembering that this study compared 20 weeks of training with and without a 10-week break. What it did NOT do was compared 20 weeks of training with a 10-week break to 30 weeks of uninterrupted training, which is what many athletes would hope for during a training program! It’s likely that the performance gains after 30 weeks of uninterrupted training would be greater than a 30-week period where only 20 weeks involved training and a 10-week break was taken in the middle.

Finally, this study looked at the effects of just one break in isolation. It’s not possible to say what the effect would be if two or more breaks were taken within a limited timeframe. It could be the cumulative performance effects of time missed from training could be more negative. Overall however, athletes can still take heart; unplanned events in life happen and when they do, it’s reassuring to know that your long-term strength gains are unlikely to be compromised!

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