August 11, 2020

What determines the training frequency?

The training frequency for bodybuilders or recreational strength athletes with the aim of building muscle mass is a hotly debated topic.

A quick look online will show that expert opinions vary widely when it comes to the ideal training frequency for strength training with the goal of building muscle.

Some authorities recommend training a muscle very often, while others (especially those closer to mainstream bodybuilding) continue to suggest training each muscle only once a week. Those who follow the scientific literature quite dogmatically will point out that recent meta-analyses have reported that an ideal training frequency is two to three times a week, even though most bodybuilders continue to train their muscles once or twice a week.

The decision to train a muscle two or three times a week is a big decision that will have a big impact on how you should set up your training program. At this point in time, the available scientific literature does not have the level of precision we would need to determine an optimal training frequency based on the numbers from long-term studies.

What factors can influence training frequency?

Training frequency can be influenced by the duration of time during which the muscle protein synthesis rate is increased after a training session. In addition to this, the ability of the exerciser to recover after the first training session also plays a role. This is related to the after-effects of fatigue on the hypertrophy stimulus of the second training session.

Let's look at both factors below.

1. changes in the rate of protein synthesis

During a strength training session, the fibers of a muscle experience a mechanical load. This mechanical load is perceived by mechanoreceptors, which leads to an anabolic signal sequence. This signaling sequence triggers an increase in the rate of protein synthesis within each loaded muscle fiber. This increased internal rate of muscle protein synthesis is what causes increased protein content within the exercised muscle fibers.

After the training session, the rate of muscle protein synthesis increases over several hours, eventually reaching a maximum value and then decreasing again. We can plot these changes over time as a curve and the area under this curve is the overall effect of the training session on the size of the muscle fiber. If the rate of muscle protein synthesis is increased more or over a longer period of time, the corresponding muscle fiber will experience a greater increase in size.

Logically, it makes sense to wait until the rate of muscle protein synthesis after a training session drops back to approximately the pre-training session level before performing the next training session, as otherwise the stimulus generated by the second training session would be partially wasted. For this reason, the length of time over which the rate of muscle protein synthesis is increased after a training session is quite important.

As the figure below shows, the curve differs between trained individuals (blue) and untrained individuals (red). In untrained individuals, it takes longer for the rate of muscle protein synthesis to reach its maximum and it also takes longer for the rate of muscle protein synthesis to return to its starting point, resulting in a larger area under the curve.

In addition to this, the curves also differ depending on which proteins are measured. If we look at all proteins in a muscle fiber (continuous curves), the curve shows a different profile than if only the contractile proteins (dashed curves) are measured.

We should note that both myofibrillar and mixed muscle protein synthesis rates can be increased for the purpose of increasing muscle fiber size and for the purpose of repairing damaged muscle fibers, which occurs in the contractile and non-contractile protein areas. Therefore, an increase in the rate of (myofibrillar or mixed) protein synthesis does not automatically mean that the muscle fiber is building new proteins to increase in size - it could simply be repairing damage that has occurred.

If we look at all proteins in untrained individuals, the rate of mixed protein synthesis reaches its maximum value after 16 hours and has not dropped back to the pre-training baseline after 48 hours. If we look at the shape of the curve, it suggests that the rate of mixed protein synthesis reaches its baseline value after about 72 hours, which would imply an ideal training frequency of every three days or twice a week.

Since the curve peaks and declines more quickly in trained individuals, this data suggests that more frequent training would be ideal. However, it should be noted that this analysis is limited by the fact that all muscle fiber proteins are taken into account.

Ideally, a similar analysis would be performed looking only at the contractile proteins, but such a study has not yet been published. However, scientific research has shown that the increase in the rate of myofibrillar protein synthesis over a 48-hour period is closely related to the hypertrophy that results from a strength training program - but only when the individual is trained, but not when they are untrained.

This suggests that most of the increase in myofibrillar protein synthesis rate in trained individuals occurred within 48 hours, implying an ideal training frequency of at least every other day or three times per week.

2 Regeneration of the trainee

Immediately after a strength training session, we experience a reduced ability to release strength. There are three factors responsible for this effect:

peripheral (local) fatigue of the muscles
muscle damage
exhaustion of the central nervous system

It is important to understand that the influence of each of these three factors changes over time.

Peripheral (local) muscle exhaustion may result from reductions in the activation of individual muscle fibers (through a reduction in the sensitivity of actin-myosin myofilaments to calcium ions or a reduction in the release of calcium ions from the sarcoplasmic reticulum) or from factors that affect the individual's ability to produce force. The latter includes an impairment in the function of the actin-myosin cross-links. But however this fatigue occurs, it is only temporary.

We recover from peripheral fatigue within a few hours.

Muscle damage can include many things. These include very small amounts of damage to internal structures within the muscle fiber, such as the cytokine skeleton or contractile proteins. In fact, one of the most common signs of mild muscle damage is displacement of the Z-disks - lines that separate one sarcomere from the next. Muscle damage can also include tears to the cell membrane and more serious damage can include complete rupture of the muscle fibers themselves.

All of these types of damage are repaired by extending the structures of the existing muscle fiber. Very severe damage cannot be repaired and this leads to fiber necrosis. When this occurs, the remnants of the old muscle fiber are completely degraded by proteases and a new muscle fiber grows within the cell membrane of the old muscle fiber (1, 2).

Some types of strength training involve little or no muscle damage, while others involve a large amount of muscle damage. Muscle damage can also vary between muscle groups, muscle fiber types and individuals. Depending on the degree of muscle damage, the duration of the repair or regeneration process can take anywhere from very short to several weeks.

Central nervous system fatigue can result from either a reduction in the strength of signals sent from the brain or spine or an increase in feedback that reduces the excitability of motor neurons. Central nervous system fatigue is not the same as an unwillingness to perform the next training session, which is more closely related to the amount of muscle damage we have experienced. Rather, it represents the degree to which we can voluntarily activate the trained muscle.

Central nervous system exhaustion after strength training is less and of shorter duration than most people believe, which is probably related to some confusion about the meaning of the term. We assume that because we don't feel ready for the next training session, we must experience central nervous system fatigue, which is not necessarily the case. Incidentally, central nervous system fatigue tends to increase with increasing exercise duration rather than intensity, which makes it more pronounced after endurance training.

However, if the muscle damage is severe, such as after unaccustomed purely eccentric training or a high volume of conventional strength training (3), then this can cause prolonged periods of central nervous system fatigue that can last up to 2 or 3 days after training.

The three types of fatigue mentioned above have different effects on the impact of subsequent training sessions.

If we are still experiencing peripheral fatigue at the time of a subsequent training session (which would be very unusual as it would require a second training session within a few hours of the first) then this does not affect the hypertrophy stimulus.

The high level of peripheral fatigue leads to an increased recruitment of motor units and a reduced shortening speed of the muscle fibers, which means that our high threshold motor units are recruited earlier and we perform fewer repetitions but still achieve the same mechanical load on the target muscle fibers.

If we are still experiencing central nervous system exhaustion at the time of performing the next training session, then this impairs the hypertrophy stimulus. If we cannot fully activate a muscle during exercise, then we are not stimulating the high threshold motor units, which means that we are failing to produce sufficient mechanical stress on the muscle fibers controlled by these motor units - and this will reduce the amount of hypertrophy results.

In practice, central nervous system exhaustion is caused by either aerobic exercise or muscle-damaging strength training performed in close temporal proximity to the training session.

If we are still suffering from muscle damage at the time of the subsequent training session, then this will affect the hypertrophy stimulus for two reasons. Firstly, this may affect the hypertrophy stimulus to the extent that it causes central nervous system exhaustion. Secondly, this scenario can lead to oxidative stress that interferes with the increase in muscle protein synthesis rate that is stimulated as a result of the anabolic signals elicited by the mechanical load. For this reason, even if we are able to fully activate the muscle, muscle damage can impair hypertrophy by interfering with the signaling process.

What determines the training frequency?

The training frequency is determined by the following factors;

The duration for which the myofibrillar protein synthesis rate is increased after exercise.
The length of time during which muscle damage affects the hypertrophy stimulus of the subsequent training session either by generating central nervous system exhaustion (and thus preventing the recruitment of high threshold motor units) or by increasing oxidative stress.

At this stage, it is unclear how long myofibrillar protein synthesis rates are elevated after exercise, but it is likely to be less than 48 hours. How much shorter than 48 hours is not yet known. If we were to ignore muscle damage as a factor, then the optimal training frequency would be once every 2 days or three times a week. If myofibrillar protein synthesis is only significantly increased for 24 hours after training (which is quite possible), then the optimal training frequency could be once a day - but only if muscle damage is not taken into account as a factor.

The length of time during which muscle damage can interfere with the hypertrophy stimulus of a second subsequent training session is unclear. When conventional strength training sessions are performed, central nervous system depletion is mild and short-lived.

However, higher-volume training (4) and unaccustomed purely eccentric training can impair muscle activation for 2 to 3 days by inducing a greater amount of muscle damage. The duration of the effects of muscle damage-induced oxidative stress on the hypertrophy stimulus lasts 8 to 24 hours in rodents and might be expected to be longer in humans, although exact values have not yet been determined.

For this reason, it seems likely that key volume plays a key role in determining optimal training frequency. High volume requires a longer recovery time, leading to an optimal training frequency of once every 2 to 3 days (depending on whether the exerciser is accustomed to the training and taking into account that the duration of the effects of increased oxidative stress is not yet known).

Moderate volume training sessions could be limited only by the length of time during which the myofibrillar protein synthesis rate is increased (again, taking into account that the duration of the effects of increased oxidative stress are not yet known).

How important is muscle damage?

When it comes to bodybuilding, the issue of training volume is far less controversial than the issue of training frequency.

Most experts agree with the conclusions of the scientific literature, which reports a dose-dependent relationship between training volume and hypertrophy, with the number of sets ranging from 10 sets per week in untrained and trained individuals.Interestingly, the data in these studies refer to weekly training volume, even though these studies compare different training volumes by changing the number of sets performed per training session while keeping the number of training sessions the same. In fact, many experts refer exclusively to the weekly training volume without considering the volume of training sessions.

Nevertheless, at least in untrained individuals, increasing the weekly training volume by increasing the number of training sessions completed does not appear to have the same dose-dependent effect as increasing the weekly training volume by increasing the number of sets performed per training session.

In one study, researchers found that performing the same training session two, three or five times a week produced similar muscle growth (5). Each training session included 3 sets of leg extensions to muscle failure, which meant that the 3 groups performed 6, 9 or 15 sets per week. It was expected that these differences in weekly training volume would have different effects on hypertrophy, but this was not the case. The lack of differences between the groups suggests that muscle damage induced during some of these training sessions may have affected the hypertrophy stimulus during subsequent training sessions, either through reduced muscle activation or increased oxidative stress.

This effect would certainly be less in trained individuals, but despite habituation to repetitive efforts, muscle damage also occurs in trained individuals, and this is particularly true for the upper body muscles (6).

All in all, this shows once again that training volume only counts if it stimulates. When training too often, training volume may not stimulate if the recruitment of motor units is impaired by central nervous system fatigue due to muscle damage or if an increase in the rate of muscle protein synthesis despite anabolic signals is prevented by oxidative stress due to muscle damage.

Why not train less often?

If training too frequently carries the risk of performing workouts that do not stimulate muscle hypertrophy, then the question arises as to whether it would not make sense to train less often and train each muscle only once a week, as many bodybuilders do.

However, there are two reasons why we should train a muscle more often than once a week:

Some people find performing the entire weekly training volume for a muscle group during a single training session too demanding due to the high degree of peripheral fatigue during the training session and severe muscle damage, as well as severe muscle soreness after the workout. This is a matter of personal preference, but it is easy to understand.
There is probably a non-linear dose-response curve of training volume for a given training session. Studies have shown that performing 10 sets of 10 repetitions per exercise is as effective as performing half the number of sets. In addition, the increase in the rate of muscle protein synthesis after training also reaches a plateau at a certain number of sets, meaning that beyond a certain point, more sets will not lead to any further increase in muscle protein synthesis. Once a certain threshold of training volume is reached, splitting the training volume into two training sessions per week should produce greater muscle growth than one weekly training session with the entire weekly volume.

The optimal training frequency therefore depends on the volume performed during the training session. Each training session causes a certain amount of muscle damage, which will determine how often that training session can be performed. However, each training session will only cause a dose-dependent hypertrophy response to the volume performed up to a certain point. For this reason, some training frequencies (in conjunction with the appropriate optimal volume of training sessions) will produce better results than others.

What about psychological stress?

Some research has shown that people who are exposed to high levels of psychological stress take longer to recover after a training session. Although this seems to imply a mechanism involving the central nervous system, it is more likely that this effect is related to reduced recovery from muscle damage. Indeed, several studies have shown that wound healing is slower in different contexts where individuals are exposed to high levels of long-term physiological stress (7,8).

It doesn't take much imagination to see how the repair of muscle damage could be similarly affected by psychological stress.

What does this mean in practice?

The questions considered so far have several practical implications.

First, it is clear that it is possible to train too often, which is mainly related to the effects of muscle damage incurred during one training session on the hypertrophy stimulus of subsequent training sessions.

Secondly, the amount of muscle damage varies from individual to individual (especially due to training status, but also due to stress levels), from muscle to muscle and from training session to training session (especially due to volume). For this reason, the optimal training frequency differs from person to person, from muscle to muscle and from training session to training session. Trying to find the perfect training frequency that will always work for everyone is therefore a doomed endeavor.

Thirdly, we cannot calculate our weekly training volume simply by adding up all the sets performed within a week until muscle failure (or until a certain point before reaching muscle failure), regardless of when they are performed. If training sessions are performed too close together, the stimulus of the subsequent training session will be impaired. How long the interval should be depends on the individual, the muscle being trained and the training session.

In practice, this means that we should start a new training program with a conservative training frequency and increase this frequency until we stop making progress from one training session to the next. In most cases, this will probably mean that we will start with 1 to 2 training sessions for one muscle group per week, depending on the planned training volume.

Conclusion

The training frequency is determined by:

The duration for which myofibrillar muscle protein synthesis is increased after training.
The length of time during which muscle damage impairs the hypertrophy stimulus of the following training session (either through central nervous system fatigue preventing the recruitment of high threshold motor units or through increased oxidative stress).

The amount of muscle damage can vary from person to person, from muscle to muscle and depending on the type of training session. Training sessions with a higher volume produce more muscle damage and therefore require longer recovery. For these reasons, the optimal training frequency varies from individual to individual, from muscle to muscle and depending on the type of training session.

References:

Source: https://medium.com/@SandCResearch/what-determines-training-frequency-62ec783f908f

By Chris Beardsley

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