Why does research tell us that load periodization works?
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Periodization can be defined in practice as “the incorporation of non-random, pre-planned, and timetabled variety into a workout program.”
While this variety can be implemented by periodizing almost any training variable (such as exercise selection, rest period duration, or tempo), it is the periodization of relative load (percentage of 1RM) that has been investigated most often by researchers. Load periodization is where the relative load used in a workout is changed, either from one workout to the next, or from one week or block of training to the next.
Much of the research shows that load periodization produces greater gains in maximum concentric strength (1RM). Also, there seems to be a slight benefit of daily-undulating periodization methods over the traditional linear and reverse linear methods.
Unfortunately, as the research stands at the moment, we still do not know whether it is the variability itself that produces the superior effect of load periodized training programs on changes in 1RM, or the non-random, pre-planned, and timetabled sequence.
This is because the control groups in these load periodization studies have used a constant relative load in all workouts, which removes not only the effect of variety, but also the non-random, pre-planned, and timetabled aspects of variety.
Even so, many critics of the load periodization literature attribute the benefits of periodization to the simple effect of variety.
Indeed, since greater variation is often associated with better performances, while reduced variation has been linked to worse performances (as well as an increased risk of overtraining and illness), it does seem likely that variety is the most probable cause of the effectiveness of load periodization.
Yet, there may still be other explanations for why we see the results we do in the load periodization literature, besides the beneficial effects of variability, and this is because of inadvertent side-effects caused by the research designs that are used.
#1. Specific strength qualities
The first explanation for why periodized programs produce certain results is the fact that strength is specific.
When we say that strength is specific, it means that strength gains are greatest in those tests that are most similar to those used in training. One of the ways in which strength is specific is percentage of 1RM.
Training with heavy loads (close to 1RM) produces greater gains in 1RM than training with lighter loads (further away from 1RM). Conversely, training with heavy loads (close to 1RM) produces smaller gains in repetition strength (muscular endurance) than training with lighter loads (further away from 1RM).
When using a linear periodization model, the final couple of weeks before a strength test use very heavy loads. And linear periodized models frequently produce greater gains in maximum strength (1RM) than non-periodized programs (which use moderate loads throughout).
In other words, training with heavy loads just before a 1RM test produces better results. Not surprising.
When using a reverse linear periodization model, the final couple of weeks before a strength test use very light loads. Reverse linear periodized models produce larger gains in muscular endurance than comparable non-periodized (and also compared to linear periodized programs), but smaller gains in maximum strength.
Training with high reps and light loads just before a muscular endurance test produces better results. Again, totally expected.
So the fact that strength is specific actually explains quite a lot of the research findings regarding changes in either maximum strength or muscular endurance, and the effects are unrelated to variability.
#2. Training volume over time
When they compare different periodization models, researchers often go to great lengths to ensure that training volume is matched over the course of a program.
However, they cannot easily match training volume over a week.
This means that training volume in linear periodized models is frequently greater than training volume in undulating periodization models for some weeks of the program, but smaller in other weeks.
Since volume probably produces a stimulus for muscular hypertrophy that is threshold-dependent (gains in muscle size increase with increasing training volume to a point, and then plateau), undulating programs may be constantly working on or above this plateau, while linear periodized programs may sometimes be on the plateau, and other times be lower down.
This somewhat unpredictable effect would produce an unreliable tendency for undulating programs to produce greater gains in muscle size, which would translate to slightly greater strength gains, so long as heavy loads were also regularly performed as part of the program.
And that is basically what some researchers have found.
#3. Inter-individual responsiveness to load
One fascinating aspect of the principle of individuality that was recently discovered by researchers is that some people achieve greater increases in a range of athletic performance measures when training with lighter loads, while others achieve greater increases in the same athletic performance measures when training with heavier loads.
While we still do not know whether these effects would also occur when testing changes in maximum strength, it seems quite feasible. But, if this occurred, then it could have quite a big effect on the outcomes reported by the periodization literature.
To understand how this effect might play out, let’s first assume that there are two groups in any given study. Also, in the absence of any data to help us, let’s assume that each group comprises 50% subjects who respond best to heavy loads, and 50% subjects who respond best to light loads.
A common study design is to compare one group doing linear load periodization (moving from light to moderate to heavy loads over several weeks) with a daily-undulating periodization group lifting light, moderate, and heavy loads every week.
In this situation, each of the subjects in the linear load periodization group would get a chance to train with an optimal load for every workout in a week for at least one third of the weeks in the program, but would train with a sub-optimal load for the remainder of the weeks. In contrast, each of the subjects in the daily-undulating periodization group would train with an optimal load at least once per week for the whole time.
This would almost certainly lead to use observing a beneficial effect of daily-undulating periodization over linear periodization for increasing maximum strength, which is exactly what tends to happen.
Importantly, however, this beneficial effect of daily-undulating load periodization would only be real at the group level. It would not tell us that daily-undulating load periodization is better than linear periodization for any given individual.
What is the takeaway?
While many researchers are now attributing the effects of load periodization to simple variety, there are other factors that could also explain some of the results we observe in the literature.
Specificity of strength gains can likely explain the superior effects of linear periodization on maximum strength, as well as the superior effects of reverse linear periodization on muscular endurance. Moreover, the proximity of training volume to the muscle growth plateau, and inter-individual variability in responsiveness to load, can likely together explain why daily-undulating periodization groups often achieve superior effects compared to groups doing traditional linear and reverse linear programs.
Ultimately, none of these factors are relevant to an individual who is deciding whether to use a particular periodization method, since they are unrelated to the incorporation of non-random, pre-planned, and timetabled variety into a workout program.
If you enjoyed this article, you will like my first book (see on Amazon).
