With all the debates about the optimal training frequency, the right amount of training volume, and the best rest period duration to use between sets, it is easy to forget that progressive overload is a key strength and conditioning principle without which meaningful amounts of hypertrophy will not occur over the long-term.
Even so, we can learn a great deal about how strength training works if we consider the reasons why we might fail to make progress from one workout to the next, either by failing to increase the number of reps with a given weight, or by being unable to increase the weight on the bar.
What are the reasons why we may be unable to make progress from one workout to the next?
There are three possible scenarios in which we might find ourselves unable to increase either the number of reps with a given weight or the amount of weight itself from one workout to the next, as follows:
- Inadequate workout stimulus — the previous workout did not cause a big enough stimulus to the high-threshold motor units, with the result that either muscle protein synthesis rates were not elevated for long enough, or that our capacity for motor unit recruitment was not increased, or both. Consequently, no adaptations occurred in either the muscle or the central nervous system, and this resulted in a lack of any strength gains.
- Incomplete recovery— the previous workout caused a stimulus that resulted in adaptations that support strength gains, but it also caused a substantial amount of muscle damage. This muscle damage caused a reduction in the ability of the trained muscle to produce force, which lasted until the next workout was performed (moreover, this muscle damage may or may not have also caused central fatigue to be stimulated, which prevents the recruitment of high-threshold motor units).
- Inadequate stimulus and incomplete recovery — the previous workout did not cause a big enough stimulus to the high-threshold motor units, with the result that no adaptations occurred. However, a substantial muscle damage was still produced, and this caused a reduction in the ability of the trained muscle to exert force, which lasted until the next workout was performed.
It is worth looking carefully at each of these scenarios so that we understand exactly what might be happening inside the body when we fail to make progress from one workout to the next.
#1. Inadequate workout stimulus
When a workout fails to produce a big enough stimulus such that we fail to make progress in our next workout, this will not affect the results of the next workout. Even so, if we do the exact same workout as the previous time, it is unlikely that we will observe a different result the second time around. In theory, we could continue performing the exact same workout indefinitely, without observing any strength or size gains.
#2. Incomplete recovery
When a workout causes so much muscle damage that our capacity to produce force is impaired at the time of the next workout, this can affect the results of the next workout, but only if central fatigue is present.
Central fatigue is often triggered by muscle damage caused by strength training, especially when training volumes are high. When central fatigue is present, this means that the high-threshold motor units within the muscle cannot be recruited, even when we train to muscular failure. As a result, despite training hard, we do not stimulate gains in strength or size.
When central fatigue is *not* present, our ability to produce force is impaired because individual muscle fibers have been weakened by damage. Even so, we are still able to recruit high-threshold motor units. This enables us to produce force with the highly-responsive muscle fibers that are controlled by these motor units, and thereby cause them to experience the mechanical loading that is necessary to stimulate hypertrophy. While the total force experienced by some of these muscle fibers may be reduced due to damage, this will not be the case for all of them. Consequently, progress can still be made.
#3. Inadequate workout stimulus and incomplete recovery
Sometimes, a workout fails to produce a big enough stimulus such that we do not make progress in our next workout, while simultaneously also causing a great deal of muscle damage.
This sounds like a very unusual scenario, but is actually quite a common problem for dedicated lifters to experience.
Indeed, whenever we produce central fatigue that lasts up until the next workout, we are risking bringing this scenario about. We record a lack of progress and we assume that we have failed to produce an adequate workout stimulus the previous time (rather than that we are experiencing incomplete recovery). So we increase our training volume and maybe add some advanced techniques into our workout. This causes even more muscle damage to occur, and this perpetuates our state of central fatigue. Each workout we perform in this state produces no stimulus to the high-threshold motor units because of the presence of central fatigue, but still causes muscle damage.
What does this mean in practice?
In practice, this means that there are two conditions when a strength training workout will produce muscular adaptations: (1) when progressive overload is achieved, and (2) when progressive overload is *not* achieved because of muscle damage without the presence of central fatigue.
Moreover, there are three conditions when a strength training workout will not produce adaptations: (1) when progressive overload is *not* achieved because the stimulus from the last workout was too small, and (2) when progressive overload is *not* achieved because of muscle damage in combination with central fatigue, and (3) when progressive overload is *not* achieved both because the stimulus from the last workout was too small and also because muscle damage is still present.
Consequently, while it is technically possible to achieve muscular adaptations without simultaneously achieving progressive overload from one workout to the next, the easiest way to guarantee that adaptations are occurring is to ensure that progressive overload is also happening. Doing otherwise is a gamble that may or may not pay off, and it is impossible to know whether it is paying off for as long as progressive overload fails to occur.
What does this mean for overreaching and overtraining?
Functional and non-functional overreaching and overtraining are terms that are often used interchangeably but are actually quite different. The definitions of each term are as follows:
- Functional overreaching — a short-term reduction in performance that later leads to improved performance after a taper.
- Non-functional overreaching — a short-term reduction in performance that recovers fully (but does not lead to improved performance), and only after a sustained period of rest.
- Overtraining — a longer-term reduction in performance that recovers fully, but only after a sustained period of rest of longer than 2 months.
Functional and non-functional overreaching are generally regarded as non-pathological states, while overtraining is a pathological condition requiring medical diagnosis. When most lifters talk about overtraining, they are usually referring to non-functional overreaching (unless they have consulted with a physician and received a diagnosis, which is rare).
Fundamentally, however, functional and non-functional overreaching both involve periods of time in which progressive overload fails to occur.
It is therefore possible that functional overreaching happens when we are training in a condition of incomplete recovery such that muscle damage is present from one workout to the next, but the amount of muscle damage is not so severe that central fatigue is being triggered. Therefore, despite the lack of progressive overload, we are still able to make progress.
In contrast, non-functional overreaching may happen when we are training in a condition of incomplete recovery such that muscle damage is present from one workout to the next and the amount of muscle damage is so severe that central fatigue is being triggered. Since we are unable to recruit any of our high-threshold motor units, we do not make progress.
What is the takeaway?
In any given workout, if progressive overload is not achieved, then either the stimulus caused by the previous workout was inadequate or the amount of recovery time was insufficient, or both. When the amount of recovery time is insufficient, this can occur due to either muscle damage or both muscle damage and central fatigue. When central fatigue is present, this prevents adaptations from occurring.
While it is technically possible to achieve muscular adaptations without simultaneously achieving progressive overload from one workout to the next, the easiest way to guarantee that adaptations are occurring is to ensure that progressive overload is also happening.