Why is progressive overload essential for hypertrophy?

Along with specificity, individuality, and variety, progressive overload is one of the four key strength and conditioning principles.

We use these principles when writing strength training programs to prepare athletes for sport, but they also provide the foundations of all training programs, for any goal.

When designing a training program for increasing muscle size, the principle of specificity helps us determine which exercises we can choose from when trying to develop each muscle group to its maximum potential. The principle of individuality helps us decide which of those exercises to select, how to allocate volume, and how many workouts to do for each muscle each week. And the principle of variety makes sure that we continue progressing, and do not get stuck on a plateau.

In contrast, the principle of progressive overload is less important for hypertrophy at the planning stage, but is more important in each workout, making it absolutely essential for achieving meaningful muscle growth long-term. This is because the presence (or absence) of progressive overload affects the mechanical loading stimulus that leads to hypertrophy.

To understand progressive overload, we first need to understand how gains in maximum strength happen.


How do gains in maximum strength happen?

The ability to lift an extremely heavy object depends on our ability to exert force while muscle fibers are shortening slowly, and is commonly called “maximum strength.”

Gains in maximum strength after a workout involving lifting heavy weights are achieved through four adaptations in addition to improved coordination:

  1. Increases in muscle fiber size.
  2. Increases in the ability of each muscle fiber to produce force relative to its size, probably because of enhanced capacity to transmit force laterally between the muscle fiber and its surrounding collagen layer.
  3. Increases in the number of muscle fibers that are activated, because of an enhanced capacity to reach full motor unit recruitment (this contributes to an increase in the ability of the whole muscle to produce force relative to its size), and
  4. Increases in tendon stiffness.

Increases in muscle fiber size are triggered by a workout when individual muscle fibers belonging to the high-threshold motor units experience high levels of mechanical tension.

Increases in muscle fiber strength relative to size, increases in the capacity to reach full motor unit recruitment, and increases in tendon stiffness seem to be triggered by a workout only if the *whole muscle* (and not just the muscle fibers belonging to high-threshold motor units) experiences very high levels of mechanical tension.

Once these adaptations have occurred, and once we have recovered from the workout, our maximum strength increases. This gives us the ability to lift a heavier maximum weight in a subsequent workout.


What is progressive overload?

Progressive overload is basically the way in which we take the adaptations resulting from a previous workout into account, when performing subsequent workouts.

After a workout in which we lift heavy weights, all of the various adaptations that contribute to gains in maximum strength are stimulated. After workouts involving light or moderate weights, it is likely that only increases in muscle fiber size are stimulated (this is why lifting heavy weights leads to greater gains in maximum strength than lifting either light or moderate weights).

Either way, when we come to perform the next workout, we are stronger.

This means that, in the next workout, we have the option of making progress. If we choose this option, we can either lift a slightly heavier weight for the same number of reps, or the same weight for a larger number of reps.


How does progressive overload affect hypertrophy?

When we perform a typical bodybuilding workout involving a sufficient volume of stimulating reps, we trigger an increase in muscle fiber size. And if we use heavy loads in the workout, we also trigger other adaptations, which improve the ability of the fibers to produce force relative to their size.

Stimulating reps are those that involve the muscle fibers controlled by high-threshold motor units shortening slowly. This state occurs when the muscle exerts a high force, such as when lifting a heavy weight, and when the muscle exerts a maximal force under fatiguing conditions, such as when lifting light or moderate weights within five reps of muscular failure.

When we come to perform our next workout, the increase in muscle fiber size that we have achieved allows our muscles to produce the same force while recruiting fewer motor units.

This means that doing the exact same workout (sets x reps x weight) as before will not involve the same number of stimulating reps. To achieve the same number of stimulating reps, we need to increase either the number of reps with the same weight, or we need to increase the weight.


How does progressive overload affect hypertrophy? (worked example)

If we do a workout of 3 sets of 5 reps to failure with the bench press using 90kg, then that workout will provide 15 stimulating reps, which will lead to some hypertrophy.

However, if we do the same workout of 3 sets of 5 reps with the bench press using 90kg a few days later, after we have fully recovered, then this workout will not provide 15 stimulating reps, because we are not training to failure on all sets. More likely, we will be working at one repetition in reserve on one or two of the sets. This workout would therefore produce a smaller increase in muscle size.

If we continued to do further workouts of 3 sets of 5 reps with the bench press using 90kg, then each sequential workout would involve a smaller number of stimulating reps, and this would lead to smaller and smaller amounts of muscle growth. Eventually, the stimulating effect would be too small for any muscle growth to occur.

In contrast, if we do workouts with progressive overload, either by increasing the weight slightly, or by increasing the number of reps, then the number of stimulating reps remains the same in each workout, and we continue to experience muscle growth. This is why progressive overload is such a key concept for bodybuilding, and why ignoring it will ultimately lead to lifters stagnating and not making progress.


How else can progressive overload help us in practice?

After a strength training workout, our strength is reduced for a short period of time because of transitory changes in three factors: (1) peripheral fatigue, (2) central fatigue, and (3) muscle damage. The effects of peripheral fatigue are quite short-lived, and disappear soon after the workout. Central fatigue that arises during the workout is also very short-lived, and dissipates very quickly. However, muscle damage can take a much longer time to recover from, and may still be present for several days after the workout.

Importantly, this muscle damage can lead to central fatigue developing after the workout. And if this central fatigue is still present at the point when we perform the next workout for the same muscle group, we will not recruit our high-threshold motor units in that workout, and this will lead to a reduced hypertrophic stimulus. For this reason, it is very important that we are able to tell whether we have recovered from our last workout or not.

If we are accustomed to a particular workout, and it does not involve excessive training volume that causes a lot of muscle damage, then full recovery of both muscle damage and central fatigue should occur within 48 hours, which allows us to train a muscle 2–3 times per week in a fully-recovered state. Therefore, if the previous workout was effective for hypertrophy (and we are not in an adverse state), then we should be able to increase our performance in an exercise by at least one rep, or by a small amount of added weight.

If we are unable to improve our performance by either one rep or by a small amount of added weight, then it is likely that either: (1) we are in an adverse state because of high stress levels, inadequate food intake, or a lack of sleep, or (2) the recovery time from our previous workout has increased, because we changed an exercise or did a larger amount of volume, or (3) the previous workout did not stimulate muscle growth.

We can use this process to decide how to move forwards, when we plateau.

Firstly, we can check whether we are in an adverse state. If we are, we can fix this, and then our progress should resume as before. Secondly, we can check to whether our recovery time has increased, by reducing our training frequency slightly. If our recovery time has increased, then this should then allow us to resume progress as before. Thirdly, if neither of these tactics help, then we must assume that our current workout is not working for producing muscle growth, and we either need to change the exercise, or increase the volume by one set.

If we do not follow a program that involves obvious progressive overload, then we do not have this tool available to us. We essentially have to guess whether we are building muscle or not.


What happens with programs that are periodized?

If we work with the same rep ranges, rather than following a (linear, reverse linear or block) load periodization model, then progressive overload provides us with a very clear, external indicator that we are gaining muscle over time.

However, if we use load periodization, and alter the repetition range that we are using from one workout to the next (daily undulating periodization), from one week to the next (weekly undulating periodization or traditional linear periodization), this can obscure whether progressive overload is happening, because it does not allow us to compare the weight or reps from every workout to the next one.

Therefore, we cannot really tell whether we are gaining muscle from one workout to the next. We have to wait until the end of the program, when we test our strength against baseline. While there are advantages of load periodization, this is one major disadvantage.


What is the takeaway?

The principle of progressive overload is essential for achieving meaningful amounts of muscle growth long-term, because it affects the size of the mechanical loading stimulus in each set that leads to hypertrophy.

If we do the same number of sets and reps with the same weight for multiple workouts, then each sequential workout will necessarily involve a smaller number of stimulating reps, and this will trigger smaller and smaller amounts of muscle growth. Eventually, the stimulating effect will be too small for any muscle growth to occur. In contrast, if we do workouts with progressive overload, either by increasing the weight slightly, or by increasing the number of reps, then the number of stimulating reps remains the same in each workout, and we continue to experience muscle growth (up to a point).

Additionally, progressive overload can function as a valuable external indicator of whether we are gaining muscle over time. However, this only really works if we either do not use load periodization.