Volume and training status

It is generally assumed that more advanced lifters need higher workout volumes to cause hypertrophy. But is this idea actually valid? Let's look at the physiology.

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#1. CNS fatigue increases gradually over a workout

CNS fatigue builds up gradually over the course of any exercise session that involves repeated, intermittent muscular contractions. Indeed, this has been observed during workouts of multiple isometric contractions, for example.

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It has also been observed after workouts involving repeated drop jumps as well. This suggests that is also occurs during normal strength training workouts. Clearly, this will reduce the amount of hypertrophy that is stimulated in the later sets of a workout by reducing the access that we have to the highest high-threshold motor units of any muscle that is being trained.

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#2. Calcium ion-related fatigue increases over a workout

Just like CNS fatigue, calcium ion-related fatigue also builds up over the course of any exercise bout involving repeated, intermittent muscular contractions, and this is especially the case when the contractions involve high efforts, as this activates the more susceptible, fast twitch muscle fibers.

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Calcium ion-related fatigue will necessarily reduce the amount of hypertrophy that is stimulated in the later sets of a workout by reducing the magnitude of mechanical tension that can be generated by the affected muscle fibers. Since the susceptibility of muscle fibers to calcium ion-related fatigue is determined by their oxidative capacity, this will always produce the greatest effect in the muscle fibers of the highest high-threshold motor units.

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#3. Training status probably affects which muscle fibers can still grow

It is very well-known that muscle growth occurs more rapidly in beginners than in intermediate or advanced lifters. However, the exact reasons for this are still not well-established. One possibility is that beginners can stimulate growth in all of the muscle fibers of the high-threshold motor units, while intermediates and advanced lifters are limited to causing growth in a smaller proportion of those same muscle fibers.

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Conclusions

It is generally assumed that advanced lifters need higher workout volumes to cause hypertrophy. But is this true? During any strength training workout, central nervous system (CNS) fatigue builds up gradually. So, the later sets cannot achieve as high levels of motor unit recruitment as the earlier sets. Calcium ion-related fatigue also builds up gradually, preferentially affecting the least oxidative fast twitch fibers of the highest high-threshold motor units. So, the later sets cannot achieve as high levels of mechanical tension in those fast twitch muscle fibers. The progression of these fatigue mechanisms over a workout is one of the reasons why the dose-response of hypertrophy to training volume is not linear (such that 3 sets do not cause 3 times as much hypertrophy as 1 set). Yet, it is also possible that training status affects which muscle fibers in a muscle are capable of growth. It is known that even untrained people cannot cause growth in the muscle fibers of low-threshold motor units, as they have already reached their maximum possible size. Thus, when beginners become intermediates, they could display a reduction in the rate of hypertrophy because the lowest group of high-threshold motor units reaches a plateau in size. When intermediates become advanced, they could similarly reach a plateau in the middle group of high-threshold motor units, leaving them only with the ability to cause growth in the highest group. Since the highest group is the most susceptible to CNS fatigue and calcium ion-related fatigue, it suggests that high volumes are unlikely to be useful for advanced lifters. Finding ways to maximize motor unit recruitment levels is likely to be a far more valuable strategy.