Updated: May 2, 2022
When looking at physiological adaptations to strength training, we distinguish between two main effects: neural and structural.
Neural adaptations describe how our nervous system becomes more efficient at recruiting a higher number of so-called high-threshold motor units (the ones which are great at lifting heavy weights and moving explosively), as well as recruiting those fibers at a greater frequency. In short: MORE recruitment of those fibers QUICKER.
The second main component of strength increases are structural. This means, the diameter of our muscle fibers gets bigger - a process also known as HYPERTROPHY. A bigger muscle has a greater cross-sectional area that can produce more force at a given time.
The following study attempted to answer the question "At what time points in our training are those two main components of strength adaptation expressed?"
57 healthy, untrained men were recruited for the study. One part of the group performed resistance training for 12 weeks, one group for four years, and one group did not perform any exercise and acted as the control group.
Cutting to the chase: In the first 12 weeks of resistance training, NEURAL adaptations were the predominant factor for strength gains in subjects, wherease STRUCTURAL changes played a greater role for improvements in strength thereafter.
This has the following implications for our strength training practice:
1 Why do neural adaptations happen first? I would argue that it is the body's survival mechanism to perform tasks successfully first while maintaining integrity. This means that in the beginning, the body is more worried about how to coordinate the activation of different muscles, how to perform different parts of a movement, how to learn a technique efficiently. These are all NEURAL factors of adaptation as our nervous system tries to coordinate the work of muscles, connective tissue, skeleton, as well as brain performance. As such, the body doesn't require high levels of muscle mass to perform "survival actions" in the first place.
2 Knowing that neural adaptations happen predominantly EARLY in our strength journey, it is a realistic goal to not expect high degress of muscle mass increases in this phase. Once the movement techniques reach a high level of proficiency, structural adaptions kick in, as now the body doesn't have to worry so much about learning techniques anymore.
3 It appears that, to maximize strength, increases in muscle mass become more important once the lifter progresses beyond a certain timeline. As such, nutritional interventions (e.g. eating a caloric surplus), as well as manipulating training variables (e.g. planning phases of variation in training volume and load) reach greater importance. Overall, the complexity of training increases the further the lifter progresses.
In a nutshell: visible muscular changes to one's physique only start happening efficiently beyond a minimum of 12 weeks of strength training.
The stronger the lifter becomes and the greater his training experience, training needs to be manipulated to increase muscle mass in oder to maximize strength gains.