Hypertrophy describes specifically the enlargement of the fibers that make up skeletal muscles
Definition
The enlargement of an organ or tissue from the increase in size of its cells. (Oxford dictionary)
Hypertrophy is usually used in reference to the enlargement of skeletal muscle due to exercise.
Hypertrophy describes specifically the enlargement of the fibers that make up skeletal muscles only. It is not a description of strength, cardiovascular endurance, or any other performance metric. This means while hypertrophic training will have beneficial effects in those areas, it is not the primary goal of programs constructed towards hypertrophy.
Muscular growth (hypertrophy) is the result of multiple processes that occur during load-bearing exercise.
It can also occur in other circumstances. But I am focusing on weight training programming, so I’ll be referring to that. The tension of muscle fibers during exercise causes microtears in the fibers (myocytes), which in turn causes an inflammatory response. Sarcoplasmic hypertrophy refers to the buildup of cellular fluid that acts as an energy source for the cells. This is different from myofibrillar hypertrophy, which involves the addition of actual motor units to the muscle. The latter is associated with strength increases.
Training implications
As the increase in size of the muscle is an adaptive response to stimuli, this stimulus must continue to increase over time to achieve the same effect. For example, (broadly) once your bicep adapts to lifting 25lbs 10 times by increasing the motor units in the bicep, this load and volume will no longer provide enough resistance or stress to create adaptation. This goes the same for exercises across the board. Continued adaptation requires continued incremental increases in load or volume. These increases either need to exhaust the energy stores of the muscles causing sarcoplasmic hypertrophy or overload the myofibrils to increase motor unit allocation.
Sarcoplasmic hypertrophy
It’s a result of workouts involving longer TUT (time under tension) and shorter rest intervals between sets. Eccentric, high volume, light weight construction with sub-60 second rest periods at a volume of 14-18 sets/muscle/week is a general guideline if your goal is sarcoplasmic hypertrophy. While the primary driver of muscle growth will be from sarcoplasmic fluid increase, strength will also increase inherently due to general mechanical stresses on the muscles.
Myofibrillar hypertrophy
Myofibrillar hypertrophy stems from a more load-intensive focus with longer rest periods. This allow senergy production to catch up to the demands of the sets. Lower volume, high load, low rep range sets for 5-10 sets/muscle/week is preferable for strength gains. The primary goal with this construction is mechanical damage to the muscle which will be repaired with slightly more resources than it had previously. This means the load and stress matters more than the buildup of products of energy production. Therefore, allowing for less sets of more weight with long rest periods (2+ minutes)
While this is not remotely an exhaustive description or list of methods to describe hypertrophic training, it should be helpful in conveying the underlying processes that cause muscular growth. I’ll be diving farther down the hypertrophy rabbit hole in more articles to come.
