Even though some people may argue that bigger muscles leads to a greater potential for increased strength, optimising muscle size and optimising muscle strength are two different things.
How Muscles Work
Muscle tissue consists of two types of muscle fibers (note we are avoiding muscle fibers subtypes):
Type I Muscle Fiber. Also known as slow-twitch fibers, type I muscle fibers use oxygen more efficiently and can be used over longer periods of time; think endurance. These have little potential for hypertrophy.
Type II Muscle Fiber. This is the fast twitch type of muscle fiber that can burn energy quickly for short bursts of strength. These are our larger, more powerful muscle fibers that have a great potential for hypertrophy. The two most commonly discussed types of type II muscle fiber are type IIa (fast oxidative glycolytic) and type IIb (fast glycolytic).
This leads us to the Size Principle of Motor Unit Recruitment. One motor unit is a nerve and the muscle fibers to which it is attached.
The Size Principle states that when the central nervous system recruits motor units for muscle contraction, it begins with the smallest, weakest, more easily excited type I motor units first and progresses to the larger, stronger, more-difficult-to-excite type II motor units only when force needs to be maintained or increased.
In other words, a light weight will only stimulate smaller motor units. A heavy one will activate more powerful type II motor units.
1. Maximal weight
To get stronger we need to activate all of the motor units, so the standard recommendation for load is >85% 1 RM.
2. Fewer reps
Think about it: your one repetition maximum literally means that most weight you can lift one time so, generally speaking, if you are able to lift a resistance more than six times in a row, it is not heavy enough to stimulate your highest threshold motor units. A word of caution: working near maximal lifting (>85% 1 RM) can be dangerous for a novice lifter.
3. The rest interval
Generally two to five minutes rest is the interval recommendation… This can be related to our understanding of the metabolic pathways, specifically regeneration of adenosine triphosphate and creatine, but that can get a little complicated.
An easier way to explain it is that the central nervous system needs full recovery in between sets. It is also important to consider that the stronger an individual is, the more rest he or she will likely need between sets when working with a near maximal resistance.
At this point it would be easy to think that lifting heavy weights makes a person stronger, but is this also the best strategy for getting bigger muscles?
The quick answer is no. Here’s why:
1. Protein degradation
Resistance training initiates protein degradation, the breakdown of muscle tissue. This creates the right conditions for rebuilding bigger muscles during rest and recovery periods.
The amount of protein degradation that occurs depends on how we approach our training. Obviously, the extent to which our muscle rebuilds depends on the quality of our post training recovery (an issue separate from the discussion taking place in this article).
Protein breakdown is stimulated by two different factors:
- The amount of weight lifted. Heavier weights lead to greater degradation per rep.
- The number of reps. Consecutive repetitions further contribute to degradation.
2. Heavier weights, higher reps
To make our muscles bigger, we need to use a weight that is not only heavier, but also one that we can lift for a high number of reps. The load and rep recommendation of 67%-85% 1 RM for 6-12 reps is the starting guideline for muscle hypertrophy.
This load/rep ratio satisfies the two factors that stimulate protein degradation: heavy weight, high rep scheme, so that you get maximum muscle building during recovery.
3. And…the rest interval
The rest interval recommendation for hypertrophy is 30 to 90 seconds. Why less recovery time than for increasing muscle strength?
One reason is that studies have shown this rest interval range leads to elevated levels of serum growth hormone during exercise. Growth hormone is important in stimulating muscle growth, hence the resulting hypertrophy.
Now you can see that there is a reason that most fitness textbooks will give you this set of recommendations for hypertrophy and strength. They act like building blocks, a starting point.
As PT Coaches, we can use this starting point to develop individualised programs for each client.
The recommendations described don’t take into account key variables such as training frequency, training experience, mode of exercise, total number of exercises per muscle group, client somatotype, supplementation, nutritional intake, or recovery quality. Furthermore, programming ideologies such as supersets, drop sets, compound sets, half reps, negatives, periodisation format, and others play a significant role in the type and rate of adaptation that occurs.
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[Adapted from an article by the International Sport Sciences Association and it’s textbook]