A First-Principles Approach to Hypertrophy

Hypertrophy is a hot topic nowadays. The fitness industry seems to
generally distinguish “hypertrophy” training from strength
training, and there are receipts everywhere on how to specialize your
training for one or the other. There is a fair amount of
peer-reviewed research on the topic, and most theories and claims are
based on the findings of these works.

However, there seems to
be an alarming lack of deductive reasoning: conclusions have to
follow logically from premises. If the findings in this or that
experimental study are at odds with deductive reasoning from basic
principles, something is not adding up. The prevailing methodology is
taking these experimental studies at face value, and leaving
deductive reasoning aside, as well as the observations of coaches and
trainees for a hundred years. The aim of this article is not to argue
the validity or shortcomings of the scientific fitness literature,
but to provide the basic principle-based deductive reasoning
regarding hypertrophy and how to train for it.

The topic of
hypertrophy has been addressed in a few articles on this site, and
what I will argue here is in line with what has been recently
discussed at length in Starting Strength Radio episodes #219 and #240 (Hypertrophy and You’re Not Doing Hypertrophy, respectively on the Starting Strength Network or listen here). I will start by
reviewing what the main function of the muscle is, what hypertrophy
is, and how it relates to this primary function, and then I will show
how the General Adaptation Syndrome allows us to recognize
hypertrophy as a physiological adaptation and helps us to understand
how to train for it.

The
Primary Function of Skeletal Muscle

The main function of
skeletal muscle is to move and stabilize the human body. It does so
by applying force to the system of levers that is the skeletal
system. To understand this, we need to know what “force” and
“lever” are.

Force is an influence
that causes an object to change its velocity: to accelerate. Its
value is given by multiplying the mass of the object times its
acceleration. A lever is a rigid body which is capable of rotating on
a point on itself, called a fulcrum. Think about two kids playing on a
seesaw for a simple example of how external forces interact with a
lever: the force of gravity acts on the first kid, the heavier one,
making the seesaw rotate around the fulcrum and lifting the second
kid up. The longer the distance between the heavier kid and the
fulcrum, the least force needed (the less the heavier kid has to
weigh) to move the second kid up.

In order to apply
motion to the skeletal system, the muscle contracts – shortens –
and applies force by pulling on the tendon, which transfers this
force and pulls on the given bone at its attachment point. Rotation
follows around the given joint. In mechanical terms, the bone is the
lever and the joint the fulcrum. Think about the biceps and forearm:
force is applied by the biceps at the attachment point of the tendon
on the forearm, the forearm rotates around the elbow (fulcrum), and a
resistance located at the hand – a dumbbell for example – is
accelerated. The ability to apply force to an external resistance by
our musculoskeletal system is what we call strength.

The main function of
the muscle is then to generate force by contracting. Force is the
physical quantity that measures the action of the muscle on the
tendon’s attachment to the bone. Force production has to be sustained
through varying periods of time, which requires metabolic processes
in the muscle to generate and consume ATP (adenosine triphosphate,
the molecule that is used as “fuel” for muscle contractions).
These metabolic processes are the support for the muscle to perform
its primary function, acting as energy supply so that it can contract
and produce force against the skeleton.

Muscular
Hypertrophy and Strength

Hypertrophy is an increase in muscle size. More specifically, when we
talk about hypertrophy we are discussing an increase in the
cross-sectional area (CSA) of the muscle. Muscles are constituted of
thousands of muscle cells (muscle fibers). Within a simplified model,
muscle fibers are made of two main components, sarcoplasm and
myofibrils. The sarcoplasm surrounds the myofibrils and contains
ions, small diffusive molecules, mitochondria, and other organelles.
The myofibrils consist of long chains of myofilaments made of
proteins, in particular actin and myosin. These proteins are
responsible for muscle contraction: pairs of myofilaments form cross
bridges that draw the protein filaments past each other, shortening
the myofibrils and contracting the muscle fiber.

Myofibrils are then
mechanically responsible for muscle contraction and force production,
while the sarcoplasm has other functions, including hosting most of
the metabolic processes of the muscle. If it is to increase its force
production capacity, the muscle needs to increase the number of
myofilaments so that stronger contractions can occur. This means
higher numbers of larger myofibrils, and increased sarcoplasm for
metabolic and other processes to support the increased contractile
potential. As a result, the muscle CSA increases, and hypertrophy
occurs.

It is a structural
change to the muscle fiber, a persistent transformation that can be
accumulated over long periods of time. Note that we are not concerned
here with transient increases in muscle CSA related to the
accumulation of metabolites, lactate, etc. in the sarcoplasm.
Everybody is familiar with “the pump,” which happens when some of
this takes place and lasts for a few hours, but there is some
evidence that there may well be transient increases in muscle CSA due
to training (especially from high volume workouts) that could last
days or even a week or two. These changes won’t accumulate over
time in the way structural changes do.

It is clear then that
increased force production requires larger muscles, but is it at all
possible to produce long term muscular hypertrophy in the absence of
an improved ability to produce force? According to our model of the
muscle fiber, this would basically mean long-term sarcoplasmic
hypertrophy in the absence of myofibrilar hypertrophy. The fact is
that there is absolutely no evidence of this happening, and most
probably never will be. Why would our bodies promote an increase
in muscle size in the absence of improved strength? It makes no
sense, bigger muscles are heavier and require more force to be moved
around, and this wouldn’t be efficient at all. Natural selection is
cleverer than that.

Besides, anecdotal
evidence doesn’t support it. We all know that athletes in more
strength demanding sports are bigger, and athletes in more metabolic
demanding sports, which require less force production capacity, are
smaller. Powerlifters and strongmen have huge muscles, sprinters or
crossfitters have big but not huge muscles, and marathoners have
small muscles. We all know that bigger people are generally stronger
than smaller people. And we also, crucially, know that a bigger, more
muscular version of you is stronger than a smaller version of you.  

Hypertrophy is therefore the mechanism by which muscles increase
their force production capacity.

General
Adaptation Syndrome

We have established
what hypertrophy is, but what makes it happen? For this we need to
understand the General Adaptation Syndrome: a model that explains how
living systems react and adapt to the environment. The environment
is, in this context, a series of physical perturbations that act upon
us and produce a response from our bodies that we call stress.
This is one of the things our DNA is for: if we are able to recover
from this stress, physiological adaptations occur so that the same
stressor no longer represents as big a recovery challenge – in its
historical context, a threat to our lives. (Stress, recovery,
adaptation (SRA) – It’s Time to Stop Talking About “Supercompensation”)

Environments change all
the time, and always have. Without this mechanism, we wouldn’t be
able to adapt to the changing environment and we would die very
quickly. A nice example of the SRA cycle is the process by which we
get a suntan (The Biggest Training Fallacy of All). The
stressor is the ultraviolet (UV) radiation in the light coming from
the sun, which produces a stress in our bodies to which we adapt and
get tanned. Melanin is produced and our skin darkens, such that next
time we can withstand the same volume of UV radiation without it
representing a challenging stress.

A very important characteristic of the SRA process is that the stress
has to be specific to the adaptation. In order to get a suntan we
need to be exposed specifically to UV radiation (any other type won’t
work) of sufficiently duration relative to our current level of
adaptation, or the stress would not represent a challenge and the
adaptation would not be necessary. If you stay in the shade, the
solar radiation reaching your skin won’t be of high enough
intensity and you won’t get tanned. The important piece of this
process is the dosage of the stress, which has to be enough to
produce the adaptation but not so much that you can’t recover. The
stress in the SRA must be capable of being recovered from.

Hypertrophy
as a Strength Adaptation

We have now the tools
and ingredients to view hypertrophy in a slightly different light:
hypertrophy is nothing but a physiological adaptation. But what is
the stress that produces this adaptation? If hypertrophy is the
mechanism by which the muscles increase their force production
capacity, and the stress has to be specific to the adaptation, then
it is clear that the stressor required to produce a hypertrophy
adaptation must be something that challenges the ability of the
muscle to produce force.

The limiting factor
must be your strength, otherwise the stress would not represent a
challenge for the actual force production capacity of the muscle,
and, like when you tried to get a tan, the adaptation would not be
necessary if you were already tanned. We could talk about strength
and hypertrophy interchangeably: strength is the functional
consequence of muscular hypertrophy, hypertrophy is the physiological
adaptation from displaying strength as a stressor for the muscle.

Since hypertrophy and
strength are sides of the same coin, the most efficient way to train
for hypertrophy is also the most efficient way to train for strength
(Bodyparts vs. Movement Patterns).
This is big, basic compound movements that work the body in a functional way: squat, presses,
deadlift, chins (see Practical Programming for Strength Training, 3rd edition, Mark Rippetoe and Andy Baker, and A New Definition for Strength Training).
The phenomenology is quite clear: when you train for strength and get
stronger, you also get bigger.

Following logically
from our premises, we can infer that performing a heavy single in any
of these exercises is theoretically the most specific stressor to the
hypertrophy adaptation: it is the most force production-limited
stress one can have. But is it enough stress? Lying down in the sun
when it is high up in the sky is the most specific stress to get a
tan, but if you do it for just two minutes will you get tanned? A
heavy set of 5 reps may still be specific enough for hypertrophy –
lots of force production required.

Will a set of 10, or
20, or whatever large number be specific enough? These events require
less and less force production the further they are from a heavy
single, so the higher the number of reps, the less specific and less
optimal the stress for the desired hypertrophy adaptation. If instead
of lying down in the sun you stayed in the shade, even if you stayed
there for the whole day, you wouldn’t have got tanned, as the
intensity of UV radiation reaching your skin would have been too low.
Lying down in the shade for the whole day is the equivalent to a set
of 40000 reps; this is the equivalent of running a marathon, no tan
and no hypertrophy at all.

Is training based on
heavy singles then the best for hypertrophy/strength? Experience
tells us that, for most people, a heavy single is not stressful
enough to force an adaptation. We would need to do multiple, lighter
by necessity, singles, to accumulate enough stress. This is not
practical for several reasons: first, a heavy single depends heavily
on skill, this immediately rules out this type of training for
novices. Second, novices and intermediates need exposure to multiple
reps per set in order to obtain or maintain proper technique, and for
the coach to be able to correct the movement in real time. And third,
if you need to do 10 singles to produce enough stress, with rest in
between, that would be too time consuming for most. Besides, we may
well benefit from other physiological adaptations while we train for
hypertrophy-strength. In particular, metabolic and cardiorespiratory
adaptations that better occur when doing sets of multiple reps.

And here comes the experience of countless coaches and trainees over
a long period of time all over the world: sets of 5 is what works
best for strength and therefore hypertrophy, for most people (see Fives Build Muscle Better and 5s, Not 10s). A range between 3
and 6 reps, depending on individual characteristics and training
advancement, may still be optimal. Experience tells us that a heavy
set of 5 is still specific enough to produce the desired hypertrophy
adaptation, and the amount of stress is the optimum. If needed, we
can use a few sets across.

The heavy set of 5 is
the equivalent, when we got tanned, of using the correct intensity of
UV radiation for the correct amount of time. The set of 5 for
hypertrophy is the sweet spot when we take into account the
specificity of the stress to the adaptation, the dosage of stress
needed, and the practical aspects of training.

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