---
title: 'What is Muscle Hypertrophy? | Physiology and Mechanisms of Muscle Growth in 5 minutes!'
source: 'https://youtube.com/watch?v=TAf5MN9fOjU'
video_id: 'TAf5MN9fOjU'
date: 2026-06-28
duration_sec: 342
---

# What is Muscle Hypertrophy? | Physiology and Mechanisms of Muscle Growth in 5 minutes!

> Source: [What is Muscle Hypertrophy? | Physiology and Mechanisms of Muscle Growth in 5 minutes!](https://youtube.com/watch?v=TAf5MN9fOjU)

## Summary

This video explains the physiology of muscle hypertrophy at the cellular level, from micro trauma caused by training to the role of satellite cells and muscle protein synthesis. It covers the three mechanisms of hypertrophy (mechanical tension, metabolic stress, muscle damage) and distinguishes between myofibrillar and sarcoplasmic hypertrophy.

### Key Points

- **Introduction** [0:00] — Matt from Movement System introduces the topic of muscle hypertrophy and explains the goal of going from a smaller to a bigger bicep.
- **Muscle Fiber Structure** [0:25] — Muscle fibers are composed of myofibrils; satellite cells surround the fibers and are crucial for growth.
- **Three Mechanisms of Micro Trauma** [1:10] — Dr. Schoenfeld's three mechanisms: mechanical tension, metabolic stress, and muscle damage. Training combines these to cause micro trauma.
- **Hormonal Cascade and Satellite Cells** [1:48] — After micro trauma, a hormonal cascade (testosterone, IGF-1, growth hormone) activates satellite cells to initiate muscle protein synthesis.
- **Muscle Protein Synthesis** [2:23] — Satellite cells use DNA to encode amino acids into muscle proteins, filling damaged areas and adding sarcomeres to myofibrils.
- **Hypertrophy vs Hyperplasia** [3:12] — Primary mechanism is hypertrophy (enlarging existing myofibrils), not hyperplasia (creating new ones).
- **Recap of the Hypertrophy Process** [4:23] — Recap: training → micro trauma → hormones/satellite cells → new proteins → bigger myofibrils → bigger muscle.
- **Myofibrillar vs Sarcoplasmic Hypertrophy** [4:54] — Two types: myofibrillar (contractile proteins) and sarcoplasmic (non-contractile proteins). Offers to make follow-up videos.

## Transcript

hey what's up guys it's matt with
movement system today we're going to
talk about what is muscle hypertrophy
so we're going to explain at the muscle
fiber level how we're actually
going from damaging a muscle to muscle
protein synthesis and rebuilding a
muscle in the physiology of that cycle
let's go ahead and dive into it
[Music]
okay so to lay the groundwork our goal
is to go from smaller bicep
to bigger bicep how are we going to do
this well
when we think about the layers of the
muscle fiber we actually have when we
think about the whole muscle when we
look at a cross section of that many
muscle fascicles
and those fascicles with different types
of fibers are made up of
many individual muscle fibers and what
we're looking at here is one muscle
fiber so what you'll see here is that
there are actually many myofibrils
making up this one fiber and then what
you'll see in orange are
satellite cells around the fiber so you
may have heard
that muscle cells are multi-nucleated
and this is actually going to be a
really important
thing to remember when we're thinking
about the process of muscle hypertrophy
okay so step one is to actually go from
a fiber to a fiber
that has had some micro trauma and how
do we do that with training
these are dr schoenfeld's three
mechanisms of muscle hypertrophy
mechanical tension metabolic stress and
muscle damage
so the training that you do and the
training that you program as a strength
coach or as a personal trainer
is going to have some combination of
mechanical tension metabolic stress and
muscle damage
so we can do high rep training that's
going to have more metabolic stress we
can do heavy loaded training it's going
to have more mechanical tension
but either way some combination of these
three
factors are going to actually lead us to
causing micro trauma
at the muscle fiber level so once we've
done training
and we've gone to a muscle fiber that
has some micro trauma
those myofibrils the actin and the
myosin within those myofibrils
have had some structural damage what
we're going to need to do next
is muscle protein synthesis so once
micro trauma has occurred at the
myofibrillar level
we actually have a hormonal cascade of
things like testosterone and igf-1 and
growth hormone
that are going to signal that there's
been damage and
as well activate satellite cells so
these are the satellite cells that we're
talking about here
now this is really important those
satellite cells
are at the level of dna so that dna can
actually encode
transcribe amino acids which can then
become muscle
proteins so these satellite cells with
the nuclei in there
will actually kind of fill in the areas
that have had micro trauma
and they will become through a process
of dna to amino acids to proteins they
will become
the myofibrils and that's really
important because that's actually the
whole principle
of adding sarcomeres and making a muscle
bigger
if this has been helpful for you so far
make sure you go ahead and hit that like
button
and subscribe and turn your
notifications on so whenever i make
follow-up videos about more things
related to muscle hypertrophy and
strength conditioning
you won't miss them okay so just to be
abundantly clear here
if this is a muscle cell and there's
myofibrils within it
what we could do is two things we could
either add
new and more myofibrils in that would be
called
hyperplasia and that would occur if
those satellite cells grouped together
and formed a brand new myofibril that is
probably not what occurs
as the primary mechanism of muscle
growth instead what happens
is that those damaged myofibrils
actually have satellite cells that come
on
and make them bigger so that way those
current myofibrils
actually get bigger and expand the cell
and cause muscle hypertrophy that way
and just to give you an idea of what
this looks like at the cellular level
here's a picture so what you can see
with this picture is the process of
muscle protein synthesis
going all the way from an inactive
satellite cell that was then
activated with the hormonal cascade that
came on after muscle damage
to then move to a group of satellite
cells to then
turn those satellite cells into a
myofiber
so then that myofiber can become part of
a myofibril
which would make a muscle fiber bigger
which would make the entire muscle
bigger
which we would call muscle hypertrophy
so to recap we started with a muscle
fiber
we did training that involved mechanical
tension metabolic stress and muscle
damage
to then cause micro traumas in that
muscle
and then what we did was we signaled
some hormones
and we activated satellite cells to then
start to
generate new muscle proteins and then
that added
myofibrils to our muscle fiber which
then made our muscle fiber bigger
which then made our muscle bigger which
then made your biceps bigger
importantly though this isn't the only
type of hypertrophy what i'm explaining
here is the process of myofibrillar
hypertrophy which is increasing the
myofibrils
and increasing the active contractile
muscle proteins
we could also though have sarcoplasmic
hypertrophy of non-contractile proteins
if you want me to make a video about the
difference between myofibrillar and
sarcoplasmic hypertrophy
or a video about the sliding filament
theory or something like that just go
ahead and leave a comment below
and i will do follow-up videos to this
hopefully this has been helpful for you
if it was
make sure you go ahead and like and
subscribe and if you want to learn more
go ahead and join the strength
conditioning study group on facebook
alright guys thanks for watching and
i'll catch you on the next one
you