Muscles 101
Muscles 101
Today’s information is a little dense: however, understanding your horse’s physical makeup is imperative to building a healthy athlete.
There are over 700 muscles in the average horse's body… we aren't going to cover it all but we’re going to highlight the important stuff before we get on with the juicy stuff.
So... without further hesitation, let's dive in!
What muscles make up a horse's mass?
There are three different types of muscles that makeup a horse: skeletal, cardio, and smooth.
Our main focus is going to be on skeletal muscles: however I have defined them all in the graph below.
Skeletal muscles have a giant responsibility in the role of our horses; and we share responsibility to care for these muscles to the best of our ability in order to keep our athletes in optimal shape.
To continue, let’s quickly go over how these muscles function.
In my above graph, I talked about skeletal muscles working in pairs, chains, and groups to achieve motion by one muscle contracting and the opposing muscle relaxing. There’s three different types of muscle contractions:
(brace yourself)
Types of muscular contractions:
concentric, eccentric, and isometric
Concentric muscle activity means that muscles are contracting and shortening.
Eccentric muscle activity means that muscles are contracting and lengthening.
Isometric muscle activity means the muscles are contracting without changing the length of the muscle.
It’s hard to think of a muscle contracting and not imagine concentric activity (the shortening of the muscle) but muscles can contract or activate without changing shape at all (isometric). The key here is to erase the preconceived notion that muscles contracting means that they have to shorten.
Let’s break this down before our brains explode:
(below I've attached a photo illustrated by Marijke de Jong for reference)
We see concentric muscle activity demonstrated by a bicep curl: here you can see the muscles contracting to create enough force to move weight upwards. The second half of the bicep curl shows lengthening in the muscle, creating force to lower weight in a controlled way (eccentric). Finally we see isometric- which is the static hold! Maintaining posture can be incredibly taxing to the muscles- just like this static hold- force is being generated to grip, not move the weight, and the muscles are working overtime to maintain their position.
Let’s apply this to horses!
A collected horse sitting and lifting the weighted hind legs in piaffe is an excellent example of concentric muscle movement- those muscles are contracting, generating a great amount of force to lift the heavier than normal hind leg.
This same horse making a downward transition to a halt after the piaffe- will be elongating the muscles in the hind legs (hello, eccentric) and even in this halt transition the hind legs are generating force.
Finally, imagine you’re trailering your horse. As you make turns, accelerations, and stops in the truck- your horse is activating his muscles not to fall over (hey… I’m not saying you’re a bad driver). These muscles are generating force to hold a position- here an upright one- that's isometric.
Now, as you’re exercising your horse, they will be using all three types of muscle contractions for the duration of the session: but I want you to pay particular attention to isometric muscle activity. A horse lifting its back (and keeping it lifted), engaging its core (and keeping it engaged), finding an uphill neck position, open throat latch, lifted poll… all of that good stuff... those are muscles that are engaging to find a position and stay there (even in movement!)
This is a big and exhausting deal!
Some time ago, I attended a barre class pretty routinely (yeah, yeah, the ballerina class) instructed by a very frightening Russian woman. We would do an absurd amount of plié squats, and as she counted us down from 200-0 we would always have to hold the last rep (isometric activity). My legs would burn and shake, and I’m pretty sure I saw spots a few times. It was extremely tiring, even worse than the squats themselves!
This is similar to when you try a plank position. You hold a position, and even though you aren’t moving, your muscles are engaged and it’s hard as hell.
Never underestimate the amount of work our horses are undergoing to hold their posture.
What are muscles made of?
Basic overview of skeletal muscles:
Skeletal muscles are striated and consist of thousands of muscle units, or bundles. These bundles are composed of muscle fibers: Type I and Type II.
Type I are those slow twitching muscle fibers: these guys are densely made of myoglobin (a red protein that carries and stores oxygen) and mitochondria(remember these? the powerhouse of a cell!)…they are actually so densely made of these that they are red in color! These slow twitching muscle fibers can contract for a long time without tiring out thanks to their makeup, and fuel themselves off of carbohydrates and fats.
Type II are the fast twitching muscle fibers. These fibers contract quickly and with lots of force, but they also tire quickly- because they are sparingly made up of myoglobin and mitochondria. These fibers are responsible for most of our muscle strength, and we have to increase them with strength training exercises.
*Fun fact: the cardiac muscles are structured similarly to skeletal muscles because they can contract and release, and they are also considered striated. However, they are involuntary unlike skeletal muscles (thank the lord) and that’s what makes them their own thing *
(sorry, that is my idea of a fun fact)
SO what’s actually important here?
We are exercising these type I fibers through aerobic exercise, but heavily relying on the type II fibers for strength, quick bursts of energy, jumping powers, etc. We have to work mindfully in our strength training because those fibers tire easily, and they become quite sore as they strengthen.
Speaking of which...
Muscular growth on a cellular level:
After we exercise our horse, their body repairs or replaces damaged muscle fibers. In this process, the muscle fibers will fuse together to form new strands, and these new strands are increased in thickness and strength- which is actually what creates new muscle growth. The cool thing about this process is the body will actually produce satellite cells (similar to stem cells) that are the bonding agent for the muscle fibers to join, and more cells means more mitochondria and myoglobin. As these muscles grow (looking at you type II fibers) they become stronger, more efficient, and don’t tire as quickly!
The process of muscle growth happens when this rate of muscle synthesis (rebuilding) is greater than the rate of muscle breakdown.
Now, muscles don’t magically generate brand new new fibers turning your horse into the hulk; they simply repair or fuse and enlarge the existing muscular fibers. This means, depending on their skeletal makeup (hormone levels and ability to activate satellite cells for muscular repairs...) - some horses are going to bulk up drastically and some will not. Anyhow, these stronger muscles increase their efficiency at recovering and cooling down, increase their ability to flush waste products from soft tissue and blood, and increase their metabolic breakdowns of processing fuel for energy- whew! They’re stronger and more effective!
* It is important to note: We are actively breaking down these muscle fibers while exercising… they aren’t rebuilding during exercise- they rebuild during your horse’s resting state.
We are going to finish up with how muscles attach to the body:
Skeletal muscles are attached to bone, which is how their muscular activity moves the skeletal system. The muscle will taper to connect to a bone (at a place called the “origin”), and this tapered shape means a muscle has two skinny ends and a nice chonky middle- I like to imagine muscles looking like sweet potatoes… which says a lot about me.
Order of operation goes: the “origin” end of the muscle (the one attached to bone), the nice fat middle, and then the other tapered end- which extends into other matter, like tendons or other muscles.
The chunky middle of a muscle is what generally undergoes the stress of cellular re-building, so it can take a little bit of beating, which means the most delicate point of muscle is going to be those tapered ends; especially when they tie into tendons.
Now, tendons have the huge responsibility of controlling joints, and have fewer elastic properties than muscles, which can be cause for injury. These ‘tie in’ areas of muscle and tendon are easily affected by tension and stress and are almost always the first place to for an injury to pop up, and since tendons are gateways to joints- damage to them can cause joint pain.
Maintaining elasticity in the muscle is absolutely crucial for your horse’s health and tendon health! We’re going to go into this even more in depth in Part 2.
THAT'S IT!
So a quick overview:
Three types of muscle that make up a horse: skeletal, cardio, and smooth
Types of muscle movement concentric, eccentric, and isometric
Isometric muscle movement is challenging; don't forget that holding a specific posture/engaging specific muscles is incredibly taxing
Skeletal muscles (and cardio too!) are made up of type I and type II muscle fibers
Strength training takes time because type II fibers tire quickly
Muscular growth happens during the resting state, and the muscle fibers repair themselves or fuse together to create stronger and more effective muscles
Muscles look like sweet potatoes. They are most likely to become injured at the tapered ends- particularly where they connect to tendons.
Prepare yourself for Part 2 of Muscles!
We are going to cover:
Tension in muscles
Healthy musculature vs unhealthy musculature (how you can see and feel it)
What do muscles love and need to grow? *hint, myoglobin*
Thermoregulation: how to read sweat patterns, and how they can fool you!
What's holding you back from lovely topline
Lactic acid: the good, the bad, and why we need it
