Key Takeaway: Muscle work is either isotonic (concentric or eccentric, where muscle length changes) or isometric (static, where length stays the same but tension changes). It also occurs across four ranges — full, inner, outer, and middle — with most everyday movement happening in the middle range.
In this article, we’ll be studying types of muscle work and ranges of muscle work. We’ve already covered the structure of muscle in one of the previous lessons on muscle structure. So, without further ado, let’s get started.
Types of muscle work
First, let us understand what this muscle work is. An increase in intramuscular tension is called muscle work. There is an increase in tone or tension within the muscles.
So, there are two types of muscle work:
- Isotonic and
- Isometric.
Isotonic is further divided into two types: concentric and eccentric.
So what are isotonic and isometric?
Let me simplify it for you. Just remember two things: tone, meaning muscle contraction, and metric, meaning muscle length.
So here, Iso means ‘same’, okay? So, the first type of muscle is what we call isotonic. This means that the tone of the muscle will remain the same throughout the muscle work. But the length of the muscle will keep changing.
The second muscle type is Isometric. As I just mentioned, iso means ‘same’ and metric means length. Here, the muscle’s length remains the same, while its tone increases or decreases.
Let’s take a look at this example to clarify your concept. Let’s get started.
Isotonic Muscle Work
So first, we start with isotonic muscle work. As I told you, in isotonic, the tone of the muscle and its contraction will remain the same throughout the muscle work. But, for this, the length of the muscle has to change.
So the first point is that the tone of the muscle remains the same, and the second point is that the length of the muscle changes. That is, the length of the muscle can either increase or decrease, depending upon the type of muscle work or movement. This change in length produces movement.
So now there are two types of isotonic muscle work: concentric muscle work and eccentric muscle work. This will make everything clear to you.
Concentric Muscle Work
So first, let’s talk about concentric muscle work. Let me start with an example.
If I am holding a dumbbell and doing flexion and extension of my elbow. So, as I flex, the bulk of my biceps muscle increases. So this is an example of concentric muscle work.
In a concentric muscle, the muscle contracts toward the centre. As you can see in the picture, during elbow flexion, the muscle contraction is directed toward the centre. They’re moving toward each other’s centre, thus contracting the muscle.
The second point is that in concentric muscle work, muscles finally become shorter. When the elbow flexes, the muscle becomes bulkier.
Physiological cost is high — The physiological cost of performing concentric muscle work is high. This is because, ff the energy generated by muscle contraction, only one-fourth is consumed for muscle work or mechanical work. The remaining energy is expended to overcome this initial thirst, plus heat is also produced during exercise. So, some energy is consumed in that heat production.
It’s used to build muscle power. So, the concentric muscle is used to build muscle power.
Another example is the concentric muscle work in the quadriceps. As you can see in the figure, a weight is tied to this leg. So, when we straighten the knee against the weight, the bulk of the quadriceps increases, and the muscle’s length has shortened. And the muscle’s movement was towards the centre, right?
Eccentric Muscle Work
Now let’s move on to eccentric muscle work. Eccentric muscle work is just the opposite, meaning the muscle contracts away from the centre.
To explain this, let’s get back to the same example again. I’m holding a dumbbell and flexing my elbow. We know, during flexion, the biceps muscles are working concentrically. But when I lower it, I have to do it in a controlled manner, slowly to avoid a sudden drop of the dumbbell.
So, in eccentric muscle work, the muscle becomes longer and thinner. Also, the physiological cost is low. Eccentric muscle work requires only one-fourth of the physiological energy required to produce a concentric movement1.
Let me explain this to you with a figure. When we extend our elbow, we do it in a controlled manner; our muscles, the biceps muscles, undergo eccentric contraction.
And in eccentric muscle work, the contraction of the muscle occurs away from the centre, and gradually the length of the muscles increases while the bulk of the muscle reduces.
Clinically, repeated or sustained eccentric contractions are also one of the recognised triggers for myofascial trigger points. If you want to understand this connection in more depth, read our guide on muscle knots: causes, symptoms, and how to relieve them.
Isometric Muscle Work
Isometric muscle work is also called as static muscle work. Because isometric muscle work doesn’t produce any movement. The metric, i.e., muscle length, remains the same, but the muscle tone increases or decreases.
Because the length of the muscle remains the same throughout the muscle work and no movement is produced, it is used in postural muscles to train good posture.
So let me explain this to you with an example. We have hemiplegic patients perform static quadriceps exercises. We make the patient sit in a long sitting position, and then place a pillow or a rolled towel under their knee.
And in this position, we’ll ask the patient to press this pillow with their knees. So, for this, the quadriceps muscles are contracted, but no movement is being produced here.
That’s why we call it isometric exercise or static exercise. And we call this particular exercise a static quadriceps exercise.
Static exercises fatigue the muscles quickly and are used to train the postural muscles. Strong quadriceps muscles are crucial for standing training. That’s why we recommend static quadriceps strengthening exercises for hemiplegic patients or those who are in the post-operative condition after a knee replacement.
Ranges of Muscle Work
Now the second one is the range of muscle work. There are four different types:
- full range,
- inner range,
- outer range, and
- middle range.
Let me simplify it for you with an example.
Look at this semicircle; it starts in a fully contracted position and ends in a fully stretched position.
If I explain this with an elbow movement example, when the elbow is fully flexed, meaning my biceps muscle is fully contracted. And when I fully extend it, my biceps muscle is fully stretched.
Full Range
Let’s try to understand full range. That is, the movement from a fully stretched position to a fully contracted position is what we would call full range muscle work. Because the muscles here are fully stretched, starting and then ending in a fully contracted state. So, this is the full range.
Inner Range
Now, the inner range—from a partially contracted position approximately halfway between fully contracted and fully stretched—means the starting position will be a partially contracted position, meaning somewhere midway.
In this midway, my elbow is flexed, in this position, either I will take it to a fully contracted position, or I will take it to a fully stretched position.
If I’m making a movement in a fully contracted position, that’s inner range, or if I’m making this movement in a fully stretched position, that’s also inner range.
Outer Range
Now, the outer range—what is meant by outer range is that it starts in a fully stretched position, and then there is a partial movement, flexion, extension of the elbow, okay. So we will call it outer range because the starting position is a fully stretched position, and then from this fully stretched position, I am doing partial flexion extension, or partial muscle contraction, or stretching.
So this is the outer range. It’s used to re-educate the muscles—in cases we use this outer range movement or muscle work for muscle re-education.
Middle Range
Now, finally, it’s the middle range. In the middle range, the muscle is neither fully stretched nor fully contracted. The movement occurring in this position is what we call middle-range motion, middle-range muscle work.
It is often used in everyday life. Whatever type of daily work is done, the maximum muscle work occurs in the middle range.
So, I hope this topic is clear to you. If you have any doubts, please leave a comment in the comments section.
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The author is a physiotherapist who has been practising for the last 17 years. He holds a Bachelor's in Physiotherapy (BPT) from SVNIRTAR (Swami Vivekananda National Institute of Rehabilitation and Research), one of the prestigious physiotherapy schools in India.
Whatever he learns dealing with his patient, he shares it with the world through blogs and e-books. He also owns a YouTube channel, "Sunit Physiotherapist" with over 8 lakh active subscribers. Here, he shares everything he gets to learn serving the patient.
