– the structures of the MS System,
– their injuries
– work activities that causes and worsens these injuries
– how to prevent these injuries.
Today we would be taking a closer look at muscles.
Muscular injuries are one of the common work-related injuries. It can affect any part of our body. But there are some areas of the body that are more susceptible to muscle injuries that others. We would discuss that later but first;
What are muscles?
Muscles are fibrous elastic soft tissues found throughout the body. From the eyes, face, ears all the way down to your foot and toes. Muscles are made up of fibres. The more the fibres, the bigger the muscles e.g. your thigh muscles (quads) are bigger than your biceps because it has more fibres. These fibres bound together to contract and relax, producing movement.
Why are Muscles Important?
They are the propellers of all the body’s movement. They are the engine of the musculoskeletal system where movement originates. Like a piston which creates power to the motor to move the vehicle, the muscles generate force to move the body.
Functions of the Muscles
- They generate movement
- Thy maintain posture
- They help to stabilise and strengthen joints during movement.
Types of Muscles
The muscles perform all the movements in the body. Moving food through your digestive system, emptying your bowels and bladder, blinking, smiling, eating, moving arms and legs, writing and of course, your beating heart. But they are not all the same, there are 3 different types of muscles found in the body;
- Smooth muscle
contract involuntarily and are typically found around organs e.g. bladder, digestive tract
2. Cardiac muscle
found in the heart. These muscles never tire and never stops working until …
3. Skeletal muscles
contract voluntary, i.e., we make them move. It is these muscles that make up the musculoskeletal system.
What You Should Know About Movement
- Muscles attach to bones
- Most muscles attach to bones through tendons.
- Movement occurs in joint.
- The change in angle of the joint is known as the range of movement (motion).
- Joints are usually made up of 2 or more bones
- When muscles contract to move the joint, usually one bone moves and the other remains stationary.
How Muscles Work
It all starts from the nerve giving off a signal to the muscle.
The nerve signal excites the muscles, which then contracts, producing tension (force) in the muscle fibres. This is known as Muscle Contraction. When the signal ends, the muscle fibres recoil passively like an elastic band would, and this is known as Muscle Relaxation.
Muscles move only in one direction.
They can only ‘pull’ in one direction. They can’t ‘push’.
Muscles ’pull’ on bones to move the joint. For example, biceps brachii (commonly known as biceps) is the muscle that bends the elbow. It can only bend the elbow it can’t straighten it.
“So, what happens? How do you straighten the elbow?”
Muscles Work in Pairs
To straighten the elbow, another muscle must pull the bone in the opposite direction. In the case of the biceps, the triceps brachii (otherwise known as the triceps) which lies at the back of the bone, straightens the elbow. So, one pulls to bend and the other pulls to straighten.
The quadriceps (thigh muscles). They pull to straighten the knee and the hamstring which lies in the opposite side (back) of the bone, pulls to bend the knee. For movement to occur, they both can’t contract (pull) at the same time. Therefore, when one contracts, the other relaxes. When the biceps contract to bend the elbow, the triceps relaxes. And when the triceps contract to straighten the elbow, the biceps relaxes.
This action is known as the Antagonistic Pair;
The main muscle that contracts to produce movement is the Agonist or Prime Mover.
The muscle that relaxes when the agonist is contracting is the Antagonist. But that’s not all. Musclesnever work in isolation, some other muscles are assisting or stabilizing the joints to allow smooth, pain-free movements. For that to happen, two other roles are acted by other muscles;
This is another muscle close to the prime mover (agonist) that supports the prime mover. It acts like a supporting role in a movie to enhance the action of the agonist. Like in the biceps, the brachialis (a muscle which lies underneath the biceps) work as a synergist to bend the elbow.
4. Fixator/ Stabilizer
As the name implies, it stabilises the joint or joints nearby to allow smooth movement. Again, in the bending of the elbow, the rotator cuff muscles stabilise the shoulder joint from moving.
Newton’s First Law of Motion
I’d have to take you done memory lane. Remember the Newton’s Law of Motion? Specifically, the First Law, that states;
“An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by unbalanced force.”
What Does that Mean?
According to Newton, that means when an object is stationary or moving, the forces acting on the object would;
- equal magnitude (force) and
- act in opposite directions
to balance out each other. It is said to be in equilibrium. Because no unbalanced force is acting on the object, it remains in its state of motion (stationary or moving).
Let’s take an example:
If you were sitting in your office. There are two forces acting on you. First, the force of gravity which acts downwards to keeps you on the chair unlike in space (no gravity – floating). Secondly, the chair exerts an upwards force. Since these two forces are of equal magnitude and in opposite directions, you will remain stationary.
Now, for you to move forward, i.e., you are changing your state from rest to movement, another (unbalanced) force must be introduced to propel you forward. The unbalance force, in this case, would be your muscles.
What Does Newton’s Law of Motion have to do with Muscles?
Remember I said earlier that muscle contraction occurs when tension is generated. This tension is a force that can be exerted on an object e.g. holding a cup. Similarly, the object exerts ‘load’ (force) on the muscle. Therefore in accordance with the Newton’s Law of Motion;
If the force (tension) exerted by the muscles is equal to the force (load) exerted by the object, no movement occurs. In the case of holding a bottle, no joint movement occurs.
But remember that tension (contraction) in the muscle is still present to hold cup and prevent dropping. This type of contraction that results in no change in movement or length of a muscle is known as ISOMETRIC CONTRACTION.
In the same vein, if you wanted to bend your elbow, like in a bicep curl, an unbalanced force must be introduced to move your elbow. The unbalanced force would be coming from an increased muscle contraction. This contraction known as ISOTONIC CONTRACTION would change the muscle length thereby moving the joint.
There are two types of Isotonic Contraction.
- When the movement shortens the muscle
- When the movement lengthens the muscle
In the case of bending the elbow, it would mean the force introduced must be greater than the force already acting on the hand. For that to happen, the muscle (biceps) pulls closer together (shortens) as it contracts. This contraction that shortens the muscles to move (bend) the joint is known as the CONCENTRIC CONTRACTION.
Concentric contractions are the most common type of muscle contraction within the body.
Another example is climbing stairs:
The force generated from the thigh muscles to move (bend) the knees must be greater than the force acting downwards (gravity).
This means that with manual handling e.g. when lifting a box, the bigger the box (load), the greater the force (tension) your muscles must produce to move the box (sometimes up to 6 times)
“Can your muscles cope with that load?”
This brings us to the last type of contraction.
Sometimes movement would occur but the muscle is unable to match the force (load) of the box. That means that the force (load) of the box is greater than the force produced by the muscle. Rather than to pull the joint in the direction of the muscle contraction, like in concentric contraction), the tension from the muscle acts as ‘brakes’ to slow the joint movement, thereby lengthening the muscles. This contraction is known as ECCENTRIC CONTRACTION.
Example: laying down a book, the biceps lengthens while contracting.
Types of Muscle Injuries
1. Muscle Tear
When muscles are stretched beyond their normal limit. They can become overstretched and tear. This injury is known as Muscle Tear. Muscle tear can either be;
a. Acute Muscle Tear:
The injury (tear) is sudden and unexpected. Example; Hamstring Tear which happens when attempting to slow down abruptly from a sprint.
b. Chronic Muscle Tear:
Prolonged repetitive overuse of the muscle. Example; reaching into a deep shelf, jumping down from a height (lorry). Muscle Tears are commonly graded based on the severity;
a. Grade I Muscle Tear known as Sprain
Only a few muscle fibres are torn.
– Localised discomfort or ache
– minimally impairment of muscle strength and function (pix)
b. Grade II Muscle Tear known as Partial or Moderate Tear
A significant number of fibres are torn but the muscle is still intact. Physiotherapy and rest would be needed
– Sharp or stabbing pain
– Impaired muscle strength
– Marked loss of muscle function
– Weight bearing painful
c. Grade III known as Complete Tear or Ruptured
The muscle is completely severed. Surgery would be needed to repair the muscle.
– Sharp pain
– Pain spreads to surrounding areas
– Complete loss of muscle function
– Weight-bearing impossible
Common Areas of Muscle Tear
– Calf e.g. from jumping
– Hamstrings (back of the thigh)
– Quadriceps (front of the thigh)
– Biceps e.g. from manual handling
– Shoulder e.g. from overstretching
– Lower back e.g. manual handling
2. Muscle Tightness
At work, different muscles are used constantly. And over time, the stress on the same group of muscles causes them to tire. Fatigue sets in and muscle contraction weakens. Which then leads to soreness and discomfort. And with prolonged discomfort, it could lead to microtrauma. Microtrauma gradually lead to Muscle Tightness otherwise known as Muscle Knots or Myofascial Trigger Points. However, if adequate rest is given to the muscle when fatigue sets in, they recover and no injury occurs.
Symptoms of Muscle Tightness
- Tight, pulling or cramping sensation
- Throbbing pain
- Limited muscle function
Common Areas of Muscle Tightness
- Lower and upper back e.g. from prolonged sitting
- Neck e.g. from long-distance driving
- Hips e.g. from prolonged sitting
- Shoulder e.g. from manual handling
- Forearm e.g. from gripping tools and pens.
Cold-Related Muscle Injury
Cold weather can increase the risk of muscle tear and tightness. This is because cold lowers the temperature in the muscles causing it to slightly loose its elasticity (tightness). Movements like lifting, sudden movements, precision tasks and using power tools could to muscle injury. Have you ever tried pulling apart bread dough that has been sitting for some hours? It’s too stiff that it breaks off or tears. Warm it up and it becomes pliable again.
According to Polly de Mille, an exercise physiologist at Tisch Sports Performance Centre at Hospital for Special Surgery, cold could also slow down the nerve’s transmission rate (numb feet in winter) and that could throw you off balance causing injury.
How to prevent cold-weather muscle injury
1. Dress appropriately for the weather
For workers working outside, layers of clothing warm up the body reducing stiffness
2. Warm up repeatedly throughout the day
Advice your workers to take breaks indoors e.g. a warn van, warm office. If that is not available, having a heater plugged to the van can be used.
How Would You Know Muscles Has Been Injured?
Muscle injury is difficult to differentiate from a tendon injury unless you are medically trained. However, these prompts would help you take the first aid steps to improve rate of recovery.
- Review the events leading to the injury.
– What was your worker doing? Did it involve overstretching, repetitive movement or manual handling?
- Pain – can they describe the pain? Was it sudden?
- Is there swelling?
How to Assist
1. First Aid
– Apply ice wrapped in a protective cloth to the injured area for about 15 minutes.
– Rest the area
2. Liaise with medical team
If you don’t have any, advice your worker to seek medical attention. The earlier they get seen to, the better and quicker their healing and recovery outcome.
3. Evaluate Job Task
Using ergonomics, assess the jobs tasks and work area.
– Reduce or eliminate repetitive tasks.
– Redesign job
– Provide job aid if necessary
– Provide adequate work space
Work-Related Muscular Injury
Unlike accident or trauma-related (e.g. muscle contusion), work-related muscular injuries occur over time. Muscular injuries usually occur during muscle contraction.
Let’s look in detail how these different muscle contractions would lead to injury. Also find out what you can do to prevent them.
Isometric Contraction (Static)
These contractions are used during when stationary e.g. standing, sitting, lying, bending, hunching, stooping or during manual handling e.g. carrying a pile of folders, lifting boxes, pushing and pulling trolley.
Isometric Contraction and Blood Flow
When muscles are contracting, they consume a large amount of oxygen. This intake of oxygen keeps replenishing the chemicals that cause contraction. For oxygen to be delivered, it is important there is an increase in blood flow to the muscles. However, sustained isometric contraction produces pressure within the muscle that impedes blood flow. The slowdown of blood flow increases the rate of fatigue and increases the risk of muscle tightness (kink).
For job tasks that encourage sustain isometric contraction e.g. carrying load across a distance, prolonged sitting, prolonged computer use, they would increase the risk of muscle injury.
What You Can Do to Prevent Muscle Tightness
1. Move More
Encourage workers to move frequently.
2. Job Design
Design jobs to alternate from sustained to dynamic movements. If possible, eliminate job tasks that promote isometric contraction. For example, instead of carrying shoulder bag or boxes, introduce trolleys, platforms, turntables and pallet lifters.
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3. Size of Load
Reduce the size of load. In accordance to Newton’s 1st Law of Motion: The heavier the load, the greater the strain you place on your hands, legs and back.
4. Train Workers
Educate your workers on manual handling’s best practices. Include health talks, posters, training and toolbox talks. The more often told, the easier to comply.
This is the most common type of muscle contraction. Movement occurs with this contraction. For example;
- – typing, clicking (mouse), walking,
- – swivelling, picking up the telephone,
- – pulling out the drawers,
- – picking and packing items,
- – putting paper in the printer tray
- – stocking and driving.
Hazards of Concentric Contraction
This is one of the major causes of WMSD. Using the same group of muscles for long periods with inadequate or no rest would lead to fatigue.
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Repetitive movements are carried out in your workplace. Like now, I’m typing out this blog-post of over 3000 words. The good thing, is I can take mini-breaks. I pause to think, pause read the post, pause to sip from my mug or just stare out of the window (nice view of the cathedral from where I’m sitting). I have autonomy of my work pace. Of course, I have a target of finishing within three hours, but I can choose to work anyhow.
‘’Does your workers have such autonomy?’’
“Can they take minibreaks?” “Can they have toilet breaks?”
“Can they choose how to do and finish the task?” “Is their work pace sustainable?”
“Can they stretch or exercise if they wanted to?”
“Can they change their tasks and do something different if they choose to?”
What can You Do Is Prevent Repetitive Movement?
1. Job Design
It’s important when you’re designing tasks to;
- evaluate the physical demands of the job.
- spread out the jobs you think may be using the same muscle group. E.g. typing and mousing, picking and packing, loading van and shelving (manual handling).
- carve out mini-breaks in between jobs. Taking frequent smaller breaks are better than one big break.
2. Train Workers
Educate workers on the importance of having breaks and discuss the symptoms of fatigue.
3. Reduce repetitive tasks
Can you automate or semi-automate the tasks? E.g. for a typist, you could introduce Voice Recognition software that can translate spoken words into text. Another example, for picking and packing, could other tasks be introduced to reduce the time spent on picking/packing. You could either enlarge or rotate the task.
This is the most common cause of sudden muscle injury because the muscle lengthens when contraction.
Hazards of Eccentric Contraction
Overstretching to reach items on the workstation. Overstretching when using the computer mouse. Overstretching to pick items from a higher shelf. Stretching backwards on the chair to pick up paper on the floor. Overstretching to push load into a vehicle. These are examples of the various work activities that could lead to overstretching.
2. Manual Handling
Attempting to lift, carry, or put down load that are heavier than your muscles can support would produce eccentric contraction. This sudden and unexpected muscle reaction could cause muscle tear.
What Can You Do to Avoid Injury?
1. Redesign work layout
- Is there adequate space for your workers to move and interact with items around them?
- Are items stored according to how frequently they are used?
- Can your small (short) worker comfortably reach the shelf, workstation or work space?
2. Provide aids and accessories
e.g. steppers, turntables, grabber/reacher, footstools.
3. Educate Workers
On the importance of ‘Keeping items within reach’.
Start with What You Know
I know there is so much information to take in but always start with what you know. A good place to start is by looking into your Incident or Reported Injury Report. If there are tasks that have been reported frequently or that cause muscular injury, conduct an ergonomic assessment. Your goal is to at least, reduce the risks of muscular injuries. Don’t worry if another complaint is reported after your assessment. It takes practice to massively reduce the risk in one assessment. Keep practicing and it would get easier.
Always aim to reduce the risk of WMSD.
Interesting Facts About the Muscle
– It makes up 40% of your total body weight
– You have about 700 muscles in your body and they all have names. Yep! seriously.
– Taking one step, takes about 200 muscles
– The smallest muscles are in your ears.
Author: Ugo Alimi
But in the meantime, join me on my journey to teach you everything you need to know about WMSD.
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