Adria Biasi, Author at Active Sitting Chair for Posture & Back Pain

Active Sitting as a Solution for Sitting Induced Low Back Pain

Active Sitting as a Solution for Sitting Induced Low Back Pain

Our bodies were not designed for sitting. If you travel back in time, you will find that our ancestors were too busy hunting and gathering to have any time to sit. And, if you think back to your childhood, you will remember that you spent so much more time running, jumping, playing, and much less time sitting.

How did we transform from such an active past to such as inactive present?

Unfortunately, it is today’s modern workforce that is mostly to blame. To make matters worse, our society is faced with the terrible COVID-19 pandemic. People who previously went into the office are now working from home with badly improvised work stations. From sitting on the couch with a laptop to slouching at the kitchen table, we will undoubtedly observe an even greater increase in the amount of sitting and the negative consequences that come with it, including low back pain.

Epidemic proportions of sitting induced low back pain

Low back pain has become an epidemic in our modern society and is now the leading cause of work absence and activity limitations throughout the world.¹ Even if you recover from your first episode of low back pain, chances are, you are going to experience another episode at some point in your life.

Why is this happening? Sitting. As our society continues to sit more and more, the prevalence of low back pain directly increases.

Humans are constantly sitting. We sit to eat, drive, and work. We sit to relax and during other leisure activities. In fact, working age adults in England sit for an average of 9.5 hours per day.

As you go into the office on Monday morning and have a seat at your desk, you may start with relatively good posture. Throughout the day, your posture may worsen, and over the course of a few days, weeks, months, your body adapts to this posture. Areas of the body get tight, other areas become weak, bad habits develop, and pain arises.

Why can’t we simply keep that good posture all day long?

Our bodies intuitively look for ways to decrease energy usage. So, instead of relying on muscles to help maintain a strong posture, we begin to rely on other passive structures such as ligaments, joints, and intervertebral discs. These parts of our bodies were not made for prolonged load-bearing. Therefore, the more we rely on these structures, the more pain we experience, the weaker our back muscles become, and the cycle continues.²

What makes back pain even worse is static sitting. Static sitting refers to maintaining the same posture or position throughout an activity or task. A continuous load is placed through muscles, tendons, joints, discs, and other body parts. This static sitting behavior has been found to be associated with chronic low back pain and pain related disability.³

So much research has been done on sitting induced low back pain. There is no denying the direct relationship that sitting time, whether for work or leisure, has on low back pain intensity.³

While avoiding sitting may be helpful in decreasing pain, some people cannot avoid sitting at least for some portion of their work day. So, if you have to sit, you may as well sit in the best posture with the most optimal muscle activation patterns you can.

How active sitting helps to prevent and reduce sitting induced low back pain 

The opposite of static sitting, discussed earlier, is active sitting. Active sitting refers to engaging muscles, especially of your core, while in a sitting position. One could achieve the effects of active sitting by constantly getting up and moving around, but this is not very efficient for the workplace. Instead, someone could work on actively sitting by using the Symbiotic chair, which is an ergonomically and environmentally friendly chair.

This active sitting chair does not allow you to just passively sit while at work. Preferably, it stimulates your postural and trunk muscles that help keep your body upright and stable. Chairs that allow active sitting are built to still provide support to your sitting bones and low back, while also challenging the user’s muscles by having a flexible seat, mounted on a balancing mechanism. Whether reaching forwards to grab something, turning to answer the phone, and everything in between, this mechanism allows the person to use their own muscles to move around and stay balanced in their chair while still receiving adequate support.

Chairs without this balancing mechanism do not engage the user’s core muscles. Without using these muscles, the body relies on non-contractile tissues for support. And as we learned earlier, this is what can create the vicious cycle of pain.

However, with the use of the balance mechanism, there is an increase in trunk motion, higher muscle activity, constant changes in pressure to the joints, discs, and other structures of the spine, and overall less low back pain.⁴ This postural variation aspect of active sitting is a key component in combating sitting induced low back pain epidemic.

What is postural variation

Postural variation is really the outcome of active sitting.

To better understand this concept, think of riding a horse. If you have ever ridden a horse, you may have noticed that it doesn’t take a significant amount of effort to stay upright and balanced. The horse is walking and moving around, while you stay balanced on top. This balanced poise while sitting for long horseback rides is the same thing that happens with active sitting. Your body is constantly shifting and moving to stay balanced, utilizing postural muscles, but without significant fatigue or realization that you are even doing this.

Now imagine sitting on the couch and watching a movie without any breaks. How do you feel when you stand up once the movie is over? Your back is probably stiff and it may take a few minutes to feel back to normal. This is because your couch or other chair does not have the ability to allow you to have postural variation.

Research has even found that in one hour of sitting, people that develop pain actually move much less than people that do not develop pain. This particular study found that it had nothing to do with the posture, but with the amount of movement. You can think of this as fidgeting for the spine.⁵

While it is unfortunate that so many people have to sit at work, we are lucky enough to have the resources available to create better sitting environments. The path to reducing low back pain, and avoiding it altogether starts with active sitting.

With active sitting, you will be able to have constant postural variation with the ability to use your own muscles to find balance, ending the sitting induced low back pain cycle.

Author: Adria Biasi

US based Doctor of Physical Therapy and Board Certified Orthopedic Specialist

Sources

  1. https://www.jospt.org/doi/full/10.2519/jospt.2012.42.4.A1
  2. https://www.sciencedirect.com/science/article/abs/pii/S1050641112001721
  3. https://www.sciencedirect.com/science/article/pii/S0003687019301279
  4. https://www.sciencedirect.com/science/article/pii/S2095254614000076
  5. https://www.tandfonline.com/doi/full/10.1080/00140139.2019.1661526

 

 

How Important is Core Stability While Sitting At Work?

How Important is Core Stability While Sitting At Work?

You may know some things about core stability, especially as it pertains to exercise and lifting heavy. But you may not realize how important core stability is as it relates to posture and prolonged sitting at work. The strength and stability of your core has the ability to safeguard you from the aches and pains associated with a sedentary desk job.

Evidence based guidelines state that decreased strength is one of the clinical findings associated with acute, subacute, and chronic low back pain. And a review of all of the literature states that there is strong evidence in the use of specific trunk strengthening and endurance exercises, combined with overall physical activity, as an intervention to improve low back pain.¹

There is no denying the fact that most people spend more waking hours working than they do engaging in other fun, relaxing, and leisure activities. So why not include more core stability activities into our long work days?!

First, let’s talk more about our core and what muscles are involved.

What makes up our core stability?

 Core stability is the ability of our low back and abdominal muscles to work together to keep a happy, healthy, neutral posture for prolonged periods of time.

Several muscle groups help to add to core stability. Therefore, to improve core stability, we need to work on not only retraining our postural habits, but also on improving the strength and endurance of our low back and abdominal muscles.

The muscles of your core include:

  • Transverse Abdominis
  • Lumbar Multifidus
  • Erector Spinae
  • Rectus Abdominis
  • Internal / External Obliques

Together, these muscles provide stability to our low back, protecting it against faulty movement patterns and from sitting for hours on end. Think of these muscles working together the way a corset or weight lifting belt works.

One can train and improve core stability throughout different forms of exercise. Some common exercises to improve your stability are through different plank variations, the dead bug exercise, leg raises, and by different forms of sit-ups or abdominal crunches.

While all of these exercises are great, they may not be ones that we can regularly perform throughout the work day. Since we spend so much time at work, it would be best if we find a more feasible way to work on improving core stability in the workplace.

How can we add core stability into the workplace?

If exercising at work is out of the question, one of the simplest ways to increase core stability while sitting at work is through improving our sitting posture.

As we sit, the muscles listed above, our postural muscles, succumb to the effects of gravity. They become less active and we begin to rely on support from our ligaments and joints in our spine to maintain stability. Unfortunately, our ligaments and joints were not made for this prolonged load. It is the job of our postural, core muscles to help absorb this load and handle the stress.

Strengthening these muscles is not enough to correct the problem. We must improve our posture in order to maintain prolonged core stability and proper posture to avoid low back pain and other aches and potential injuries.²

To improve our sitting posture, we should have a chair that allows us to maintain our natural lordotic curve. We don’t want to be slouched forwards, rounding our low back.

Overtime, this prolonged stretch to the low back muscles will cause them to weaken, increasing our reliance on passive structures, your ligaments and joints, to support us.

Besides having the ability to maintain a natural, lordotic curve, we can also improve our core stability, improve our posture, and decrease our risk of developing low back pain by choosing an active sitting chair.

What is an active sitting chair?

An active sitting chair allows you to do exactly what the name implies. Active-Sitting.

Despite sitting for 8 hours a day at work, an active sitting chair will allow you to stay more active during those long work days.

As you sit in an active sitting chair, such as the Symbiotic Chair, you will constantly be using your postural core muscles to move around, stay balanced, and to keep your healthy, natural posture.

Using this chair will not only improve your posture and use of your core muscles, but it will also strengthen and improve the endurance of these muscles.

The Symbiotic Chair was designed with the human body in mind, allowing for frequent movement and changes of your sitting position. In allowing the body to make these constant changes, you will also be strengthening your core stability muscles.

This active sitting chair works through the use of a flexible seat that is mounted on a balancing mechanism. The Symbiotic Chair will not allow you to just sit passively. Instead, it stimulates the musculature responsible for keeping your body upright and stable.

Additionally, the unique sculpted backrest with pronounced lower back support follows a user’s movements in all directions and provides counter-force against the lower back when a user leans against it. This chair was designed as an active working chair to stimulate an upright sitting posture, and this is why it is not equipped with a reclining mechanism like most conventional ergonomic chairs and does not support a lounging position.

The research supports the fact that active sitting does lead to an increase in core muscle activity.³ And an increase in core muscle activity leads to improved strength, endurance, and overall stability.

Something as simple as changing your office chair, from a standard chair to an active sitting chair can make the world of difference in your core stability and posture, and therefore, your chances of developing low back pain.

So, to answer the questions, how important is core stability while sitting at work?

It is undoubtedly, very important. Core stability is easy to improve and can decrease your risk of developing low back pain. By being able to keep your muscles strong and avoid abnormal wear and tear on your ligaments and joints of your spine, you can continue to work and live pain free.

Make the switch today. Improve your core stability by simply actively sitting at work!

 

Author:

Adria Biasi

US based Doctor of Physical Therapy and Board Certified Orthopedic Specialist

Sources:

 

 

 

How To Use Your Laptop Without Damaging Your Spine

How To Use Your Laptop Without Damaging Your Spine

Laptops have revolutionized the way people work. Due to their size, portability, and battery power, laptops can be used anywhere in the world. Despite their convenience, laptops may actually be hurting us much more than we realize.

Have you ever stopped to take a look at how you are sitting when you are using your laptop? Be it on your lap, on your kitchen table, on an airplane, or at your work desk, you most likely will find yourself huddling over the attached keyboard and looking down at your screen.

These nifty devices cause such horrible posture, poor ergonomics, and ultimately a myriad of musculoskeletal problems, most notably in the form of back pain.¹

Laptop design as a cause of back pain

As you have experienced, laptops are very convenient due to the fact that the mouse and keyboard are attached to the computer screen.

What does this mean to us? Sure, we can pack a whole computer into a small bag and take it anywhere we go. But this also means we cannot customize the laptop user experience to work with each individual person’s unique posture, shapes, and sizes.

A laptop is made the same size for a 6-foot person as it is for a 5-foot person.

Not having the ability to separate the screen from the keyboard means you have to sit much closer to the laptop in order to reach the keyboard and mouse.

And, since the keyboard, mouse, and screen are connected, this means you also have to look down at the screen since you are unable to bring the screen to your appropriate eye level.

Compare that to a desktop computer where you can sit comfortably in a chair with the keyboard and mouse pulled in close to you with the screen at the appropriate eye level for you.

Having to look down at the screen and lean in towards the keyboard causes a significant forward head posture, increasing stress and strain to your neck and mid back, as well as constant slouching through your entire spine.

What exactly is forward head posture?

Forward head posture is a way to describe a positioning that many sedentary people adopt through use of laptops or other electronic devices.

Forward head position deteriorated by laptop

In the picture on the left you can see an example of great posture. On the right, this picture is demonstrating forward head posture.

With use of a laptop, one must lower their eyes and shove their head forward to see the screen.

How can this cause back pain?

Well, this posture places a lot of stress on the muscles of the jaw, neck, and upper back.

You can even see how the shoulders round forwards, tightening the chest muscles as well.

The longer you sustain this posture, the more pulling and rounding you will have throughout the entire spine, placing increased stress on the muscles, ligaments, and joints, potentially leading to pain and injury.²

If you think about how heavy your head is, around 5kg or 11 pounds, then it is easy to imagine how much stress is added to your spine the more your head moves forward, away from your center of mass. In fact, for every inch your head moves forwards, it gains another 10 pounds. This means the muscles of your spine have to work that much harder to keep your chin from dropping onto your chest.

That is a lot of added weight and stress to your spine!

What can you do to improve your laptop induced forward head posture?

 While it would be awesome to do away with laptops, it is just not that simple. Even though laptops have caused a lot of pain, they do offer so many benefits.

We just need to be smarter about how to use them. There are several tools available to improve the user experience, decrease forward head posture, and to eliminate back pain.

Here are the 4 issues with laptops and the tools you can use to improve back pain!

1. The height of your screen is going to be too low to maintain good posture.

To fix this you can set your laptop on a desk with a large textbook or sturdy box underneath. You may even purchase a laptop stand, that will look more professional, to elevate your screen.

If you are in a position that allows you to leave your laptop on a desk for prolonged periods of time, you may even buy an external screen. This will increase the height and the size of your screen.

Unfortunately, if you are using the laptop at home on the couch, you may not be able to place the laptop onto a stand. However, even a few pillows under the laptop can help to elevate the screen, decreasing how far you have to slouch down in order to improve your ability to see the screen.

2. The keyboard is not in the best position for you to have good posture. Since the keyboard is attached to the screen, you may not be able to place your elbows at a 90-degree bend with your wrists in a neutral, comfortable position.

To improve the use of your keyboard, you can purchase either a wired or wireless keyboard. This will allow you to have your laptop screen in a better position for your eyes while allowing you to set the keyboard up into an ergonomically friendly position for your shoulders, elbows, and wrists.

3. The mouse is also attached to the keyboard and screen! Same as with the keyboard situation, you will not be able to use the mouse while keeping your elbow at a 90-degree bend with your wrist in a neutral, comfortable position.

You can also purchase a wired or wireless mouse that will allow you to place it in    a more comfortable and ergonomic position for your body.

4. If you are unable to change much about your laptop, you can always improve the chair you are sitting on.

Your chair design can play a large role in your posture, including forward head posture, and back pain. If you are using a laptop, in a less than ideal posture with a horrible chair, then you are definitely set up for failure.

Instead of using a standard chair that has no support or is not the right size for your body, you should invest in a more ergonomically friendly chair. Active sitting chairs are a great option for when you are stuck using a laptop. Since you have to move around a lot more in order to stay comfortable while using a laptop compared to using a desktop, you will want a chair that will move with you, while still supporting you.

The Symbiotic Chair is an active sitting chair that actually has a balance mechanism built into it. This allows you to move your body around, using your own muscles for support, while improving your posture. Plus, the chair still provides adequate support through solid chair and back rest that provides comfortable counter support.

Now as you lean in closer to the screen, overextend your arms to reach the keyboard, or lean back for a break from the screen, you can have a chair that will support you in all positions.

So, if you are stuck using a laptop, try using any of the above external devices and try changing your chair. The benefits are countless, but especially through improving your posture and relieving back pain.

 Sources

 

How Can Your Posture Cause Lower Cross Syndrome?

How Can Your Posture Cause Lower Cross Syndrome?

It is commonly known that poor posture and sitting for prolonged periods of time can wreak havoc on our bodies. From headaches to low back pain and carpal tunnel to sore hips, if you have to sit for work, you will most likely experience some sort of aches and pains, especially if you have poor posture. Lower Cross Syndrome is one of the many conditions that can arise from how you sit and from how much you sit.

Lower Cross Syndrome can really encompass many of the lower body impairments that can arise from the sedentary workplace. Low back pain, hip pain, and even knee pain can present as a symptom of Lower Cross Syndrome.

How can your posture cause Lower Cross Syndrome and what can you do to avoid this? We will dive into these questions. But first, we need to have a review of our anatomy.

What muscles are involved in Lower Crossed Syndrome?

As the name implies, Lower Crossed Syndrome involves muscles of the lower body in a crisscross pattern.

Your Erector Spinae, aka lumbar spine extensor muscles, and your Hip Flexors become stiff and tight. On the other hand, your Gluteus Maximus and your Abdominal muscles become weak and over stretched.

These are all very important muscles that are required to work during nearly every single daily activity. From walking, running, and squatting to sitting, driving, and rolling over in bed, and everything in between. So, if these major muscle groups are not working optimally, you will start to develop even more aches and pains, not just at work while you are sitting, but in everything else you do during the day.

How does Lower Cross Syndrome develop?

Yes, the answer is your posture. Poor posture can lead to Lower Cross Syndrome.

While most of us sit in the workplace, our hips and knees are both bent to 90 degrees of flexion. This position places our Hip Flexors in a shortened position. And, as we sit in this position for hours and hours each day, our will adaptively shorten, causing tightness.

To make matters worse, our Hip Flexor muscles actually attach to the front of our lumbar spine. So, we do not only feel tightness and pain in the front of our hips, but also in our low back. As the muscles pull on the front of the spine, it can create more stress and tension in the joints of the lumbar spine and even cause an increase in our lumbar lordosis, aka the curve of our low back.

As our low back is pulled into this increased lordosis, our low back extensor muscles, the Erector Spinae, are also placed in a shortened position and become tight and overworked. The tightening of these muscles only works to continue to accentuate the tightness of the Hip Flexors, causing a vicious cycle of tightness throughout the hips and low back.

But it does not stop there.

As we continue to sit for hours and hours, our Abdominal muscles and our Glutes actually become weak. This can simply happen due to the fact that we sit for prolonged periods of time and are not using these muscles to facilitate movement or to hold our bodies up into better postural alignment.

But these muscle groups can also become weaker due to the tightness and pulling of our tight Hip Flexors and Erector Spinae muscles.

Because of the attachment of these 2 muscles onto our pelvis, they actually pull our pelvis into an anteriorly rotated position. This tilt places a constant stretch on our Gluteus Maximus and our Abdominal muscles. As these muscles continue to be stretched over time, they become weaker and weaker as they are in a position of disadvantage.

What this means is that the muscle fibers are so stretched out that they cannot contract appropriately.

So many negative changes can happen to our body just by sitting for prolonged periods of time in bad posture. If you develop this unfortunate syndrome, you will most likely notice it first by experiencing low back pain or hip pain.

How to avoid, or recovery from, Lower Crossed Syndrome

Your best bet at avoiding Lower Crossed Syndrome is to improve your posture and to decrease your static sitting time. To aid in avoiding, or recovering from this syndrome, you may also want to work on stretching your low back and hips while strengthening your Glutes and Abdominals.

Unfortunately, sedentary workplaces are becoming the norm. While we may not be able to avoid sitting completely, we can sure do a heck of a lot better on improving our sitting posture.

One of the easiest and more effective ways to improve your sitting posture is through use of an active sitting chair.

Active sitting chairs are unique and offer a much better experience to office employees and desk users when compared to other types of chairs.

Active sitting refers to engaging muscles, especially of your core, while in a sitting position. Having the ability to use your core muscles and your lower leg muscles to help stay balanced and upright in a chair will decrease your risk of being stuck in a static, slumped position.

By being given the opportunity to use your muscles, not only will you avoid the inevitable weakness that occurs with disuse, but you will also be able to avoid the tightening of your hips and low back.

With the constant moving associated with active sitting, your hips will not be stuck in the 90 degrees of hip bend, you won’t be pulling your low back into more of a lordotic curve, and you won’t be tilting your pelvis constantly.

One of the best chairs on the market is the Symbiotic Chair. Not only is it very ergonomically friendly, but it is also an environmentally friendly chair.

Use of the Symbiotic Chair can help you avoid, or recover, from Lower Cross Syndrome. This means improved posture and no more back or hip pain. Therefore, this means a better work experience. And in turn, an overall better quality of life.

Try your Symbiotic Chair today!

Author:

Adria Biasi

US based Doctor of Physical Therapy and Board Certified Orthopedic Specialist

Sources

 

5 Tips on How to Incorporate Microbreaks Into Your Sedentary Work Day

5 Tips on How to Incorporate Microbreaks Into Your Sedentary Work Day

Have you heard of the term “microbreak” before? Perhaps not. This is a relatively new phrase but it is becoming increasingly popular in the workplace, especially for the office or sedentary worker. No matter if you are working from home or in an office space, anyone with a desk job can benefit from microbreaks.

What are microbreaks?

Microbreaks are exactly what they sound like: micro-breaks. These are quick, short breaks taken throughout the workday. Whether you simply stand for 30 seconds or take a 5 minute walk around the office, you are essentially taking a microbreak.

There is no real prescription for taking a quick intermission, as long as you are taking frequent short breaks throughout the day, you will benefit from the positive outcomes associated with microbreaks.

The key is to remember these are short and frequent versus one long break, or a handle full of medium sized breaks. Even if you have the option to take a long lunch with a few 15 minute breaks throughout the day, you should still take regularly scheduled microbreaks.

Why take one?

These brief pauses from work have so many benefits. Not just for your physical, but also your mental health.¹ Think of them as a moment to “reboot”, just like you would do for an overworked computer.

You are provided with the opportunity to get away from your desk, getting out of your prolonged seated position.

You can refresh your mind as you are taking your focus away from work.

All of your muscles and joints can move and stretch out of your sustained desk posture.

Even your eyes have the chance to take a break from straining as they stare at the computer screen.

Research after research is proving that microbreaks really are the next best thing. Anyone from surgeons to typists are benefiting from these. From improved mood and productivity to decreased aches and pains, microbreaks are sure to help, not hurt your work experience.² ³ ⁴

How to take a microbreak?

One of the best ways to go about taking a microbreak is to take a 1-2 minute break every 20-30 minutes. But they can range from 1 to 5 minutes, taken at least once an hour.

The key is to engage in a non-work-related task. Research has found that it is best to stop work, not switch to another work-related activity.⁵

To best implement a microbreak, follow these 5 tips!

  1. Set yourself up for success.

    Make it easy and necessary for you to frequently get up and away from your desk. Try some of these ideas:

    1. Move your printer, copy machine, or fax into a different room, or at least not in reaching distance from your desk.
    2. Stand up while you are talking on the phone.
    3. Enjoy your lunch away from your computer screen.
    4. Use a small cup or bottle of water so that you need to get up several times a day for a refill.
    5. Set a timer on your phone or computer to go off every 20-30 minutes for a reminder to take a microbreak.
  2. Get some fresh air!

    Research shows that 40 seconds of nature is more effective in improving and restoring your attention than a city or concrete scene.⁶

    1. Go look out a window.
    2. Even better, go for a walk around the building.
  3. Use an active sitting chair. Active sitting chairs, like the Symbiotic Chair, allow for micro-movements all day long! While actually getting up and away from your desk is very beneficial, if this is not feasible for your workplace, the Symbiotic chair will help you obtain all of the benefits that microbreaks provide.
    1. Use of a balancing mechanism on these chairs allows you to constantly move around in your chair, using your core muscles for movement and balance, while your “sit-bones” stay supported on a comfortable chair.
    2. Plus, without the use of a sculpted backrest, you can move around with the support you need, while also being provided a counter-force as you lean against it.
  4. Incorporate stretches or light exercise into your microbreaks. Exercise performed frequently, in short bouts, throughout the day has been proven to be effective in:

    1. Improving one’s mood and well-being.
    2. Improving energy and decreasing hunger.
    3. Without negatively impacting productivity.

Try some light stretches, squats, lunges, or brisk walking on your next microbreak!

Don’t engage in work tasks during your microbreak.⁵ Going from typing up a report to responding to emails is not considered a break! If you don’t feel like getting away from your desk, at least try one of these activities:

    1. Watch a funny video.
    2. Scroll through your social media.
    3. Read a news article.
    4. Call a family or friend.
    5. Engage in a conversation with a coworker.

Microbreaks may seem silly and perhaps even a waste of time. But the research cannot be ignored. These short, quick, non-work-related breaks allow you to briefly disengage from your task at hand. Add these up throughout the work day and you will find yourself more productive, with more energy, less pain, and overall happier with your work-life balance.

Even if you simply start incorporating microbreaks through use of an active sitting chair, you are on the right track.

These small intermissions at work have the ability to improve the quality of our entire life. There is no denying the fact that our work spills over into our personal life. So why not do all that you can to improve your work experience, and therefore, your entire life?

Get started today! Try active sitting and set that timer to help keep you accountable!

Author: Adria Biasi

Author is US based Doctor of Physical Therapy and Board Certified Orthopedic Specialist

Sources