Have you ever watched one of your colleagues stand up from a chair after sitting for a few hours? Depending on how long they’ve been seated for, they often give a big moan, stretch and then do a stiff legged walk while they kind of remain chair shaped.
I’ve always known that it was due to the muscles and joints stiffening up from the lack of movement, but I’ve used to think that you could easily reverse it by doing some stretches later in the day or week. It turns out that you may actually be doing lasting damage to your hip joints through sitting all day – damage that may not be reversed by a couple of sessions of exercise a week. The good news is that you can avoid it!
Understanding the hip joint
The hip joint is a ball and socket joint. The ball (the head of the femur) fits snuggly into a cup (the acetabulum) on the pelvis. The joint surfaces are lined with cartilage. The joint is held together by ligaments and a thick capsule. The capsule is filled with clear joint fluid (synovial fluid) that contains nutrients.
You don’t have any arteries inside your joint or even in the cartilage that lines your joint surfaces. Your joint surfaces have to extract all their nutrients from the joint fluid contained within the joint capsule. To do this, it requires the fluid to move freely inside the joint and it also relies on changes in the pressure inside your joint to force the fluid in and out.
The problem with sitting
Sitting reduces your joint’s nutrition in 3 ways:
The pressure inside the hip joint is at its lowest when the hip is flexed (as it is when sitting) and internally rotated which makes it difficult for the cartilage to extract nutrients from the joint fluid.
Due to lack of movement the joint pressure stays nearly constant and nutrient exchange plummets further.
The sitting position may also cause increased pressure on specific parts of the joint and reduce the joint fluid flow to that part of the joint. Remember that the cartilage are dependent on this fluid for all its nutrient. This can lead to that part of the joint cartilage being starved of nutrients and make it vulnerable to injury.
I have to sit. How can I keep my hips healthy?
Get a sit/stand desk. Please don’t think that all sitting is bad for you. Sitting is a normal activity and it is only when we do it for prolonged periods that it becomes problematic. Alternate hourly between sitting and standing to keep your joints happy.
Go for regular short walks e.g. run up the stairs every hour. Think of this as a snack for your joints! It will create the changes in joint pressure that your cartilage need to exchange nutrients.
Cycle or swim - these activities create lots of joint movement that will help keep your cartilage healthy.
Stretch. Your muscles around your hips become very stiff when you sit for long periods and can restrict your joint range of motion. As explained above, this can lead to nutrient starved cartilage even if you stand up regularly.
Brukner, Peter. Brukner & Khan's clinical sports medicine. North Ryde: McGraw-Hill, 2016.