Since I primarily treat people who have been injured on the job, I tend to see a lot of low back injuries, so I apologize if many of my posts are about the spine. With that being said, here is another.
Recently I have been studying the effects of prolonged sitting and repetitive lifting on the low back. Here is what I have found:
1. A recent study looked at creep and fatigue development in the low back when one has been in a flexed position (a bent forward position, like when you are sitting with bad posture or bending over at the back instead of the hips and knees) for a long period of time. Before I proceed I feel I should define creep so people don’t think I’m talking about their neighbor who lives in his parent’s basement, plays computer games in his underwear all day, and breathes through his mouth. Creep can be defined as the gradual elongation of a tissue when it is held in a lengthened position for a long period of time.
Now, back to the study. It was found that when in a flexed position for a prolonged time the passive tissues of the spine (ligaments etc.) undergo creep, and lengthen. After coming out of a flexed position, the passive tissues are too long to help stabilize your spine and the muscles surrounding the spine have to generate more force in order to stabilize. However, muscles undergo creep as well and will fatigue more easily in this lengthened state. So, you are asking muscles that are already fatigued to do more work and you set yourself up for injury.
Another article looked at the affect creep has on sensorimotor control of the muscles around the spine. In other words, all of the muscles in the body have receptors in them that help the muscle adjust to length, tension, and stretch placed on it. One reason (there are many) for these receptors, is to enable the muscles to help protect the joints from taking on excessive force, like a shock absorber. Well, after a muscle has undergone creep, it’s ability to adjust to changes in length and position becomes lethargic and slow. The muscle does not respond as quickly so there is a greater likelihood the joints of the spine may take on too much force (i.e. an injury occurs).
The moral of the story is, don’t stay in one position for too long. Get up and move around every 20-30 min. It may be wise as well to not do any lifting immediately after sitting in a flexed position for a long time.
Now, the question that I had, and still have, after reading this article is, how long does it take before the tissues return to their normal resting state? I have not found that answer yet.
2. The next article I read, studied the effects of repetitive lifting on fatigue of the muscles of the low back. It was of no surprise to me, and probably not to you, that repetitive lifting induced fatigue of the lumbar muscles. What is noteworthy though, is that as the muscles fatigued the peak moment on the spine increased by 36%. In other words, after fatiguing, the muscles are not able to resist the force of gravity on the body when you bend over and the uninhibited force pulls on the spine itself. This will set you up for injury.
The moral of this story is, if you work in a job where you are doing repetitive lifting, make sure you maintain proper lifting mechanics ALWAYS. This also applies to all “weekend warriors” who take on projects that require repetitive lifting.