Oct 2016 01

taxi driving, injury and isometric contraction

By: Dave Wheeler

During this last week, 2 taxi drivers came in on separate occasions, both with the same problem.

It's not quite as coincidental as it sounds: the 1st one came in with a problem in his left shoulder causing pains down his arm... after treating him, he told his colleague (who suffered from the same problem) to come and see me.

2 people presenting from the same trade or profession with the same dysfunction is interesting.

It took a little bit of detective work to figure out what was going on. It turns out that both of them are driving for 8 hours or more every day of the week. They were often resting their left hand on the gear stick.

Or at least, they were both partially resting their left hand on the gearstick. It turns out that neither of them were completely relaxing their arm on the gear. They were holding it in tension ready to change gear when they needed to.

This meant that the muscles in their shoulder, arm and wrist were all contracted ready for action.

It might not sound much, but when the arm was held in that state of "readiness" for 8 hours a day,  there were effects on the muscles. In the 2 cases, the effects were similar, though subtly different because of their age, build, and precise positioning of the arm.

 

Isometric muscle contraction

Isometric muscle contraction is where muscles are kept in a contracted position,  without movement. Think of movies where an interrogation subject is placed in a "stress position" - that's isometric contraction. 

Surprisingly, it's a powerful form of muscle contraction. 

As with more normal muscle contraction (like bicep curls), the effect of any muscle contraction is to build up the muscle. So, keeping the arm out, not-quite-resting on the gearstick for 8 hours a day, actually built up muscle in the shoulder and arm.

A study published in British Journal of Sports Medicine in 2014 by Allen et al showed that in isometric muscle contraction  more damage occurred when the muscle was held lengthened out rather than shortened.

In other words, more muscle damage will occur resting your hand with your arm stretched out on the gearstick than having it bent resting on the steering wheel.

With one of the taxi drivers, it was simply a case of massaging the muscles to relax them. With the other, though, a couple of the muscles at the back of the shoulder had become so big that they were restricting the space available for one of the nerves that runs down the arm, so a bit more work was needed.

 

As ever, if you think I can help, give me a call.