Why do some actions benefit us and others injure us in the long term?

Question

I don't understand this very well. Some repetitive actions - lifting weights, for example - develop our muscles. And other actions can lead to long-term injuries. My old hockey coach told me how lorry drivers are often at risk of injuring their neck from the way they turn it every time they get out of the lorry. How does this work? Why doesn't the lorry driver repeatedly turning his neck strengthen his neck instead?

Answer 1

The nature of those two movements is different. The lorry driver performs continous, non-changing movements which wear out the cartilage of the joints and the tendons and ligaments. Every movement induces slight inflammation in the structures involved. One difference is that the lorry driver performs the same movement every day, without the possibility of rest. While weight lifting utilizes different movements for different exercises, and they are not as repetitive and long lasting, with long recovery breaks between sessions.

The same goes for tennis players for example, who are performing high intensity exercise when playing. They strain the ligaments and muscles of their arms the same way in every stroke, and for long periods of time, and this causes "tennis elbow".

This slightly medical explanation, explains why continuous movement induces injuries. However, the strength-part can be explained in physiological terms.

Basically, for strength to increase you need to strain your muscle intensely (high force), for a short period of time (up to about 30s), while allowing the muscle adequate rest between periods of straining (at least 30s), and long rest between training sessions (about a day). Roughly speaking :) Unless the movement fulfils at least 2-3 of these parameters, then strength will not increase.

So to answer your Q, the lorry driver will not increase strength (maybe a tiny bit though) since he doesnt produce much force in the movement, and he will be more prone to injury due to the repetitive nature of it.

Answer 2

Some of it is person dependent, but it's not the muscles that generally get injured. The things that tend to deteriorate are the joints, cartilage and bursa. These wear down over time, and can lead to injuries.

Every sport/activity when practiced for a long time has its own "signature" injuries due to long time, repetitive motion. Golf, for example, has a long history of lower back injuries in later careers, due to the continued rotation under stress. Swimmers have shoulder problems, tennis/pitchers have elbow problems, etc etc.

There are certainly acute injuries that occur, but the chronic and overuse/long time injuries are just due to the same wear and tear over and over. You can think of it as a hinge that gets opened and closed many many times, eventually the pieces just wear out.