Think of the repetitive movements involved in any sport: the arm swing of the golfer, the pedal downstroke of the cyclist, the drop-kick of rugby player, the drop-knee of the climber, or the user of a cardio machine in a gym.
Overuse isn't just restricted to sports though: think of the driver who spends several hours a day in the car and repeatedly moves his foot between accelerator and brake in the same pattern, or the pianist practising for an hour a day the same tricky passage of music.
Ideally, when a movement is done correctly, the whole muscle is used - so the cyclist on the down-stroke should extend his leg and fully plantarflex his ankle (point his toes); but if the seat, handlebars, pedals & cleats aren't set correctly then only part of the muscle will be used. The bike has to cover the same distance, the wheels have to go round the same number of times, but instead of spreading the effort across the whole muscle, only part of it is (over-) used.
It's exactly this that's going on when you see muscle-guys at the gym who can't straighten their arms after bicep curls. The issue isn't that they're necessarily using too much weight, but that they're not fully flexing (and more importantly) fully extending their arm during the exercise. The weight still has to be lifted, but a smaller number of muscle fibres are called into play to lift it.
Microtrauma is the tearing of muscle fibres on a microscopic level.
It happens when individuals bundles of muscle fibres are over-used compared to the surrounding fibres.
When muscle fibres tear, even at the level of microtrauma, they bleed.
The muscle tissue swells up, and within 48 hours scar tissue forms.
This is microtrauma.
Given that it's microscopic, microtrauma is pretty much unnoticeable, even benign.
Since the injury is small, the chances it it won't be noticed, so the person will probably carry on doing the repetitive motion, completely unaware that any damage has taken place.
As the repetitive movement continues, the same bundles of muscle fibres tearing again, bleeding again, swelling again, and healing again with yet more scar tissue being formed.
Once individual fibres have been strained in this way, the surrounding fibres become tense; this secondary tension means that those tense muscles fibres are themselves more susceptible to strain, thereby spreading the micro-trauma within the muscle.
The injury site becomes bigger.
At some point, the injury will become noticeable, usually suddenly, painfully and "out of the blue."
The body is an amazingly adaptive system and if microtrauma occurs and the repetitive pattern that's caused it continues, the nervous system will detect a change in the functioning of muscles and will start to adapt movement patterns.
Muscles nearby will be called in to help out with the movement, putting strain on those newly recruited muscles and their associated tendons. If the pattern continues for a very long time indeed, a pattern of coping with the microtrauma caused by the overuse can develop into an entire compensation patterns..
We've effectively introduced a biomechanical fault into the system. More simply, it's known as the villain and victim principle - the victim that feels the pain might be one muscle, but the problem is actually in the over-use of another, the villain.
Microtrauma develops with repetitive movements - usually when those movements are done using only part of the muscle. So the answer is to make sure that if repetitive movements are necessary, you use the whole muscle:
As ever, if you think I can help, give me a call.