Your muscles come in 3 forms, smooth, striated and cardiac. Smooth muscle is involluntary and is found in our internal organs (liver, stomach, lungs etc). Striated or volluntary muscle is, as it’s name suggests under our conscious control, your biceps, triceps and femoral quadruceps are all volluntary muscle,voluntary muscle is also known as skeletal muscle. Cardiac muscles are a combination of volluntary and involluntary muscle and this is what your heart is made out of.
When people talk about muscle micro trauma they are referring to cumulative damage to your volluntary skeletal muscle. When you get a full thickness muscle tear to a large muscle like your femoral bicep (also known as hamstrings and found at the back of your thigh) you know about it. A torn hamstring is very painful and debilitating and it even changes the shape of your leg (until the muscle recovers anyway).
When a full thickness (or almost full) muscle tear happens it stops you dead in your tracks when the strenuousness of what you are attempting is too much for what the muscle is capable of.
Micro trauma as it’s name suggests involves a small amount of muscle trauma that is only mildly uncomfortable and inconvenient if noticable at all. Micro trauma happens when you slightly push yourself too far. Micro trauma as a single isolated incident is no big deal, it is when it keeps recurring before it has the chance to heal that it causes problems.
Your muscles are actually bundles of individual fine strands called myofibrils, myofibrils to a muscle are like the individual strands of plant fibre that are braided together to make rope (except your myofibrils are not plaited). Rope works well until enough of it’s individual fibre strands break and the rest of the rope suddenly gives way.
It is kind of like this when too many of your myofibrils are traumatised, this is typically noticed when you might be strenuously working or exercising in a way that you have done for a long time without any drama when suddenly without warning you get a sudden shock of pain and your strength fails because of cumulative muscle micro trauma.
Few people had heard of muscle micro trauma before Jane Fonda was sued for damages when she showed people a method of muscle stretching on a work out video. Ms Fonda instructed her viewers to do muscle stretches in a jerking way at the end play of the stretches that caused micro trauma.
It is not just stretching exercises that can do this, flexion (weights) exercises full of jerky/rocking movements can cause cumulative muscle trauma. Working strenuously with repetative movements also causes muscle micro trauma.
Even if you are fully convinced that the way you exercise and play are safe and sustainable get some periodic expert advice to make sure you are on the right track and remain mindful of what is age appropriate for you. Even though sport can be a very healthy thing to do some sports create a great deal of emphasis on the repeated uses of some muscles over others. Stretch and get massaged.