Wikipedia
Microtrauma is the general term given to small injuries to the body.
Microtrauma can include the microtearing of muscle fibres, the sheath around the muscle and the connective tissue. It can also include stress to the tendons, and to the bones (see Wolff's law). It is unknown whether or not the ligaments adapt like this. Microtrauma to the skin (compression, impact, abrasion) can also cause increases in a skin's thickness, as seen from the calluses formed from running barefoot or the hand calluses that result from rock climbing. This might be due to increased skin cell replication at sites under stress where cells rapidly slough off or undergo compression or abrasion.
Most microtrauma cause a low level of inflammation that cannot be seen or felt. These injuries can arise in muscle, ligament, vertebrae, and discs, either singly or in combination. Repetitive microtrauma which are not allowed time to heal can result in the development of more serious conditions.