From Bvio.com

Microtrauma is the general term given to small injuries to the body.

Microtrauma can include the microtearing of muscle fibre, the sheath around the muscle and the connecting tissue. It can also include stress to the tendons.

Most microtrauma cause a low level of inflammation that can not actually be seen and are not necessarily felt. These injuries can arise in muscle, ligament, vertebrae, and discs, either singly or in combination.

One example of microtrauma is in the form of microtears to the muscle fibres as a result of stresses the body is not accustomed to - such as an intensive workout.

Repetitive microtrauma, which are not allowed time to heal can result in the development of more serious conditions.

Back pain can develop gradually as a result of microtrauma brought about by repetitive activity over time. Because of the slow and progressive onset of this internal injury, the condition is often ignored until the symptoms become acute, often resulting in disabling injury. Acute back injuries can arise from improper lifting techniques. While the acute injury may seem to be caused by a single well-defined incident, the real cause is often a combined interaction of the observed stressor coupled with years of weakening of the musculoskeletal support mechanism by repetitive microtrauma. It should be noted however that physiotherapists encourage exercise as it is deemed an important factor in reducing back pain.