Introduction
Injuries to the equine superficial digital flexor tendon (SDFT) play a prominent role in the orthopaedic disorders and form an important threat to both the equine athletic potential and welfare. Therefore this thesis aims at in-depth understanding the development of ECM composition in equine SDFT, and the biological effect of non-invasive physical therapy on tendons.

Tendon development and ageing
In the first part of the thesis two differently loaded regions were chosen deliberately, the mid-metacarpal region (tensile strain) and the sesamoid region (tensional and compressive loading). In the newborn tendon there were significant differences in ECM composition between these 2 loaded regions, which might be probably caused by the fetus movement in utero (chapter II). Directly after birth the functional adaptation of tendon to weight bearing and loading take place for during the first months of life and this can be assumed to affect the loading capacity of tendons and thus may imply potentially serious consequences of early athletic performance. Once maturity had been reached, significant regional differences in the ECM composition that match loading have developed and no dramatic alterations took place with ageing (chapter III). In the mid-metacarpal region there is a higher remodelling rate and in contrast, the sesamoidean region the incidence of injuries is much lower and has a better capability to resist compression. The metabolic activity of the tenocytes maintains only a certain basic level.

Micro-current electrical tissue stimulation (METS)
Results in chapter IV show that tenocytes are sensitive for micro-current therapy. The metabolism of tenocytes increase after the micro-current application but the beneficial range is narrow. If the threshold is passed, the apoptosis level of tenocytes increases, which might severely impair the reparative capacity and delay the repair process. The effects are ambiguous and further research should be done before the clinical use. Furthermore, the transducer placement in dorsal-palmar direction appears to result in less loss of field strength than in medio-lateral or proximo-distal directions (chapter V). The factors that might influence the eventual current level in the target tissue should be taken into account once this type of device is used.

Extracorporeal Shock Wave Therapy
The preliminary study in chapter VI shows that tenocytes increased more than 50% metabolism within 3 hours after one treatment on normal tendons, but there is no significant effect 6 weeks after application. Unexpected, no different effect between different pulses was found. The results might indicate that normal tendon is not very sensitive to shock wave, or the ex vivo measuring system is not sensitive.

Conclusion
Tenocytes apparently perceive the loading or other extraneous stimulation that is transmitted to them through the environment, and translate this into a modification of the extracellular matrix. As collagen turnover is relatively slow at adult age, the process of function adaptation of the ECM at young age maybe of great importance for the development of resistance to injury. Although a full insight into the effects of the tendon therapy is still lacking, there might be a great potential for non-invasive physical therapy, warranting further scientific research.