Anabolic/androgenic steroid use is sometimes associated with an increased incidence of tendon injury. There are a few potential causes for this. One of the most basic is the rapid growth of the muscles. Under the influence of anabolic/androgenic steroids, the muscles are capable of becoming significantly larger and stronger in a fairly short period of time. As the amount of weight lifted by the steroid user increases, so too does the load placed on the tendons. If the tendons are not given enough time to (or simply cannot) compensate for the added strain, they may rupture during training or athletic performance. Thus, anabolic steroids may indirectly lead to this type of injury in some users, essentially by making them too strong for their own connective tissues.
There may also be more direct mechanisms contributing to this type of injury. Similar to skeletal muscle tissue, the tendons are responsive to androgens. Studies show that under the stimulation of anabolic steroids, the tendons become more rigid. As tissue flexibility is reduced, so is the relative strength and forgiving nature of the tendons (essentially lowering the tearing point). Furthermore, while anabolic steroids are known to aid the healing process in the muscles, studies suggest that they may actually impair the healing of tendon injuries. While this is admittedly a post-injury event, one could speculate that smaller areas of damage might not repair properly, weakening the tissues. These factors, coupled with a rising workload due to expanded strength capacity, could explain a greater potential for tendon injury during anabolic/androgenic steroid use.
The data concerning the potential role of anabolic steroids in connective tissue injury is equivocal. Some studies find no association between AAS use and tendon injury. Overall, these types of injuries are still fairly uncommon. This could make proving an association with anabolic steroid use difficult. The level of AAS use is also undoubtedly a strong contributing factor in this type of injury. When we do see tendon ruptures, they tend to be reported in more advanced bodybuilders and steroid abusers. On the other hand, tendon injury (without a specific accident event) seems to be extremely uncommon in those that use AAS moderately and keep their body mass within reasonable levels. The potential for this type of injury is one reason many believe it is better to accumulate mass slowly and steadily with AAS, instead of rushing to put on the most bulk possible.
Wlliam Llewellyn (2011) - Anabolics