The use of anabolic-androgenic steroids (AAS) can sometimes increase the incidence of tendon injuries. One fundamental reason is the rapid muscle growth that AAS can induce. Under the influence of AAS, muscles can become significantly larger and stronger in a relatively short period. As the body weight of steroid users increases, the load placed on the tendons also increases. If the tendons do not have enough time (or are unable) to compensate for the increased strain, they may rupture during training or exercise. Therefore, anabolic steroids may indirectly lead to this type of injury in some users, mainly due to the excessive load placed on their connective tissues.

There may also be more direct mechanisms contributing to this type of injury. Similar to skeletal muscle tissue, tendons respond to androgens. Studies have shown that tendons become more rigid under the stimulation of anabolic steroids. With the decrease in tissue flexibility, the relative strength and elasticity of tendons are reduced (essentially lowering the tearing threshold). Additionally, while it is known that anabolic steroids can help the muscle healing process, studies suggest they may actually impair tendon healing.

Despite being a post-injury event, it can be inferred that smaller injury areas might not heal properly, thereby weakening the tissue. These factors, combined with the increased workload due to added weight, explain the higher likelihood of tendon injuries during AAS use.

The data on the potential role of anabolic steroids in connective tissue injuries is ambiguous. Some studies find no association between AAS use and tendon injuries. Overall, these types of injuries are still rare, making it difficult to conclusively link them to AAS use. The amount of AAS used is undoubtedly a significant factor in such injuries. Reports of tendon ruptures often first occur among bodybuilders and steroid users.

On the other hand, muscle injuries (without specific incident events) seem to be very rare in those who use AAS moderately and maintain their body mass at reasonable levels. Many believe that the likelihood of such injuries is due to the slow, steady accumulation of mass with AAS, rather than a sudden, dramatic increase.