http://www.livestrong.com/article/315152-how-to-increase-tendon-strength/ (mirror):
Increase circulation throughout your body to improve the blood flow to your tendons. Part of the problem with tendons is that they aren't vascularized as well as your muscles are, meaning that the blood flow inferior. This can result in poor cell regeneration, weak tendons and possible injury. To improve your circulation, include aerobic exercise alongside your resistance training workout to get the blood flowing. Massaging and applying heat either to particular problem areas like your elbow or heel, can help with blood flow, too.
Has any scientific study demonstrated that aerobic exercises increase the blood around the tendons that attach to the epicondyles at the elbow end of the humerus?
