Tendon injury from too much use is a common injury in sport. It happens when the cumulative strain on the tendon exceeds what the tendon can take. There is two parts to this: the first is the cumulative load and that means simply how much exercise is carried out and just how often this is done. It is vital that the tendon is given time to adapt to those loads or the collective load may exceed that. That's the second aspect, just how adapted the tendon is to those loads. Understanding these concepts is crucial in understanding and managing tendonitis.
By way of example, peroneal tendonitis that is an overuse injury occurring on the outside of the ankle joint. The cumulative load in this tendon is elevated when exercise amounts are too high or increased too quickly and not enough time is provided for the tendon to adjust to those higher loads. The cumulative load can also be increased by the biomechanics of the foot. As an example, if the supination resistance of the foot is low then the peroneal muscles on the outside of the lower limb will have to work harder. That can put an increased force on the peroneal tendons after which combined with training errors that load could go beyond what the tendon can take and it develops tendonitis.
Based upon these concepts, peroneal tendonitis is treated by reducing that collective load. That will mean training volumes and frequency ought to be reduced somewhat to permit the tendon to adjust to the loads. The strain in this condition may also be reduced with foot orthoses that evert the foot, which means the peroneal muscles will not need to work so hard. Next the tendon really should be given an opportunity to adapt to the loads. This means that exercising volume and frequency needs to be slowing increased, with lots of rest between training loads to get the tendon to adjust to those stresses.