Tendon injury from excessive use is a common injury in sports activity. It happens when the cumulative load on the tendon is greater than what the tendon can take. There is two parts to this: the first is the cumulative load which means just how much activity is done and just how often this is done. It is important that the tendon has time to get accustomed to those loads or the collective load may go beyond that. That's the second part, just how adapted the tendon is to those loads. Being familiar with these concepts is crucial in being familiar with and treating tendonitis.
One example is, peroneal tendonitis which is an excessive use injury that occurs on the outside of the ankle joint. The collective load in this tendon is higher when physical activity levels are too high or increased too quickly and not sufficient time is given for the tendon to adjust to those high loads. The cumulative load can also be increased by the biomechanics of the foot. For instance, if the supination resistance of the foot is reduced then the peroneal muscles on the outside of the lower limb will have to work harder. That will put an increased strain on the peroneal tendons and then along with training errors that load may possibly go beyond what the tendon can take and it develops tendonitis.
Based on these concepts, peroneal tendonitis is managed by reduction of that cumulative load. That will mean training amounts and frequency really need to be decreased somewhat to permit the tendon to adjust to the loads. The stress in this condition can also be decreased with foot orthoses that evert the foot, which means the peroneal muscles does not need to work as hard. Then the tendon must be given a chance to get used to the loads. This implies that exercising volume and frequency ought to be slowing increased, with lots of rest between training loads to give the tendon to adjust to those loads.