Introduction: Previous research has suggested masters athletes require longer than younger athletes to recover following muscle-damaging exercise. Whether older muscle takes longer to repair from muscle damage, or whether older muscle is susceptible to greater levels of muscle damage has been examined in older healthy but untrained individuals. However, limited research has examined muscle damage in well-trained masters athletes. The purpose of the present study was to examine the effect of age on creatine kinase (CK) concentration (a marker of muscle damage) over a 48 h period of regular intense endurance exercise in well-trained athletes.