Although the exact location of the leg pain is not mentioned, according to the symptoms you report (severe pain in both legs during walking/running) and taking under consideration that you are a proffesional sports athlete, it seems likely that you might be experiencing consequences of various repetitive micro-injuries (such as microfractures, for example-for elite athletes it is very important to know when there is need to take a break, if they are to avoid macroinjuries and the long time periods in which they cannot train or compete). Other reasons could occur when the body is not in good shape and there is too much forcing in exercising to achieve full fitness quickly-and not step-by-step, or due to calcium/magnesium deficiency in the body when muscles could react with spasms. Whatever the true reason might be, severe leg pain is not scientifically proved to be associated with masturbation. You might want to discuss this issue with a doctor-specialist in sports medicine or an orthopaedist, in order to evaluate (through specific imaging and laboratory tests) and solve the problem with the legs pain.