If for medical reason or an injury a runner cannot complete a section and the team decides to continue with the relay, another runner may take over. The substitute may be any other runner from the team and the remaining sections for the injured runner can be split amongst one or several substitute runners. For mixed division teams, substitute runners must be the same gender as the injured runner. Stages may not be shared.Only one runner is allowed per Stage unless an injury occurs on that Stage.

For more information you can follow the link below to the  Rule Book.