Athletes in all sports face injury or illness if they train too much. Therefore, it is crucial for them to manage their training load. Monitoring the heart rate is one way to estimate training load. However, there are limitations to a monitor's measurement ability in contact sports like rugby. Another method to estimate training load in contact sports is the rating of perceived exertion of a player, which is based on a questionnaire. It however takes a long time to obtain answers to questionnaires in team sports. As a solution to this problem, we developed a wearable heart rate monitor for rugby players. The garment-type monitor with flank electrodes can measure the heart rate even in rugby training situations. We also propose a method to estimate the training load from the measured heart rate. The method can be used instead of a questionnaire administered to the players and can reduce the labor in the estimation of the training load.