Any cardio exercise will help you. You need to increase your stamina and endurance. So runnng is good, look into some running routines, cycling, rowing machines, they will all help to increase your endurance. As your chosen sport is rugby, obviously running is going to be most beneficial as it the action you do in that sport.
Weights training will also help develope muscles and can also increase endurance.
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This past year I played rugby, but I always found like I was tired 5 minutes into the game. I want to get in shape for next year.
Apart from running, what can I do to help keep my breath?