What is the fine-grained topic of the following text: Aaron has maintained the bikes of some of Australia's best mountain bike racers, his mechanical skills, wealth of industry knowledge and all round Mr Nice Guy have ensured that as he hits the waves these days to embrace his new passions for surfing and stand up paddling, the locals are happy to share their waves and knowledge with him. Only return the topic.
Aaron's transition from mountain bike maintenance to surfing and stand up paddling in Australia