Sihine began running at school, inspired by the achievements of compatriot Haile Gebrselassie.
After success at the junior level, he emerged as a leading senior athlete.
In cross country, he won the Cross Internacional de Venta de Baños in 2002 and 2003.
Sihine was one of the three Ethiopians, along with Kenenisa Bekele and Gebrselassie, who swept the gold, silver, and bronze medals in the 10,000 metres at the 2003 World Championships in Paris. Sihine then won the 10,000 metres at the 2003 Afro-Asian Games.
Sihine won a bronze medal at the World Cross Country Championships. He also won a silver medal in the 10,000 metres at the Summer Olympic Gamess in Atlanta, behind Bekele.
Sihine won a silver medal in the 10,000 metres, behind Bekele, and the silver medal in the 5000 metres at the World Championships in Helsinki, Finland.
At the World Cross Country Championships, Sihine finished second behind Bekele.
At the World Championships in Osaka, Sihine took the silver medal in the 10,000 metres, again finishing behind Bekele.
He yet again took a silver medal in the 10,000 metres behind Bekele at the Summer Olympic Games in Beijing, China.
In May, Sihine finished fifth in the 5000 metres at the Samsung DL Golden Gala in Rome, Italy.
Nine days later at the Prefontaine Classic 10,000 metres in Eugene, Oregon, he finished in sixth place, 6.27 seconds behind winner Mohamed Farah.
Sihine attempted his first marathon race at the Amsterdam Marathon, but dropped out after 36 kilometres.
On 7 June, Sihine finished seventh in the 5000 metres at the ExxonMobil Bislett Games in Oslo, Norway. Two weeks later at a 10 kilometre road race in Birmingham, U.K., Sihine finished fourth, just 1.06 seconds behind Bekele, the winner.
In February, he was elected president of the newly formed Ethiopian Athletes’ Association.