Martti Sakari Vainio (born at Vehkalahti) is a Finnish former long distance runner. His achievements in major athletic championships include gold in the 10,000 metres race 1978 European Championships in Athletics in Prague and bronze in the same distance at the 1982 European Championships in Athletics in Athens. At the 1983 World Championships in Athletics he dropped to fourth by a very short margin in the 10,000 metres race, and insenced by that caught the bronze in the 5000 metres, which was also a closely contested fixture, Vainio only assuring his medal by a palpable lunge over the finish line.
At the 1984 Los Angeles Olympics Vainio finished second in the 10,000m, but was caught using steroids and stripped of the silver medal. He had already given a positive sample in Finnish Sports Association internal tests conducted at the Rotterdam Marathon