There is really one way of maintaining a good health. You have to move. The more you move the healthier you get.
There are 3 races that you can take part in. The longest one is the International Half Marathon with 21.1 km. Apart from competition this course is more like a tour of the city as it will take you to some of the most interesting places in Yerevan.
If 21.1km even sounds tiring for you, you can participate in the 5 km course and still have a lot of fun. For hot-blooded teenagers aged 12-18 there is a shorter course (2.5 km) for some fast triumphs.