Complex sentence: From the middle of 1970s until early 1980s the team was participating to a new amateur championship named "Ethniki Erasitechniki", which was the 3rd highest level of football that time in Greece and it is also the first format of the today's Gamma Ethniki Championship.
Split into simpler sentences: From the middle of 1970s until early 1980s, the team was participating in a new amateur championship named "Ethniki Erasitechniki", which was the 3rd highest level of football at the time in Greece. It is also the first format of the today's Gamma Ethniki Championship.