Complex sentence: He started as a middle distance runner, and competed in 800 meters at 1988 Summer Olympics, then competed in 1500 metres at the 1991 World Championships, the 1992 Summer Olympics and the 1996 Summer Olympics and in 3000 metres at the 1995 IAAF World Indoor Championships.
Split into simpler sentences: He started as a middle distance runner and competed in the 800 meters at 1988 Summer Olympics. He then competed in the 1500 metres at the 1991 World Championships, the 1992 Summer Olympics, and the 1996 Summer Olympics and, in 3000 metres, at the 1995 IAAF World Indoor Championships.