Endogenous opioids and runner’s high

Write a 4 page literature review paper written APA style with 4 references. One of them must be from the text book Biological Psychology Klein/Thorne. Pg. 135 and the other 3 must be from a peer reviewed psychological journal. Please see link books.google.com/books?id=p4fNxxuuOgwC&pg=PA135&lpg=PA135&dq=biological+psychology+klein+thorne+endogenous+opioids&source=bl&ots=uJDHEpuUU-&sig=ayfPpPhmlYs6CHftgqytblSzQcg&hl=en&sa=X&ved=0CBsQ6AEwAGoVChMI_IDLoMO9yAIVVu1jCh3tig3J#v=onepage&q=biological%20psychology%20klein%20thorne%20endogenous%20opioids&f=false