PADI's Freediving Materials are just great. Check it out
http://apps.padi.com/scuba-diving/eMaterialsv3/Uniflips/Web-Portal/70770_1_Freediver_Web.html
Disclaimer:I don't own these materials, just found on the Internet.
http://apps.padi.com/scuba-diving/eMaterialsv3/Uniflips/Web-Portal/70770_1_Freediver_Web.html
Disclaimer:I don't own these materials, just found on the Internet.