For their last fight, Marquez sparked controversy and came under scrutiny for hiring controversial strength guru Angel Hernandez for his last fight against Pacquiao, since Hernandez had been widely known to have a history of being involved in performance-enhancing activities.

A graduate of Texas A&M's exercise science program, Hernandez was known as Angel Heredia, in May of 2008 when he testified in a San Francisco Court that he supplied former track stars Marion Jones and Tim Montgomery with illegal substances.

Hernandez never was convicted of any crimes, although he admitted to giving the blood-booster EPO, growth hormone and insulin to Jones in 2000 at the request of her then-coach Trevor Graham, who was on trial. Heredia also sold banned substances to Montgomery.

Hernandez was hired by Marquez in order to achieve better results than he did in his welterweight debut, a one-sided unanimous decision loss to Mayweather in September of 2009, and has insisted that his state-of-the-art techniques helped Marquez to gain strength and weight for Pacquiao.