What is "John Henryism" as noted in the nonfiction book, Whistling Vivaldi?

Pitt County, North Carolina was the site of a revolutionary study that found that African American men who managed to overcome their circumstances and work their way up did so at the expense of seriously elevating their blood pressure, putting themselves at risk of heart disease, heart attacks and early death. This was especially true of those who believed they could do anything if they just worked hard enough, a trait deemed “John Henryism,” after the African-American folk hero who worked himself to death racing a machine to build railroad tracks in order to make sure that human workers got paid in full.