Test panels and shearing machine measurements agree: Tenderness of steak is related to animal's age. Marbling appears unrelated to tenderness, flavor or juiciness. More research on beef tenderness planned.
Goll, Darrel E.; Kline, E. A.; and Miskus, Nancy
"Age - Not Marbling - Indicates Tenderness,"
Iowa Farm Science: Vol. 20
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol20/iss1/2