The objective of this experiment was to determine the contribution of some biochemical processes of postmortem muscle to the variation in tenderness of beef from Belgian Blue bull cross Holstein-Friesian steers (n=10). These animals were managed optimally from conception to consumption with the aim of reducing tenderness variation. The M. longissimus dorsi (LD) from the left hand side (LHS) and the right hand side (RHS) were analysed for variation in tenderness using Bartletts test. The quality measurements included pH, temperature, Warner Bratzler shear force, sensory tenderness, chemical composition and sarcomere length. Biochemical measurements included myofibrilar proteolysis, glycolytic potential, adenine/inosine ratio and collagen content. No difference for variances or means were observed between LHS and RHS for chemical, quality or biochemical attributes. Biochemical variation was greater than the variation observed in most of the quality attributes measured. Proteolysis was the main biochemical contributor to the variation in shear force tenderness after 2 and 7 as postmortem, but not sensory tenderness. Glycolysis levels and adenine/inosine ratio explained much of the variation in sensory tenderness, but not WBSF. Collagen content in the LD muscles did not explain variation in shear force or sensory tenderness. This would suggest biochemical variation is one of the main contributors to variation in tenderness of beef managed optimally pre- and post-slaughter.