The objective of this preliminary study is to identify the relative contribution of each tenderness factors for 3 beef muscles of high economical values. Longissimuss dorsi (loin), Tensor fascia latae (tri-tip) and Gastrocnemius (heel) were collected from 10 USDA choice beef carcasses. Each muscle was fabricated into steaks and assigned to a 5 or 21 day aging period. Warner-Bratzler shear force (WBSF), proteolysis (troponin-T degradation), sarcomere length, collagen content, and lipid content were measured (n=60). Heel had the greatest WBSF, followed by tri-tip and loin with the least (4.38, 3.61 and 2.51 Kgf respectively; P < 0.01). Both loin and tri-tip increased in proteolysis from aging with tri-tip having slightly more degradation than loin (P=0.03). Contrarily, heel did not differ in the amount of proteolysis between the aging periods (P > 0.05). Tri-tip had the longest sarcomere, followed by heel and loin (3.01, 2.59 and 1.71 μm respectively; P < 0.01). Heel had the greatest collagen content, followed by tri-tip and loin (6.06, 3.98 and 2.76% respectively; P < 0.01). Finally, tri-tip and loin did not differ in lipid content (8.24 vs. 6.99%; P > 0.05), while heel had significantly lower (P < 0.01) lipid content than the others (2.68%). The results indicated that the 3 retail cuts have different profiles of tenderness contributors. Heel toughness is mostly contributed by the high collagen and low lipid content. Contrarily, loin toughness is mostly contributed by the muscle fiber status with tri-tip in between the two for most measurements.