Supraspinatus muscle architectural features increase as a function of animal mass (age), except for sarcomere length, which remains constant over the lifespan. Muscle mass (A) (y = 0.001x + 0.0588, r2 = 0.957, p < 0.0001) increases linearly, normalized muscle fiber bundle length (B) (y = 1.888ln(x) - 0.7084, r2 = 0.797) increases non-linearly, sarcomere length (C) (y = 0.000156x + 2.298 , r2 = 0.20, p = 0.012) increases linearly, and physiological cross-sectional area (PCSA) (D) (y = 0.0007x + 0.1105, r2 = 0.876, p < 0.0001) increases linearly as a function of total body mass.