Shape of the carcass is considered important commercially and is usually assessed using a subjective score for conformation. Carcasses of higher conformation are perceived to have higher lean to bone (L:B) ratios and give joints of better shape at a weight, characterised as shorter and having a greater thickness of muscle. Some of these benefits have been shown, but so has a positive association between conformation and fatness. Purchas et al. (1991) proposed that muscularity indices could be used as an alternative to the conformation score. The objectives of this study were to investigate the relationships between muscularity, shape of joints and composition within breeds and the relationships between different muscularity indices. Knowledge of the latter relationships is important to determine how many indices are required to adequately describe carcass muscularity.