We investigated the effects of chronic creatine (Cr) loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular calcium and on the metabolic profile in rat plantaris, in order to ascertain the bases for our previous observations that Cr loading results in a higher proportion of myosin heavy chain (MHC)-IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: Cr+Sedentary (Cre-Sed); Cr+Run (Cre-Run); control+Sed (Con-Sed); Con+Run (Con-Run). Cre-Run, compared to Con-Run, resulted in 10% and 15% increases in proportion and cross-sectional area of type IIB fibres, and an 11% decrease in IIA fibres (P<0.03). No differences were observed in content of the fast Ca²⁺-ATPase isoform, SERCA1 (P>0.49). Cr feeding alone induced a 41% increase (P<0.03) in slow Ca²⁺-ATPase (SERCA2) content, which was further elevated by 33% with running (P<0.02). Running alone reduced parvalbumin content by 50% (P<0.05). By comparison, Cr feeding alone dramatically decreased parvalbumin content by 75% (P<0.01) but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through Cr loading, alleviates the need for intracellular Ca²⁺ buffering by parvalbumin, and increases the efficiency of Ca²⁺ uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated with run training (P<0.003) but not when combined with Cr feeding. This indicates that Cr loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.