The present study was undertaken to identify the metabolic and contractile characteristics of fast- and slow-twitch skeletal muscles in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). In addition, we investigated the effects of oral creatine supplementation on muscle functional capacity in this model. Transgenic mice expressing a mutant (G93A) or wild type human SOD1 gene (WT) were supplemented with 2% creatine monohydrate from 60 to 120 days of age. Body weight, rotorod performance and grip strength were evaluated. In vitro contractility was evaluated on isolated m. soleus and m. extensor digitorum longus (EDL), and muscle metabolites were determined. Body weight, rotorod performance and grip strength were markedly decreased in G93A compared to WT mice, but were unaffected by creatine supplementation. Muscle ATP content decreased and glycogen content increased in G93A versus WT in both muscle types, but were unaffected by creatine supplementation. Muscle creatine content increased following creatine intake in G93A soleus. Twitch and tetanic contractions showed markedly slower contraction and relaxation times in G93A versus WT in both muscle types, with no positive effect of creatine supplementation. EDL but not soleus of G93A mice showed significant atrophy, which was partly abolished by creatine supplementation. It is concluded that overexpression of a mutant SOD1 transgene has profound effects on metabolic and contractile properties of both fast- and slow-twitch skeletal muscles. Furthermore, creatine intake does not exert a beneficial effect on muscle function in a transgenic mouse model of ALS.