www.elsevier.com/locate/clnu ORIGINAL ARTICLE Deleteriuos effects of immobilization upon rat skeletal muscle: role of creatine supplementation M.S. Aoki a,c, *, W.P. Lima a , E.H. Miyabara a , C.H.A. Gouveia b , A.S. Moriscot a a Laboratory of Molecular Biology of Muscle Plasticity, Department of Histology and Embryology, Institute of Biomedical science, USP, Marcelo Saldanha Aoki, Av. Lineu Prestes, 1524., CEP 05508-900 S * ao Paulo, SP, Brazil b Department of Anatomy, Institute of Biomedical ScienceFUSP, Brazil c Laboratory of Exercise Physiology, Faculty of Physical EducationFUniFMU, Brazil Received 16 July 2003; accepted 10 March 2004 Summary Aim: The aim of the study was to investigate the impact of creatine feeding (5 g kg 1 body weight day 1 ) upon the deleterious adaptations in skeletal muscle induced by immobilization. Methods: Male Wistar rats were submitted to hind limb immobilization together with three dietary manipulations: control, supplemented with creatine for 7 days (along with immobilization) and supplemented with creatine for 14 days (7 days before immobilization and together with immobilization). Muscle weight (wet/dry) was determined in the soleus (SOL) and gastrocnemius (GAS). The analysis of lean mass was performed by DEXA and myosin heavy chain (MHC) distribution by SDS- PAGE. Results: After 14 days of creatine loading, immobilized SOL and GAS total creatine content were increased by 25% and 18%, respectively. Regardless of dietary mani- pulation, the immobilization protocol induced a decrease in the weight of SOL and GAS (Po0.001). However, creatine feeding for 14 days minimized mass loss in the SOL and GAS (Po0.05). Our findings also indicate that creatine supplementation maximizes the expected slow-to-fast MHC shift driven by immobilization (Po0.05). Conclusions: Previous creatine supplementation attenuates muscle wasting induced by immobilization. This effect is associated with the increment of intramuscular creatine content. & 2004 Elsevier Ltd. All rights reserved. Introduction The deleterious effects of hypokinesia upon skele- tal muscle have been intensely investigated for over 40 years. Generally, hypoactivity induces muscle atrophy, slow-to-fast twitch shift and a decrease in force generation capacity. 1–6 These adaptations have been observed in various condi- tions, such as immobilization, 7 hind limb suspen- sion 3 and microgravity, 8 although it is clear that other specific modifications in muscle function occur in these models. Creatine is an organic compound that is directly involved in the muscle energy buffering system. 9 When phosphorylated by creatine kinase, the ARTICLE IN PRESS KEYWORDS Creatine; Immobilization; Skeletal muscle *Corresponding author. Email-address: msaoki@usp.br (M.S. Aoki). 0261-5614/$ - see front matter & 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.clnu.2004.03.004 Clinical Nutrition (2004) 23, 1176–1183