Chaudhary P, Suryakumar G, Sharma YK, Ilavazhagan G. Differential response of the gastrocnemius and soleus muscles of rats to chronic hypobaric hypoxia. Aviat Space Environ Med 2012; 83:1037–43. Background: The hypothesis of the present study is that the occurrence of oxidative stress with exposure to chronic hypobaric hypoxia will be different in the gastrocnemius and soleus muscles as these two muscles differ in their fiber types. Methods: Male Sprague-Dawley rats were divided into seven groups (I, II, III, IV, V, VI, VII). Groups I-V were exposed to an altitude of 25,000 ft (7620 m) for 0, 3, 7, 14, and 21 d, respectively. Group VI and VII were given curcumin orally and exposed to an altitude of 25,000 ft (7620 m) for 0 and 14 d, respectively. On completion of exposure, the soleus and gastrocnemius muscle were removed and used for various estimations. Results: Maximum changes were observed in 14-d exposed gastrocnemius muscle (GM) as compared to soleus muscle (SM). Lipid peroxidation (nmol · g⁻¹ of muscle) was higher in GM than SM in 14-d exposed rats (43.05 ± 2.96 vs. 27.4 ± 2.35, respectively). Similarly significant increases were observed in free radicals and protein carbonyl on exposure to hypobaric hypoxia. We also observed depletion of the antioxidant, reduced glutathione, in the exposed rats as compared to the control group. A significant reduction of 26% was observed in total protein of the GM as compared to a reduction of 13% in the SM. Myofibrillar proteins were also significantly decreased in the exposed groups. Discussion: Hypobaric hypoxia affects different hind limb muscles differentially and the response of each muscle varies as a function of time. Gastrocnemius muscle is more vulnerable to hypobaric hypoxia-induced oxidative stress in comparison to soleus muscle.