Influence of one-week hindlimb suspension and intermittent high load exercise on rat muscles

Hindlimb suspension (HS) is a ground-based simulation model for spaceflight commonly used to study the effects of unloading on skeletal muscle. The purpose of the present study was to determine the effects of a daily short-duration, high-load exercise training program in ameliorating the atrophic response and associated adaptations in the mechanical properties of the soleus (SOL) and medial gastrocnemius (MG) muscles to HS. Male Sprague-Dawley rats (mean body weight, approximately 250 g) were assigned randomly to one of three groups: control (CON, n = 7), HS, (n = 7), and HS plus exercise (HS-EX, n = 8). The exercise consisted of rats climbing up a 1-m grid inclined at approximately 85 degrees for eight repetitions with a load equal to 75% body weight attached to their tails repeated four times daily during their active period. Following 7 days, soleus wet weights in the HS and HS-EX rats were 42 and 23% lower than those in the CON rats. The SOL muscle weight to body weight ratio in the HS group was 32% smaller than that in the CON group, whereas it was similar to that of CON in the HS-EX. Maximum tetanic tensions in the HS and HS-EX groups were 44 and 27% less than that in CON, with that in HS-EX being significantly greater than that in HS.(ABSTRACT TRUNCATED AT 250 WORDS)