Effects of intermittent ischemia on contractile properties and myosin isoforms of skeletal muscle

Purpose: This study determined the effects of intermittent ischemia on the contractile properties, fatigue (T-f), and myosin heavy chain composition (MHC) in the rat gastrocnemius-plantaris-soleus muscle (GPS) complex. Methods: Fifty rats were divided into four groups: control (C, N = 12), severed (femoral artery) (S, N = 12), exercise (E, N = 13), and severed/exercise (SE, N = 13). Ischemia was elicited only in the SE group by daily exercise and the other groups served as controls. Exercise in the E and SE groups consisted of running on a treadmill similar to 35 min.d(-1), 5 d.wk(-1) for 7 wk. Results: Body weight, muscle weight, and absolute force were less in the SE group compared with those in C (12, 18, and 12% respectively). However, relative force (N.g(-1) of muscle) was greater in the SE group compared with that in C (8%). Maximal shortening velocity (V-max) was lower in the SE group compared with that in all others (10-14%). T-f was less in the S group compared with that in C and E (28 and 30%, respectively). Type IIx MHC increased and type IIb decreased in gastrocnemius and plantaris muscles in SE compared with those in C. Conclusions: These data indicate that intermittent ischemia caused a decrease in muscle mass, maximal force development, and V-max, but had no effect on T-f. The decrease in V-max may have been related to myosin alterations in the muscles.