INTRAMUSCULAR PRESSURE, FORCE AND BLOOD-FLOW IN RABBIT TIBIALIS ANTERIOR MUSCLES DURING SINGLE AND REPETITIVE CONTRACTIONS

The elevated intramuscular pressure (IMP) associated with sustained mu scle contraction can affect blood flow, and could influence the long-t erm viability of functional skeletal muscle grafts. We therefore exami ned the relationship between force, peak IMP and blood flow in the tib ialis anterior muscle of the anaesthetized rabbit. During isometric co ntractions, IMP was related linearly to force, and only the slope of t he relationship varied between animals. During isotonic contractions, however, the highest values of IMP were found at the lowest force leve ls, and IMP appeared to be related to the amount and speed of shorteni ng. During repeated isometric contractions, the ratio of IMP to force varied with time, stimulation pattern and subject. Mean blood flow did not differ appreciably between repetitive isometric contractions at d uty cycles of 10-40%, and was unrelated to integrated pressure, integr ated force, or depth from the surface. We conclude: (1) that IMP is un likely to affect mean blood flow during cyclic activity that has a dut y cycle less than 40%; and (2) that the clinical use of IMP as a predi ctor of muscle force appears to be justified only for single isometric contractions, and needs to be interpreted cautiously when contraction s involve shortening or fatigue.