Intramuscular pressure, force and blood flow in rabbit tibialis anterior muscles during single and repetitive contractions.

The elevated intramuscular pressure (IMP) associated with sustained muscle contraction can affect blood flow, and could influence the long-term viability of functional skeletal muscle grafts. We therefore examined the relationship between force, peak IMP and blood flow in the tibialis anterior muscle of the anaesthetized rabbit. During isometric contractions. IMP was related linearly to force, and only the slope of the relationship varied between animals. During isotonic contractions, however, the highest values of IMP were found at the lowest force levels, and IMP appeared to be related to the amount and speed of shortening. 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 duty cycles of 10-40%, and was unrelated to integrated pressure, integrated force, or depth from the surface. We conclude: (1) that IMP is unlikely to affect mean blood flow during cyclic activity that has a duty cycle less than 40%; and (2) that the clinical use of IMP as a predictor of muscle force appears to be justified only for single isometric contractions, and needs to be interpreted cautiously when contractions involve shortening or fatigue.