Correlation between isometric force and intramuscular pressure in rabbit tibialis anterior muscle with an intact anterior compartment.

To determine the degree to which intramuscular pressure (IMP) and muscle force are correlated in an intact compartment, a custom pressure transducer was inserted into the rabbit tibialis anterior (TA) while activating the muscle via the peroneal nerve and measuring TA muscle force distal to the ankle retinaculum. In general, IMP was more variable compared with muscle force throughout the entire isometric length-tension relationship. In contrast to results obtained on isolated TA muscles, IMP-force relations with the compartment intact were not significantly different between the ascending and descending limbs of the length-tension curve. Specifically, average relative pressure-force coefficients of determination (r2) were 0.76 +/- 0.11 for the active ascending limb and 0.98 +/- 0.01 for the active descending limb. These data demonstrate that muscle force and IMP are fairly well correlated under isometric conditions and that this relationship is not improved by measuring IMP in an intact environment.