Author and graduation date: Jennifer DAVIS, December, 2000

Committee members: Peter Francis (Chair), Roger Simmons, Karen May-Newman, Richard Lieber

Thesis title: The Relationship Between Intramuscular Pressure and Isometric stress in Isolated Rabbit Tibialis Anterior Muscle

Currently, integrated electromyography (EMG) and kinematics are the standard methods for assessing muscle function in gait analysis. However, the relationship between EMG and muscle tension remains unclear. Moment calculations and anatomical models yield estimates of muscle tension but the solutions are still indeterminate. Previous studies have suggested the use of intramuscular pressure (IMP) as a method for quantifying in vivo muscle function. To quantify the relationship between IMP and muscle tension over an isometric length-tension curve, the tibialis anterior (TA) of New Zealand White rabbits (n = 8, 2.5 + 0.5 kg) was attached to a servomotor, stimulated via a percutaneous electrode on the peroneal nerve, and a 400 gm fiber optic pressure transducer was inserted. Supramaximal force was determined and tetanus was established at 5, 10, 20, 40, 60, 80, and 100 Hz. Optimal Length (Lo) and tension (PO) was established using twitch active tension. The length-tension curve was established using 40 Hz isometric contractions with 2 minutes of rest between contractions. Length measurements began at Lo -50% and progressed to Lo +50% in increments of 5% fiber length. Linear regression quantified the relationship between individual IMP and stress for active and passive contractions on the ascending and descending limb of the length-tension curve. The average length-IMP curve mimicked the average length-stress curve. Individual IMP and stress were highly correlated on the descending limb. Despite less favorable ascending limb correlations, it was concluded that IMP is an appropriate index for assessing both passive and active TA isometric stress for discrete lengths on the length-tension curve.

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