REGIONAL INTRAMUSCULAR PRESSURE DEVELOPMENT AND FATIGUE IN THE CANINEGASTROCNEMIUS-MUSCLE IN-SITU

Intramuscular pressure (P-IM) was measured simultaneously in zones of the medial head of the gastrocnemius-plantaris muscle group (zone I, p opliteal origin; zone II, central; zone III, near calcaneus tendon) to determine regional muscle mechanics during isometric tetanic contract ions. Peak P-IM averages were 586, 1,676, and 993 mmHg deep in zones I , II, and III and 170, 371, and 351 mmHg superficially in zones I, II, and III, respectively. During fatigue, loss of Pw across zones was gr eatest in zone III (-81%) and least in zone I (-60%) when whole muscle tension loss was -49%. Recovery of P-IM was greatest in zone III and least in zone II, achieving 86% and 67% of initial P-IM, respectively, when tension recovered to 89%. These data demonstrate that 1) regiona l mechanical performance can be measured as PIM within a whole muscle, 2) P-IM is nonuniform within the canine gastrocnemius-plantaris muscl e, being greatest in the deep central zone, and 3) fatigue and recover y of P-IM are dissimilar across regions. These differences suggest dis tinct local effects that integrate to determine whole muscle mechanica l capacity during and after intense exercise.