Experiments were performed to determine to what extent increments in esophageal and abdominal pressure would have on arterial blood pressure during fatiguing isometric exercise. Arterial blood pressure was measured during handgrip and leg isometric exercise performed with both a free and occluded circulation to active muscles. Handgrip contractions were exerted at 33 and 70% MVC (maximum voluntary contraction) by 4 volunteers in a sitting position and calf muscle contractions at 50 and 70% MVC with the subjects in a kneeling position. Esophageal pressure measured at the peak of inspirations did not change during either handgrip or leg contractions but peak expiratory pressures increased progressively during both handgrip and leg contractions as fatigue occurred. These increments were independent of the tensions of the isometric contractions exerted. Intra-abdominal pressures measured at the peak of either inspiration or expiration did not change during inspiration with handgrip contractions but increased during expiration. During leg exercise, intraabdominal pressures increased during both inspiration and expiration, reaching peak levels at fatigue. The arterial blood pressure also reached peak levels at fatigue, independent of circulatory occlusion and tension exerted, averaging 18.5-20 kPa (140-150 mm Hg) for both handgrip and leg contrations. While blood pressure returned to resting levels following exercise with a free circulation, it declined by only 2.7-3.8 kPa after leg and handgrip exercise, respectively, during circulatory occlusion. These results indicate that straining maneuvers contribute 3.5 to 7.8 kPa to the change in blood pressure depending on body position.