THE EXERCISE PRESSER RESPONSE TO SUSTAINED HANDGRIP DOES NOT AUGMENT BLOOD-FLOW IN THE CONTRACTING FOREARM SKELETAL-MUSCLE

Previous studies have advanced the concept that during sustained handg rip (SHG) reflex increases in blood pressure are able to partially off set increases in tissue pressure and thus effectively maintain increas es in muscle blood flow during mild to moderate levels of sustained ha ndgrip. However, this concept is based upon measurements of blood flow to the entire forearm. The aim of this study was to evaluate this con cept by simultaneously measuring time-dependent changes in systemic ar terial pressure and blood flow in an active muscle during the actual p eriod of exercise. To accomplish this aim, we measured (133)Xenon wash out from the extensor carpi radialis longus muscle over 3 min of SHG a t 15, 30 and 45% of maximal voluntary contraction (MVC). During sustai ned handgrip at 15% MVC, muscle blood flow increased more than 20 fold from rest to exercise (P < 0.05), even though mean arterial pressure increased by only 12+/-4 mmHg. This large exercise-induced hyperaemia was abolished during SHG at both 30 and 45% MVC, despite large and pro gressive increases in mean arterial pressure of 29+/-3 and 54+/-5 mmHg , respectively. We conclude that at levels of handgrip above 15% MVC b lood pressure ceases to be an important determinant of blood flow in t he active skeletal muscle. Importantly, the increases in forearm blood flow that have been reported previously with such levels of static ha ndgrip do not appear to be directed to the most active muscle.