Effects of partial neuromuscular blockade on carotid baroreflex function during exercise in humans

1 This investigation was designed to determine the contribution of central command to the resetting of the carotid baroreflex during static and dynamic exercise in humans. 2. Thirteen subjects performed 3.5 min of static one-legged exercise (20% maximal voluntary contraction) and 7 min dynamic cycling (20% maximal oxygen uptake) under two conditions: control (no intervention) and with partial neuromuscular blockade (to increase central command influence) using Norcuron (curare). Carotid baroreflex function was determined at rest and during steady-state exercise using a rapid neck pressure/neck suction technique. Whole-body Norcuron was repeatedly administered to effectively reduce hand-grip strength by approximately 50% of control. 3. Partial neuromuscular blockade increased heart rate, mean arterial pressure, perceived exertion, lactate concentration and plasma noradrenaline concentration during both static and dynamic exercise when compared to control (P<0.05). No effect was seen at rest. Carotid baroreflex resetting was augmented from control static and dynamic exercise by partial neuromuscular blockade without alterations in gain (P<0.05). In addition, the operating point of the reflex was relocated away from the centring point (i.e. closer to threshold) during exercise by partial neuromuscular blockade (P<0.05). 4. These findings suggest that central command actively resets the carotid baroreflex during dynamic and static exercise.