Interaction between muscle metaboreflex and mechanoreflex modulation of arterial baroreflex sensitivity in exercise.

The effect of external calf compression on baroreflex sensitivity (BRS) during electrically evoked plantar flexion and postexercise circulatory occlusion (PECO) was studied. Subjects took part in two experimental trials: control and compression. In both trials, electrically evoked isometric plantarflexion (Stim) was performed at 30% maximum voluntary contraction force for 2 min. During compression, a cuff (inflated to 250 mmHg) was applied to the active calf during exercise and PECO. Sequence analysis carried out on the systolic blood pressure responses, and R-wave-R-wave intervals revealed a rightward shift of the regression line along the pressure axis during Stim in both trials. In the control experiment, BRS was significantly (P < 0.01) increased from 10.37 +/- 1.87 ms/mmHg during Stim to 12.79 +/- 1.62 ms/mmHg during PECO. With external compression, BRS was unaltered between Stim (10.84 +/- 1.86 ms/mmHg) and PECO (11.40 +/- 1.54 ms/mmHg). Because the metabolic conditions were the same in both experiments, the results may best be explained by reactivation of muscle mechanoreceptor activity by external compression during PECO.