Cardiovascular responses to human calf muscle stretch during varying levels of muscle metaboreflex activation

The purpose of the present study was to investigate the cardiovascular responses to muscle metaboreflex- and concurrent muscle stretch-induced mechanoreflex activation. Eight subjects (7 males, 1 female) performed 90 s of isometric calf plantarflexion at 0, 30, 50 and 70% of maximum voluntary contraction. During exercise and for 3.5 min postexercise, circulatory occlusion (PECO) was ensured by inflation of a thigh cuff. After 90 s of PECO the calf muscle was stretched for 60 s (Stretch). Heart rate (HR; assessed from ECG), blood pressure (BP; Finapres) and phase of respiratory cycle were recorded. Exercise increased diastolic BP (DBP) from rest by 1 +/- 0.8, 14 +/- 2.5, 29 +/- 3.9 and 35 +/- 3.6 mmHg, during the 0, 30, 50 and 70% conditions, respectively (ANOVA rest versus exercise, P < 0.05). During PECO DBP remained elevated, by 2 +/- 0.4, 8 +/- 0.3, 12 +/- 0.3 and 13 +/- 0.9 mmHg, respectively. Stretch produced a further increase in DBP that was not different between conditions (3 +/- 1.4, 2 +/- 0.8, 3 +/- 1.0 and 3 +/- 0.9 mmHg, for the 0, 30, 50 and 70%, respectively). HR increased during exercise but returned to baseline during PECO. HR increased at Stretch onset in all conditions. No EMG was detected from the gastrocnemius and soleus during Stretch. Our data show that the cardiovascular responses to human calf Stretch are independent of the level of concurrent muscle metaboreflex activation.