Background: This study tested the hypothesis that training reduces resting sympathetic activity and improves baroreflex control in both hypertensive and normotensive men but reduces blood pressure only in hypertensive men.

Methods: Middle-aged/older un-medicated stage-1 hypertensive males (mean age 55±3 yrs; n=13) and normotensive controls (mean age 60±5 yrs; n=12) participated in 8 weeks of supervised high-intensity interval spinning training. Before and after training, muscle sympathetic nerve activity (MSNA) and blood pressure were measured at rest and during a sympatho-excitatory cold pressor test (CPT). Based on the measurements, baroreceptor sensitivity and baroreceptor threshold were calculated.

Results: Resting MSNA and baroreceptor sensitivity were similar for the hypertensive and the normotensive groups. Training lowered MSNA (p<0.05), expressed as burst frequency (burst/min), overall, and to a similar extent, in both groups (17 and 27%, respectively in hypertensive and normotensive group), whereas blood pressure was only significantly (p<0.05) lowered (by 4 mmHg in both systolic and diastolic pressure) in the hypertensive group. Training did not (p>0.05) alter the MSNA or blood pressure response to CPT or increase baroreceptor sensitivity but reduced (p<0.05) the baroreceptor threshold with a main effect for both groups. Training adherence and intensity was similar in both groups yet absolute maximal oxygen uptake increased by 15% in the normotensive group only.

Conclusion: The dissociation between the training induced changes in resting MSNA, lack of change in baroreflex sensitivity and the change in blood pressure, suggests that MSNA is not a main cause of the blood pressure reduction with exercise training in un-medicated middle-aged/older men.