Eight weeks of running, but not stationary cycling, training attenuates the vestibulosympathetic reflex in healthy adults.

Abstract

A possible mechanism for exercise training-induced orthostatic intolerance is attenuation of the vestibulosympathetic reflex (VSR) due to enhanced stimulation of the otolith organs during running. We tested the hypothesis that the VSR is attenuated after 8 wk of running, but not stationary cycling. Arterial blood pressure, heart rate, calf blood flow, and muscle sympathetic nerve activity (MSNA) were recorded in 37 healthy, sedentary subjects (14 males and 23 females, 25 ± 6 years old) during baseline and head-down rotation (HDR) before and after 8 wk of endurance training. Subjects were assigned to running or stationary cycling (n = 13 and n = 12, respectively) or served as controls (n = 12). HDR increased MSNA and decreased calf vascular conductance (CVC) significantly in all groups before training. In contrast, after training, the increase in MSNA was significantly attenuated during HDR in run-trained (before: Δ7 ± 5 vs. after: Δ3 ± 4 bursts/min, P = 0.032) but remained increased in cycle-trained (before: Δ5 ± 5 vs. after: Δ5 ± 3 bursts/min, P = 0.868) and control subjects (before: Δ4 ± 4 vs. after: Δ4 ± 6 bursts/min, P = 0.804). CVC did not decrease from baseline with HDR in run-trained but decreased in cycle-trained and controls after 8 wk (P < 0.02). These data suggest an attenuation of the VSR in run- but not stationary cycle-trained subjects. This is the first study to indicate that endurance running decreases the sensitivity of the otolith organs to changes in gravitational inputs.NEW & NOTEWORTHY Vestibular inputs contribute to blood pressure regulation. Endurance-trained runners have been reported to have lower orthostatic tolerance. We hypothesized that running endurance training would decrease MSNA responses to head-down rotation but not following stationary cycling endurance training. The vestibulosympathetic reflex, as measured by MSNA responses to head-down rotation, was attenuated in run- but not cycle-trained. This study supports the concept that the vestibulosympathetic reflex is diminished by physical activity that chronically enhances otolithic stimulation.