Effect of aging on the hemodynamic and sympathetic response at the onset of isometric handgrip exercise

Abstract

This study determined whether sympathetic inhibition occurs at the onset of isometric handgrip exercise (HG). We also determined whether age affects the hemodynamic and sympathetic responses to HG. Twelve young and 16 older individuals (age: 24 ± 3 vs.60 ± 9 years) performed four 20‐second HG at 30, 40 and 50% of maximum voluntary contraction (MVC). Beat‐by‐beat heart rate (HR), mean arterial pressure (MAP), cardiac output (Q) and total peripheral resistance (TPR) were assessed by Modelflow, and burst frequency and burst incidence of muscle sympathetic nerve activity (MSNA) were obtained by microneurography. Baseline MSNA burst frequency and incidence were higher in older vs. young individuals (24±9 vs. 12±5 bursts/min, 41±14 vs. 18±8 bursts/100 heartbeat, p<0.001). At 30% MVC, there was no HG effect on HR, MAP, Q, TPR, bursts frequency and incidence in comparison to baseline. At 40% MVC, HG increased HR alone (main effect, p=0.01). At 50% MVC, HG increased HR and burst frequency (main effect, p<0.01). An age effect was observed at 50% MVC, where HG increased HR to a greater extent in young vs. older individuals (15±10 vs. 8±5 bpm, p=0.02). There was no evidence of sympathetic inhibition at the onset of HG in either young or older individuals. Age reduced the HR response but had no impact on the sympathetic response at the onset of HG. This study was funded by CIHR.