Posture Modifies Neuro‐Cardiac Heart Rate Responses at the Onset of Moderate Intensity Isometric Handgrip Exercise

Abstract

BackgroundThe heart rate (HR) response at the onset of moderate intensity isometric handgrip (IHG) exercise is related to neural control of the heart, primarily vagal withdrawal. If so, modest modifications in neuro‐cardiac function by postural shifts should modify the HR response to exercise.ObjectiveThis study examined the effect of supine versus seated postures on the changes in HR and heart rate variability (HRV) at the onset of IHG.Methods13 healthy adults (24±3 years; 6 females) performed IHG at 35% and 50% of maximal voluntary contraction strength (MVC), each lasting 30 seconds and separated by at least one minute of rest. HR (electrocardiogram) and root mean square of successive differences (RMSSD) were recorded from the last 30 seconds of the 1 minute baseline prior to handgrip, and the last 10 seconds of each 30 second handgrip.ResultsBaseline HR increased from 68bpm to 76bpm (p<0.001; d=1) and RMSSD decreased from 56ms to 44ms (p=0.25; d=0.4) when shifting from supine to seated positions. Compared to the supine position, the ΔHR with 35% IHG decreased in the seated position (7bpm to 3bpm; p=0.01; d=0.71). Similarly, the ΔRMSSD with 35% IHG tended to be less in the seated versus supine positions (−31ms to −16ms; p=0.07; d=0.7). During 50% MVC work, the seated position exerted only a modest effect on the IHG‐induced ΔHR compared to supine (18bpm to 13bpm; p=0.06; d=0.47) whereas the ΔRMSSD from baseline to IHG was diminished in seated versus supine positions (−47ms to −22ms; p=0.001; d=0.78).ConclusionWith RMSSD as an indicator of changes in cardiovagal influence, these preliminary results indicate that small changes in posture modify parasympathetic modulation of HR responses at the onset of moderate‐intensity isometric handgrip.Support or Funding InformationSupported by the Natural Sciences and Engineering Research Council of Canada.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.