Central and peripheral haemodynamics at exercise onset: the role of central command.

Abstract

The involvement of central command in central hemodynamic regulation during exercise is relatively well-known, although its contribution to peripheral hemodynamics at the onset of low-intensity contractions is debated. This study sought to examine central and peripheral hemodynamics during electrically-evoked muscle contractions (without central command) and voluntary muscle activity (with central command). Cyclic quadriceps isometric contractions (1 every second), either electrically-evoked (ES; 200ms trains composed of 20 square waves) or performed voluntarily (VC), were executed by 10 healthy males (26 ± 3years). In both trials, matched for force output, peripheral and central hemodynamics were analysed. At exercise onset, both ES and VC exhibited equal peaks of femoral blood flow (1276 ± 849 vs. 1117 ± 632ml/min, p > 0.05) and vascular conductance (15 ± 11 vs. 13 ± 7ml/min/mmHg, p > 0.05), respectively. Similar peaks of heart rate (86 ± 16bpm vs. 85 ± 16bpm), stroke volume (100 ± 20 vs. 99 ± 27ml), cardiac output (8.2 ± 2.5 vs. 8.5 ± 2.1 L/min), and mean arterial pressure (113 ± 13 vs. 113 ± 3mmHg), were recorded (all, p > 0.05). After ~ 50s, all the variables drifted to lower values. Collectively, the hemodynamics showed equal responses. These results suggest a similar pathway for the initial (first 40s) increase in central and peripheral hemodynamics. The parallel responses may suggest an initial minimal central command involvement during the onset of low-intensity contractions, likely associated with a neural drive activation delay or threshold.