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

Purpose 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). Methods Cyclic quadriceps isometric contractions (1 every second), either electrically-evoked (ES; 200 ms trains composed of 20 square waves) or performed voluntarily (VC), were executed by 10 healthy males (26 +/- 3 years). In both trials, matched for force output, peripheral and central hemodynamics were analysed. Results At exercise onset, both ES and VC exhibited equal peaks of femoral blood flow (1276 +/- 849 vs. 1117 +/- 632 ml/min, p > 0.05) and vascular conductance (15 +/- 11 vs. 13 +/- 7 ml/min/mmHg, p > 0.05), respectively. Similar peaks of heart rate (86 +/- 16 bpm vs. 85 +/- 16 bpm), stroke volume (100 +/- 20 vs. 99 +/- 27 ml), cardiac output (8.2 +/- 2.5 vs. 8.5 +/- 2.1 L/min), and mean arterial pressure (113 +/- 13 vs. 113 +/- 3 mmHg), were recorded (all, p > 0.05). After similar to 50 s, all the variables drifted to lower values. Collectively, the hemodynamics showed equal responses. Conclusion These results suggest a similar pathway for the initial (first 40 s) 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.