Effect of low-frequency neuromuscular electrical stimulation combined with passive cycle ergometry on hemodynamics in healthy adults

There have been few studies that have examined hemodynamic responses to low-frequency neuromuscular electrical stimulation (LF-NMES), and the effects of combining passive cycle ergometry are still unclear. The purpose of this study was to examine the effects of a combination of LF-NMES and passive cycle ergometry on hemodynamic responses with a primary focus on the Fick principle in healthy adults. A randomized, crossover trial was conducted to evaluate the responses to three types of supine exercises (LF-NMES alone, LF-NMES with passive cycle ergometry, and voluntary cycle ergometry) adjusted to the same exercise intensity as the oxygen consumption of 14 mL/kg/min in 13 healthy adult men. Blood pressure, heart rate, blood lactate concentration, stroke volume (SV), cardiac output (CO), and left ventricular end-diastolic volume (LVEDV) were measured during each exercise in all subjects. The arterial-venous oxygenation difference (A-V̇o₂ difference) was calculated based on Fick's equation. LVEDV, SV, and CO were lower, and the A-V̇o₂ difference and blood lactate concentration were higher in LF-NMES alone than those in voluntary cycle ergometry and LF-NMES with passive cycle ergometry (<i>P</i> < 0.05). The blood lactate concentration was lower in LF-NMES with passive cycle ergometry than that in LF-NMES alone, but slightly higher than that in voluntary cycle ergometry (<i>P</i> < 0.05). Hemodynamic and metabolic responses of exercise with LF-NMES alone seemed consistent with insufficient peripheral perfusion based on the elevation of A-V̇o₂ difference and blood lactate concentration. The findings suggest that combining passive cycle ergometry with LF-NMES improves the insufficient peripheral perfusion induced by LF-NMES alone.<b>NEW & NOTEWORTHY</b> This is the first study to evaluate cardiac output, oxygen consumption, and A-V̇o₂ difference during LF-NMES of endurance exercise modality. LF-NMES alone may not demonstrate hemodynamic responses induced by voluntary endurance exercise, however, demonstrates those when combined with passive cycle ergometry. LF-NMES with passive cycle ergometry may be a more effective approach in cardiac rehabilitation for patients without the ability of voluntary exercise because it may increase cardiac output and venous return as represented by the LVEDV.