## 4 Discussion  
Our major findings revealed that compared with the cycle ergometer exercise, the hybrid exercise with cycle ergometer exercises and WB-NMES can be safely performed with continuously increasing VO\({}_{2}\). Additionally, although blood fluidity was transiently exacerbated just after both exercise programs, in vivo sublingual and nailfold microcirculatory parameters remained unchanged, even after the hybrid exercise. The present study showed that hybrid exercise provided more oxygen uptake at the AT level load of the cycle ergometer exercises. During exercise therapy for cardiac rehabilitation, a 40-60% of peak VO\({}_{2}\) or AT level exercise prescription is highly recommended. If hybrid exercises can be performed by cardiac rehabilitation patients, they may be more effective than AT-prescribed exercises. Our results correspond with those of previous studies regarding NMES on the lower extremities [5,11]. Electrical stimulation of the thigh during the cycle ergometer exercise resulted in a significant increase in VO\({}_{2}\) when compared with no electrical stimulation [11]; furthermore, the addition of NMES during certain cycle ergometer exercises significantly increased the VO\({}_{2}\), HR, and respiratory gas exchange ratios [5]. The difference between this and the previous study is that, here, electrical stimulation was applied to the upper limbs and trunk muscles that were not involved in pedaling over a wide range. We expect that more muscles participated in the exercise, explaining the high VO\({}_{2}\) observed during the hybrid exercise. A previous study reported that the combination of voluntary exercise and electrical stimulation induces metabolic activity and energy expenditure, as well as larger muscle fiber recruitment and motor output, when applied under submaximal conditions [19]. At the respiratory compensation point, carbon dioxide emission was higher in the hybrid exercise, even with the same exercise load. In addition to the accumulation of lactate due to vigorous exercise > AT level, lactate was accumulated by sustained contraction of type II fibers by WB-NMES, resulting in a larger carbon dioxide emission as a buffering response. We believe that WB-NMES may have mobilized more muscle fibers as well as the maximal contraction. The lactate levels just after peak exercise were not significantly different between cycle ergometer exercise and the hybrid exercise. The contraction and relaxation times of NMES were not synchronized with voluntary contraction and relaxation of the muscles. NMES causes the antagonist muscles to contract, causing more muscle fibers in the main action muscles to work. Therefore, it has been shown that a high load can be applied to the skeletal muscle by combining electrical stimulation even with low to moderate load exercise [20]. Immediately after performing the exercise, the whole blood passage time--as a parameter of ex vivo blood fluidity--was prolonged; additionally, the blood fluidity temporarily deteriorated during both exercise protocols. There was no synergistic effect caused by the load of WB-NMES on blood fluidity. Vigorous exercise transiently impairs blood fluidity, which has been reported to be a result of increased hematocrit, white blood cell, and platelet counts [8,21]. In fact, hematocrit, white blood cell count, and platelets were also increased by cycle ergometer and hybrid exercises, which is considered to be the reason for the