**6. Neuromuscular electrical stimulation (NMES)**

Neuromuscular electrical stimulation (NMES) is one of the more recent forms of rehabilitation that works by depolarizing motor neurons to apply an electric current through electrodes implanted on the skin over the targeted muscles, passively stimulating the contraction of the peripheral muscles [26]. It aims to elicit favorable training effects in patients who are unable to take part in PR programs without inducing dyspnea. The stimulation frequency ranges from 8 to 120 Hz, and the stimulation pulse lasts typically between 250 and 400 s. The intensity is steadily increased throughout the entire stimulation, ranging from 10 to 100 mA, depending on the patient's personal tolerance. NMES increased quadriceps strength and exercise capacity, according to a meta-analysis published in 2016. However, there was no statistically significant change in the degree of healthrelated quality of life in patients with moderate-to-severe COPD [14, 27, 28]. NMES has been linked to a reduction in muscle oxidative stress and an increase in type II fiber cross-sectional area with a decrease in type I fiber cross-sectional area in a number of investigations on COPD patients [29]. NMES could be used during times of exacerbation and during admission to the ICU for acute COPD exacerbation because it has a low influence on ventilation, heart rate, and dyspnea [14].
