Electrical Characteristics of Calf Muscles Under Neuromuscular Electrical Stimulation*

Objective Electrical impedance tomography (EIT) was applied to study the electrical characteristics of human calf muscles under neuromuscular electrical stimulation (NMES), with the objective of using EIT as a long-term monitoring method to visualize the effectiveness of NMES training on human calf muscles. Methods Sixteen subjects were randomly assigned to a control group (CG, n=8), which kept a normal lifestyle and without NMES or other muscle training; an optimal voltage intensity training group (OG, n=8), in which 23 min of NMES training was performed on the right calf using commercial NMES equipment 3 times a week for 5 weeks. EIT was applied to obtain the conductivity distribution before the start of each training cycle on Monday. Bioelectrical impedance analysis (BIA) was also used to measure the extracellular volume ratio (ECW/TBW) & beta;rl in the right leg. Results In the CG, subjects showed no significant differences in the electrical characteristics of right calf muscle and in the extracellular volume of right calf compared to the first week. However, in the OG, subjects showed the same tendency of increase in the spatial-mean conductivity < & sigma;>M1 of right calf muscle M1 muscle compartment and & beta;rl of right leg compared to the first week. Conclusion NMES training caused an increase in the stimulated muscle compartment spatial-mean conductivity <& sigma;>M1, with the most dramatic increase in <& sigma;w2>M1 of second week, followed by an increase in the third, fourth and fifth weeks compared to the previous week with less growth rate. This implies that a significant increase in muscle fiber volume and sarcoplasmic hypertrophy occurred in the second week, after which the subjects gradually adapted to NMES training and the physiological response of the muscle slowed but continued to grow.