Evaluation of the effectiveness of electrical muscle stimulation on human calf muscles via frequency difference electrical impedance tomography.

Objectives. The human skeletal muscle responds immediately under electrical muscle stimulation (EMS), and there is an immediate physiological response in human skeletal muscle. Non-invasive quantitative analysis is at the heart of our understanding of the physiological significance of human muscle changes under EMS. Response muscle areas of human calf muscles under EMS have been detected by frequency difference electrical impedance tomography (fd-EIT).Approach. The experimental protocol consists of four parts: pre-training (pre), training (tra), post-training (post), and relaxation (relax) parts. The relaxation part has three relaxation conditions, which are massage relaxation (MR), cold pack relaxation (CR), and hot pack relaxation (HR).Main results. From the experimental results, conductivity distribution imagesσp(pmeans protocol = pre,tra,post,or relax) are clearly reconstructed byfd-EIT as response muscle areas, which are called theM1response area (composed of gastrocnemius muscle) and theM2response area (composed of the tibialis anterior muscle, extensor digitorum longus muscle, and peroneus longus muscle). A paired samplest-test was conducted to elucidate the statistical significance of spatial-mean conductivities 〈σp〉M1and 〈σp〉M2inM1andM2with reference to the conventional extracellular water ratioβpby bioelectrical impedance analysis. Significance. From thet-test results, 〈σp〉M1and〈σp〉M2have good correlation withβp. In the post-training part, 〈σpost〉 andβpostwere significantly higher than in the pre-training part (n = 24,p < 0.001). The relax-pre difference ratios of spatial-mean conductivity Δ〈σrelax-pre〉 and the relax-pre difference ratios of extracellular water ratio Δβrelax-prein both MR and CR were lower; on the contrary, the Δ〈σrelax-pre〉 and Δβrelax-prein HR were significantly higher than those in post-pre difference ratios of spatial-mean conductivity Δ〈σpost-pre〉 (n = 8,p < 0.05). The reason for the changes in 〈σp〉M1and 〈σp〉M2are caused by the changes in muscle extracellular volumes. In conclusion,fd-EIT satisfactorily evaluates the effectiveness of human calf muscles under EMS.