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

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 imagesσ(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 〈σ〉and 〈σ〉inM₁andM₂with reference to the conventional extracellular water ratioβby bioelectrical impedance analysis. Significance. From thet-test results, 〈σ〉and〈σ〉have good correlation withβ. In the post-training part, 〈σ〉 andβwere significantly higher than in the pre-training part (n = 24,p < 0.001). The relax-pre difference ratios of spatial-mean conductivity Δ〈σ〉 and the relax-pre difference ratios of extracellular water ratio Δβin both MR and CR were lower; on the contrary, the Δ〈σ〉 and Δβin HR were significantly higher than those in post-pre difference ratios of spatial-mean conductivity Δ〈σ〉 (n = 8,p < 0.05). The reason for the changes in 〈σ〉and 〈σ〉are caused by the changes in muscle extracellular volumes. In conclusion,fd-EIT satisfactorily evaluates the effectiveness of human calf muscles under EMS.