Long-term phase angle muscle imaging under electrical muscle stimulation (EMS) by phase angle electrical impedance tomography

Abstract

Objectives. Phase angle muscle imaging has been proposed by phase angle electrical impedance tomography (ΦEIT) under electrical muscle stimulation (EMS) for long-term monitoring of muscle quality improvement, especially focusing on calf muscles. Approach. In the experiments, twenty-four subjects are randomly assigned either to three groups: control group (CG, n = 8), low voltage intensity of EMS training group (LG, n = 8), and optimal voltage intensity of EMS training group (OG, n = 8). Main results. From the experimental results, phase angle distribution images Ф are cleared reconstructed by ФEIT as four muscle compartments over five weeks experiments, which are called the M 1 muscle compartments composed of gastrocnemius muscle, M 2 muscle compartments composed of soleus muscle, M 3 muscle compartments composed of tibialis-posterior muscle, flexor digitorum longus muscle, and flexor pollicis longus muscle, and M 4 muscle compartment composed of the tibialis anterior muscle, extensor digitorum longus muscle, and peroneus longus muscle. Ф is inversely correlated with age, namely the Ф decreases with increasing age. A paired samples t-test was conducted to elucidate the statistical significance of spatial-mean phase angle in all domain <Ф>Ω and in each muscle compartment <Ф> M with reference to the conventional phase angle Ф by bioelectrical impedance analysis, muscle grey-scale G muscle by ultrasound, and maximal dynamic strength S Max by one-repetition maximum test. Significance. From the t-test results, <Ф>Ω have good correlation with Ф and S Max. In the OG, <Ф W5>Ω, Ф W5, and (S Max)W5 were significantly higher than in the first week (n = 8, p < 0.05). A significant increase in the phase angle of both M 1 and M 4 muscle compartments is observed after five weeks in LG and OG groups. Only the OG group shows a significant increase in the phase angle of M 2 muscle compartment after five weeks. However, no significant changes in the spatial-mean phase angle of M 3 compartment are observed in each group. In conclusion, ФEIT satisfactorily monitors the response of each compartment in calf muscle to long-term EMS training.