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

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 imagesФare cleared reconstructed by ФEIT as four muscle compartments over five weeks experiments, which are called theM₁muscle compartments composed of gastrocnemius muscle,M₂muscle compartments composed of soleus muscle,M₃muscle compartments composed of tibialis-posterior muscle, flexor digitorum longus muscle, and flexor pollicis longus muscle, andM₄muscle compartment composed of the tibialis anterior muscle, extensor digitorum longus muscle, and peroneus longus muscle.Фis inversely correlated with age, namely theФdecreases with increasing age. A paired samplest-test was conducted to elucidate the statistical significance of spatial-mean phase angle in all domain <Ф>_Ωand in each muscle compartment <Ф>_Mwith reference to the conventional phase angle Ф by bioelectrical impedance analysis, muscle grey-scaleG_muscleby ultrasound, and maximal dynamic strengthS_Maxby one-repetition maximum test.Significance. From thet-test results, <Ф>_Ωhave good correlation with Ф andS_Max. In the OG, <Ф^W5>_Ω,Ф^W5, and (S_Max)^W5were significantly higher than in the first week (n= 8,p< 0.05). A significant increase in the phase angle of bothM₁andM₄muscle compartments is observed after five weeks in LG and OG groups. Only the OG group shows a significant increase in the phase angle ofM₂muscle compartment after five weeks. However, no significant changes in the spatial-mean phase angle ofM₃compartment are observed in each group. In conclusion, ФEIT satisfactorily monitors the response of each compartment in calf muscle to long-term EMS training.