Membrane capacitance and characteristic frequency are associated with contractile properties of skeletal muscle

The cell membrane capacitance (Cm) and characteristic frequencies (fc) of tissues can be obtained using segmental bioelectrical impedance spectroscopy (S-BIS). Higher Cm and lower fc are associated with a larger surface area of skeletal muscle fibers with T-tubules in the tissues. Muscle fiber membrane is one of the major physiological factors that influence surface electromyograms (EMGs) as well as the number of recruited motor units so that the amplitude of surface EMG may be correlated with Cm and fc. The aim of the current study was to examine the association of fc or Cm in the lower leg with contractile and neuromuscular properties in the plantar flexors. We analyzed data from 59 participants (29 women) aged 21-83 years. The Cm, fc, and intracellular water (ICW) in the lower leg were obtained using S-BIS. We measured electrical-evoked torque, maximal voluntary contraction (MVC) torque, and amplitude of EMG normalized by the M wave during MVC contraction. The high Cm group had a significantly lower fc and significantly higher MVC torque, estimated maximum torque, twitch torque, and root mean square (RMS) of EMG normalized by the M wave (EMG:M) in the musculus triceps surae compared to the low Cm group (P < 0.05). Cm was positively and fc was negatively correlated with the nRMS of EMG:M in the triceps surae (P < 0.05). S-BIS recordings can be used to detect changes in skeletal muscle membrane capacitance, which may provide insights into the number of T-tubules. The muscle capacitance measured with S-BIS can be predictive of muscle force generation.