development [2][3][4][5] and new technology applications. [6][7][8] Together with the emerging Internet of Things (IoT) and Artificial Intelligence (AI) technology, wearable and implantable devices are becoming an irreplaceable component in the modern healthcare system, [9,10] as shown in Figure 1A.Various wearable sensing platforms have been applied in human vital signs monitoring, [11,12] including body temperature, [13] heart rate, [14] respiration rate, [15] blood pressure, [16] and sweat electrolyte. [17] These wearable sensing platforms provide costefficient solutions for long-term fitness monitoring and medical diagnostics purposes. [18][19][20] Moving forward, when certain diseases have occurred, and mere healthcare monitoring is not enough, therapeutic interventions are required. Implantable devices have empowered novel therapeutic interventions. To selectively activate certain excitable cells, integrated optogenetics devices are implanted in the muscle, [21] peripheral nerves, [22] and cortex [23] to deliver light therapy. To mechanically induce tissue contraction in disordered organs, actuators are applied on the heart [24] and bladder. [25] To improve drug diffusion, small-scale drug delivery systems are developed. [26,27] One of the most popular way to deliver therapeutic interventions is to electrically stimulate the nervous system. Well-established treatments include deep-brain stimulation for Parkinson's disease, [28] cochlear implants for hearing loss, [29] visual prosthetics, [30] and brain-machine interfaces for movement restoration. [31][32][33] In addition, emerging energy harvester technologies have enabled direct electrical stimulation on neural tissues for self-powered electrical stimulation to relieve the power supply problem for chronic implantable devices. [34,35] Dating back to 1770, Luigi Galvani first discovered bioelectricity as he made a frog muscle twitch by accidently creating a battery from surgical instruments. [36] Ever since then, people have been exploring to deliver electrical stimulation as therapeutic interventions. However, as an external intervention method, electrical stimulation is essentially different from natural action potentials. In voluntarily controlled movements, motor intentions originated from the cortex travel along individual motor axons to control various skeletal muscles. [37] One Wearable and implantable devices are irreplaceable components in the modern healthcare system. Electrical stimulation on the nervous and neuromuscular system, as a way of therapeutic interventions, has been widely applied to people with neurological disorders and neuromuscular disabilities. The conventional way to study electrical stimulation on the skeletal muscle employs single-channel wire electrodes, which have limited capability to explore the complicated motoneuron distribution in muscle tissue. Here, a microfabricated flexible multiple-channel intramuscular electrode is presented, which enables the study of electrical stimulation using electrode sites of different spatia...