Two electrical pulses applied to the skin can reach deep into the forearm to trigger muscle contractions that were once thought unreachable without needles.

Reaching deep-seated muscles for physical therapy usually requires invasive needles or surgery. Surface electrodes generally only activate the outermost layers of muscle tissue. Interference between two specific electrical frequencies allows the signal to penetrate much deeper into the limb. This technique successfully triggered contractions in the deep muscles of the forearm without causing pain or skin damage. People recovering from strokes or nerve injuries could soon use wearable devices to rebuild strength in muscles that used to be inaccessible.