So you want to build your own smart wearables for fitness or other purposes? The SparkFun MyoWare Muscle Sensor Kit has you covered. It is an Arduino-powered electromyography (EMG) sensor kit that allows you to measure the electrical activity of a muscle. The LEDs light up as you flex your muscles.
The kit comes with 3-pin stackable headers to make stacking easier. The kit includes a Muscle Sensor, Power Shield, LED Shield, biomedical sensor pads, and other components.