This paper presents a 4 channel ASIC for sEMG sensing with in-built muscle fatigue and activity feature extraction. Each channel filters and conditions the electrode signal in parallel, while extracting key features for Low Back Pain (LBP) fatigue monitoring and forecasting: Zero Crossing rate and Root Mean Square through sEMG Envelope. The channels are integrated with a Transimpedance Amplifier, an 10-Bit ADC and a Digital Control Unit to digitise and enable transmission of extracted features. Fabricated in TSMC 180nm, these channels present a compact form factor (90$\mu m \times$ 630$\mu m$) and a low power consumption (42.61 $\mu W$), ideal characteristic for wearable devices utilised for long-term monitoring of activities.