A highly stretchable and conformable strain sensor fabricated by Ni-doped liquid metal (Ni-GaIn) is designed to record and reconstruct human motion at elbow, knee, heel and even fingers to realize multifunctional human-activity monitoring. The new electronic ink of Ni-GaIn is directly and rapidly printed onto luminous soft substrate to manufacture strain sensor with excellent stretchable and stable electrical properties. Composed of the Ni-GaIn sensors, multifunctional sensor system is demonstrated to work well as human-machine interface, which integrates various functions including measurement and reconstruction. This sensor system provides potential applications for quantifying human motion and is also critical for personal healthcare, prosthetic control and soft robotics in the near future.