An energy storing assistive mechanism includes a barrel having a first pivot end and an open end, a rod having a first end that passes through the open end and is received in the barrel, an elastic structure including two ends that abut against the first end of the rod and the first pivot end, a uni-directional gear rack having a second pivot end away from the barrel, and a locking mechanism fixed to the rod, the locking mechanism comprising a locking member and an actuator assembly that is to drive the locking member to move between a first position where the locking member is engaged with the gear rack, and a second position where the locking member is disengaged from the gear rack.