A wheelchair can comprise: a frame comprising an upper portion and a lower portion that is coupled to the upper portion so that the upper portion is vertically adjustable with respect to the lower portion. A pair of drive wheels can be coupled to the frame. A plurality (e.g., a pair) of casters are coupled to the frame. Each caster can have a respective swivel axis. At least one caster of the plurality of casters can be configured to be locked to prevent swiveling about its respective swivel axis and unlocked to enable swiveling about its respective swivel axis.