A locker includes a pair of spaced-apart upstanding sidewalls and at least one shelf extending between the sidewalls, the shelf and sidewalls defining a compartment. A tray is carried on the shelf in the compartment and supported by a pair of rollers and coupled to a pair of rails mounted on the sidewalls above the shelf, wherein the tray slides forward and backward relative to the shelf and rotates about the rollers. Located on the tray are a set of equipment racks for storing and drying equipment when not in use.

An adjustable seat backrest structure, including a support, an adjusting component, and backrest plates; an adjusting groove extending along an up-down direction is formed at a middle part of the support; a front side of the adjusting component is connected to the backrest plates; an adjusting part is arranged on a rear side of the adjusting component; a left end and a right end of the adjusting part engage with a left side edge and a right side edge of the adjusting groove respectively so that the adjusting part is slidable up and down in the adjusting groove and being capable to be fixed at any position with respect to the adjusting groove, but not capable of moving front and back with respect to the adjusting groove.