An apparatus includes a support frame, a resilient member, a seat, and a retainer. The resilient member has a first end portion configured to be coupled to the support frame and a second end portion, opposite from the first end portion. The seat is configured to be coupled to the second end portion such that the seat is suspended from the support frame by the resilient member. At least one of the first end portion and the second end portion includes multiple sleeves, each defining an opening therein. A portion of the retainer is configured to be disposed within a first one of the sleeves and coupled to at least one of the seat and the support frame such that a position of the seat relative to the support frame is adjustable by disposing the portion of the retainer within a second one of the sleeves.