Abstract: A fitness machine operable by a user. The fitness machine includes a base that extends in a length direction, a width direction, and a height direction that are perpendicular to each other. A mobile portion is configured to support the user during operation of the fitness machine. A resilient body is configured to provide a resistance against the mobile portion moving towards the base in the height direction. A frame is moveable in the length direction relative to the base to adjust the resistance provided by the resilient body. A fastener assembly moveably couples the frame to the base, where the fastener assembly is configured to expand in the width direction to prevent the frame from moving in the width direction relative to the base during operation of the fitness machine.