The HLS model involves suspending rats by the tail base to produce a 30° head-down position that complements the human 6° head-down tilt utilized in bed-rest studies.
A ground-based model for studying hypergravity is centrifugation. With the use of proper controls for Coriolis effects, centrifugation allows for an infinite number of graded increases in gravitational load and is therefore applicable to a broad range of gravity-related questions. Acute centrifugation is used to mimic the hypergravity associated with launch and landing, whereas chronic centrifugation is used to study the long-term effects of increased gravity on biological systems.
Ground-based models have been used successfully in studies of the musculoskeletal system, to validate spaceflight experiments, and to define adaptation to the space environment. Advantages of using ground-based models are the ability to control environmental factors more effectively than can often be achieved in spaceflight studies. Animals adapt well to ground-based models, thereby minimizing stress-associated physiological effects. Therefore, ground-based models are potentially valuable tools for investigating reproduction during exposure to hyper- and hypogravity.