NOVELTY - The apparatus (10) has an adjustable sliding frame element (24) on a rectangular base frame (28). A four-bar linkage assembly (20) has two pairs of bars with two ends. The second end of each bar of bar pairs is attached to frame element sides. Two foot pedals are mounted on support brackets. Two coil spring and damper assemblies (16) provide resistance during cyclic movement of foot pedals (22) through spring compression. The position of frame element is adjusted by a spring-loaded pin detent mechanism (26). A chair (12) is adjustable in angle and linear distance.    USE - Leg press exercise apparatus e.g. Entirety (RTM: not defined) with lower body negative pressure box in microgravity environments for rehabilitation purposes used by space traveler.    ADVANTAGE - Users of different heights are accommodated, as the position of the sliding frame element is adjustable along the base frame. The chair is adjustable in both angle and linear distance to apply a resistance force to a posterior side of the user's lower extremities during use of the exercise apparatus, to counteract the effects of micro gravity induced syndrome. The microgravity-induced deconditioning is prevented by simulating physiological and biomechanical features of upright exercise and daily activities. The determination whether the kinematics, musculoskeletal loadings, and metabolic rate during supine exercise within the LBNP box are similar to those of upright posture in earth gravity is made. The exercise apparatus is compact and easily transportable. The exercise apparatus is paired with an existing lower body negative pressure box to add an evenly distributed pressure-induced stress to the lower extremities. The technology used in the leg press exercise apparatus is used to enhance rehabilitation protocols. The damper is incorporated to prevent rapid movement in the event that the user's foot slips off the pedal, and helps to discourage high-speed exercise motion. The leg press exercise apparatus incorporates automated adjustments and feedback control to maintain the user's heart rate while providing near optimal resistance curves.    DESCRIPTION OF DRAWING(S) - The drawing shows a side elevation view of the leg press exercise apparatus.    Leg press exercise apparatus (10)    Chair (12)    Coil spring and damper assembly (16)    Four-bar linkage assembly (20)    Foot pedal (22)    Adjustable sliding frame element (24)    Spring-loaded pin detent mechanism (26)    Rectangular base frame (28)