Bilateral symmetry of ground reaction force with a motor-controlled resistance exercise system using a mechanical advantage barbell for spaceflight.

The reduced gravity experienced during spaceflight leads to muscle and bone atrophy, and resistance exercise has proven to be an effective countermeasure. Thus, a compact computer-controlled electric-motor resistance exercise system is being developed for NASA. In order to save power, space, and weight, the torque specifications of the motor were reduced by half because of a unique barbell design that employs a two-to-one mechanical advantage. Since the force-generating motor is on one side of the barbell, there is the potential for asymmetric barbell loading. Therefore, the purpose of this preliminary study is to compare the unilateral ground reaction forces (GRF) of the new barbell of the motor and ground sides. Multiple repetitions of fixed tempo deadlift exercise were performed with motor-controlled resistance using the new barbell. Unilateral GRF data was measured with a force plate under each foot, and the readings from each force plate are compared to each other. Results indicate the mechanical advantage barbell exercises have bilaterally asymmetric GRF compared to a theoretical 50-50 split, and the astronauts would need to alternate the left-right orientation to compensate for the asymmetry.