A biomechanical comparison of 1-G and fully loaded simulated zero-gravity locomotion.

摘要

Ground reaction forces, muscular activations, and joint angles of the leg during overground, treadmill, and fully-loaded zero-gravity simulated locomotion were assessed in order to gain insight into the effectiveness of the exercise regimen used by NASA to prevent the muscular atrophy and bone demineralization which occur in weightlessness.; The Zero-Gravity Locomotion Simulator (ZLS) is a device which suspends subjects horizontally from multiple latex cords. A treadmill mounted on the wall under the ZLS enables subjects to run in 0G simulation. The Gravity Replacement System is a set of springs connected to the subject via a harness which act to tether the subject to the treadmill.; Sixteen individuals were studied at two speeds (1.35 and 2.68 m/s). Data were collected during overground locomotion, standard treadmill locomotion, ZLS "shoulder springs" locomotion, and ZLS "waist and shoulder springs" locomotion. Ground reaction forces were assessed using a force plate mounted within the ZLS treadmill belt and another mounted in the laboratory floor. Angles of each subject's left ankle, knee, and hip were measured with electrogoniometers. Electromyographic data were collected of each subject's left tibialis anterior, gastrocnemius, rectus femoris, vastus lateralis, biceps femoris, and gluteus maximus muscles. Spring tensions were measured in the ZLS conditions using load cells mounted at the spring attachment sites on the treadmill.; Maximum ground reaction forces were significantly less but loading rates greater in the ZLS conditions than in the overground condition. The knee was in a significantly more flexed position during the ZLS conditions. The positions of the ankle and hip were similar in all conditions. The activations of the tibialis anterior, rectus femoris, and vastus lateralis were greater in the ZLS conditions, while the activations of the gastrocnemius, biceps femoris, and gluteus maximus were unchanged.; Subject discomfort from the harness and fluctuation of the tethering load are believed to be related to the above differences. Tethered treadmill exercise should prove to be an effective countermeasure against muscle atrophy in space. Its effectiveness towards preventing bone loss is dependent on whether it is the maximum force or maximum loading rate which controls bone remodeling.