The effect of various types of support elimination (actual zero-g, water immersion, and head-down tilt) on the strength-velocity properties and tone of leg muscles was investigated. With all the exposures used, there was a high correlation between the tone decrease and the strength potential of antigravitational muscles, as well as the degree of support elimination (immersion and bed rest). This suggests that the tonic changes associated with the decrease of the support input are the major factor responsible for motor disorders during short-term exposures to zero-g.