An inertial exercise device includes a hollow outer ball and a weighted inner ball elastically suspended inside the outer ball by at least two opposing suspension members. The weighted inner ball may contain a fluid mass. The hollow outer ball, the weighted inner ball and the at least two opposing suspension members may all be integrally formed with each other. In one embodiment, the outer ball, the inner ball, and the suspension members are all formed from integral segments of a pliant tube. The hollow outer ball is formed by everting first and second end segments of the tube over the middle segment of the tube and joining the first and second end segments of the tube together at their openings. The weighted inner ball is formed from the middle segment of the tube which, in one embodiment, is a bulge in the tube.