The ornamental design for the exercise platform, as shown and described.
FIG. 1 is a perspective view of the exercise platform;
FIG. 2 is a top plan view of the exercise platform;
FIG. 3 is a bottom plan view of the exercise platform;
FIG. 4 is a front elevation view of the exercise platform;
FIG. 5 is a rear elevation view of the exercise platform; and,
FIG. 6 is a side elevation view of the exercise platform; the opposing side view is a mirror image of FIG. 6.
Areas within the broken lines in FIG. 5 form no part of the claimed design.
In the drawings, the evenly-spaced broken line showing of portions of the exercise platform depict environment and forms no part of the claim; the dash-dot-dot-dash lines define the boundaries of the claimed design and form no part thereof.