After the ride try to sit with your legs straight but without “locking out” the knees, a foot stool or floor cushion can be used.
Even better lay down and put a cushion under your legs so they are slightly raised, again keep a slight bend at the knees.
If the heaviness is in your thighs rather than calves, lay down and bend the knees to about 45 degrees, place hands either side of thigh (about 1/2 way towards hip), fingers towards knee and gently “wobble” the muscles by moving your hands about 6-8cm alternately (ie one hand goes clockwise while other goes anticlockwise, then reverse)
That sounds a bad explanation, I’ll try and find a link with some pics.