Rig is not animated properly



I got a rig where I want it to move its hands starting from 96 key. So frame 1 hands down and frame 96 hands up. In the meantime keys Maya can interpolate the moving up. It doesn’t do it. If I raise my rig’s hands at key 96 and I start my reel from frame 1, hands remain upwards. I want them to be down and gradually come up all the way from 1 to 96 frames. Why Maya won’t do that interpolation?