Plantar fasciitis is simply when this tissue is inflamed and irritated. After prolonged irritation it is also possible to develop a bone spur on the heel. When the fascia is strained, it usually becomes painful where the fascia is attached to the heel-bone. The heel hurts when walking, running, or even standing. It also hurts when the sole of your foot is stretched, for instance if you pull your foot and toes backwards towards you with your hands.
Friction is the cause of most black nails.
Friction from tight shoes, sudden stops and starts that jam the toe against the front of the shoe, or down hill walking that causes the foot to slide forward in your shoe. As a result, the toe repeatedly hits the end of the shoe, causing bleeding, fluid build up, and bruising under the toenail. In some cases the nail will discolor, with little or no pain. It is best to alleviate the problem and leave the nail alone. In most cases the nail will eventually fall off and regrow without any significant deformity.