Striking

Where your feet land when you strike the ground can determine your running form.

Old-school running can include heel-striking by which your heel is the first part of the foot to come in contact with the ground upon stepping down.

Nowadays heel-striking is frowned upon for its detrimental effects such as instigating shin splints (hell, as previously mentioned). It creates a line of impact that travels through the heel and lower legs, jolting up into the hips.

A terrible side-effect is plantar fasciitis or fascia. Essentially, heel-striking can cause painful irritation of the muscle that runs along the bottom of the foot, triggering a pain when the heel hits the ground (even just walking) like a stabbing.