You may have never put an ounce of thought into it, but how your foot hits the ground when you walk or run has a lot to do with your performance and the likelihood of becoming injured over time. Basically, there are three foot striking scenarios:
Heel Striking: This is a very common way for people to land on their feet is by striking heel first, then rolling down to toes. This is widely considered to be very detrimental to performance and to joints (especially knees). This striking pattern is a lot like hitting the brakes with every step. By doing this you are momentarily stopping forward momentum until the rest of you catches up. This method of foot striking is mostly blamed on wearing thick shoes. If you ran like this barefoot, it would hurt very badly, but with a nice cushy sole underneath your heel, you can do it just fine…for now.
Notice the difference in this picture where the first child is wearing shoes and the second one isn’t. Notice the graph on the left where you can see a dip in momentum where the heel strikes.
This foot strike doesn’t incorporate your plantar fascia (the bottom of your foot) very much, leaving that to become weak and over-stressed easily over time. It also sends a lot of shock to your heels, potentially causing heel spurs, and to your knees, shocking them into hyper-extension with every step.
Midfoot Striking: Not landing flat foot, but landing behind the balls of the feet. This gives your ankles a chance to help take some of the pressure off your knees and absorb some shock. When you land further on the front of your foot, your foot lands closer to your center of gravity, preventing over-striding (extending beyond your center of gravity).
Contacting the ground underneath your body keeps you from putting on the brakes with every step and keeps your momentum forward, keeps shock off the knees, and gets your plantar fascia working.
Just look at this beautiful example:
Forefoot Striking: Landing on the balls of the feet. Again, similar situation with mid-foot striking.
The ability for the foot to absorb impact is called impact transient. In the heel strike you see it quite profoundly:
Basically though, most experts agree that avoiding over-striding is one of the most important things you can do. Take smaller steps right underneath your body and your feet and knees will naturally correct themselves. Also, landing softly on your feet, however you strike, is of the utmost importance. Your feet should never, ever slap down. You should always be in control of your feet.
If you’re adjusting your stride or foot slapping, you will get tired faster because you will be using more effort to walk or run, but that’s the whole point. The patterns of movement that cause injury are generally caused by doing it the ‘easy’ way instead of the proper way. Start slowly at first until your body gets stronger, and it will, and not only will you be injury proofing yourself, you will get stronger and faster as a result.