Why should you care about running form? Well, aside from reducing the potential to injure yourself, running is a series of thousands of steps, and with each step you take you expend a corresponding amount of energy. Over those thousands of steps you can overtake and run faster than a runner of equal ability, with less effort, if you pay more attention to form. This is also known as running economy. It's easy to work on, and is very rewarding to master. You will look and feel like an experienced runner, and in essence will become one much more quickly. You will also enjoy running a great deal more. We've all seen the average weightlifting-type that gets on the treadmill at the gym and pounds away at too fast a speed for five or ten minutes, making an awful racket, then gets off, huffing and puffing as he believes he has finished his "cardio" for the day. This picture I am describing is not intended to make fun of someone who is rightfully just trying to do what seems best. Many good runners don't have a clue of how to follow a proper weightlifting regime.
Running "form", or style, is in many ways a highly individual thing. There are certain components of running form that cannot necessarily be called "wrong", and are based more on opinion, and perhaps personal experience as well. A good example of the grey area of running form in which many esteemed coaches and runners alike differ in opinion is the positioning of the runner's arms - more specifically, the degree of arm bend and therefore, the height at which the hands end up. I am in the camp that believes in a higher, more compact arm position, particularly for long distance runners. Athletes that specialize in middle-distance events tend to use their arms more, and have them in a lower position - think of a sprinter, and you'll understand this difference. However, for most runners who will read this - those who enter 5km races and up to the marathon - my experience tells me that it seems to take a little less energy (and is maybe slightly more aerodynamic) to hold the arms at an angle that is a little tighter than 90 degrees at the top of the arm swing, with the hands near the chest, rather than a lower hand position that finds them along the sides of your shorts. I also believe that it takes a little less energy to hold the weight of the arms when they are higher up. Hold a weighted bar horizontally, and then slowly bring it up towards a more vertical position. Notice that there's less energy needed to hold the bar as you get closer and closer to vertical. In fact, if the arms weren't instrumental with balance and driving back to help maintain forward momentum, we would all have them completely bent to vertical and stuck to the front of our shoulders. The degree in which the arms are bent should be at their tightest when the hand is at its highest point, just before the arm drives back. As the arm moves back and the front of the arm lowers, the angle should relax a little, but no greater than 90 degrees.
A helpful way of looking at proper hand and arm position is to imagine that there are little elastic bands attached to your thumbs, with the other end attached to your corresponding nipple. Your hands should not move towards or away (on the horizontal plane) from the nipple it is "connected to" much more than a couple inches. Runners should certainly have a "driving backwards" motion with their arms, but it needs to be smooth, not wasteful. This is important - many runners have a "pulling" motion, in which they lunge each arm forward, and then back, as if they are grabbing some imaginary object that is helping propel them forward. This incorrect motion is often echoed in the legs - more on that later.
Once you have your hands and arms in the correct position, remember that there is only a driving back motion - the arm starts at the neutral point and then goes backwards, fairly sharply if the runner is moving quickly. There is no real forward segment - only a return to the start position. Think of it as driving the arm back, and then a return to neutral. As you perform the drive back, each elbow should move upwards as it moves back, not outwards (to the left and right). Remember, we are trying to be as aerodynamic as possible, and if your elbows are splayed out, this creates more wind resistance, not to mention forcing the shoulders to unnaturally move inward towards the neck over and over again, as well as likely forcing each hand to cross over to the other side of your chest - another common error in running form. The arm swing is a smooth swiveling motion. Remember the rubber bands? If you are moving your arms correctly, there should be very little horizontal or forward difference in the length between your nipple and thumb throughout the entire arm swing. If you move your arms too far forward, this length increases dramatically. If you splay the elbows out on the drive back, your thumbs will gravitate towards your outer rib cage. Visualize a smooth, parallel swivel that starts with your hands right in front of your chest, and not going forwards much at all, but simply swiveling your elbows backwards and up in a parallel motion, then returning to the start, remembering once again to not lunge forward. Don't push your chest out while doing this. All breathing in running comes from the belly area, or diaphragm, like a trained singer. If you are female and have taken Lamaze breathing classes in preparation for giving birth, think back to what you were taught in these classes, as proper breathing techniques while running are similar. The upper chest should not visibly be seen to expand! It all happens below this area. Breathing from the chest only allows more waste air to remain in the lungs, as they don't discharge this used air properly. Practice proper "belly" breathing, and you will run faster with less effort, since you will be getting more fuel (oxygen) in with each breath taken.
Your hands will, and should, move up and down, or vertically, as the arm swing occurs. At the top of the arm swing, the hand should be no higher than the shoulder. At the moment in which the elbow is behind the runner at its highest point, the corresponding hand should be no lower than the bottom of the rib cage. This entire range of vertical hand motion is not much, and should not be exaggerated. Remember to relax the hands, keeping them in a very loose shape that is halfway to becoming a fist. Your thumbs should be relaxed, but pointing up. This helps maintain the correct parallel nature of the arm swing. The hands should be loose and flopping up and down a little with the momentum of the arm swing. Relax your shoulders, and periodically drop your arms to shake out any tension that has built up. This shake-out is best done on downhill sections in a race, if possible, but can be done at any time. Remember, it is almost impossible for the arms to hold tension if the shoulders are relaxed. Arm tension starts in the shoulders, and works its way down. It is very wasteful on total energy output.
Once you have it all down, you'll feel efficient, and won't be wasting energy with unnecessary hand / arm motions in front of you, as so many runners do. Remember, everything that involves moving yourself forward in running starts at the spot directly under your centre of gravity, and behind you. There is nothing in front of your body that will help you go faster, or in fact move forward at all. This is very important.
Now, let's move on to the hips. Another very common, incorrect running posture that I see everywhere, and one that drives many coaches crazy, is the tendency to position the hips as if the runner is perhaps thinking about sitting down. Another way of visualizing this incorrect form is to visualize the body as something that can be "folded" in half at the hips. Think of being in a standing position and then reaching down to touch your toes. Now, in the running form example, think of perpetually being in the initial stage of performing one of these toe-touches. The rear end is sticking out a little, and the pelvis is slightly bent. This is not very good running form. You may have read elsewhere that it's a good idea to imagine that there is a string attached to your navel, pulling you along. This is the correct idea, but I like to expand on that idea a little and think of it as two strings attached to each hip, pulling you along. As you read this, stand straight and tall and thrust your pelvis outward, slowly, like a stretching motion. It is indeed a stretch, because you should feel your hip flexors being pulled tight. These muscles are your ally in running. They are the key to maintaining a tall body, completely un-bent pelvis, and ensuring you centre of gravity remains in the proper place. Further proof of this being correct running form is that you may notice as you tire, it's harder to keep the pelvis in its forward, frontal style - the poor runner will inevitably slip into the bent crouch, pushing their rear out and losing momentum through a weakened centre of gravity. What happens next is that this runner slows down. He will also have more difficulty breathing correctly, since it's the now crunched-up lower belly (diaphragm) that needs the space to move in and out, not the chest - remember the earlier part about proper breathing. Your lower belly needs space to do this.
Your legs are obviously the most important part of the body in running. They do the work, specifically the hamstrings (back of the thigh) and calves, although the quadriceps (front of the thigh) is called into action whenever a runner needs to run up a hill. Still, unless you are perpetually going up, it's the hamstrings in particular that do the lion's share. New runners generally develop their hamstring muscles at a faster rate than their quads, which unfortunately can create a muscle imbalance, leading to improper tracking of the tendons that surround the kneecap. Patellar Tendonitis and Iliotibial Band Syndrome are common for those newcomers, but can be avoided or minimized simply by following a set schedule, and not ramping up the mileage too quickly. Proper running shoes that are suited to the individual runner are a must, as well.
As I stated earlier, there is nothing in front of you that is going to help you go faster. This is especially true with the legs. Many runners overstride, and it's almost always caused by heel striking. Your feet should be landing directly under your centre of gravity. This is your hips. In fact, if you aren't looking directly down, you should not be able to see your feet at all. The degree of knee lift is proportional to two things - how fast you are going, and degree of incline. If you are not running up a hill, and you are moving along at a comfortable pace, there should not be much knee lift at all. Lifting the knee is lifting a weight. Don't do it any more than is needed.
A difficult part of the leg movement cycle to master is when the foot should be hitting the ground in relation to where it is in its cycle of motion. As I mentioned, many runners will overstride, making hard contact before the weight of the body can catch up, and this results in a perpetual braking action. You do not want to be landing on your heels. The heels should make contact with the ground, but only a split second after the forefoot. The forefoot (or ball of foot) should take the weight of your initial strike. If you overstride and heel strike, the strike of the foot itself momentarily stops forward motion, which the runner must fight through over and over again! No one wants this. Also, heel strikers are landing ahead of their center of gravity.
Although it's hard to master, try to already have the foot motion just barely (but already) on its way back just before it strikes. Don't strike at the end of your forward motion, then move back. I would argue that this one thing is perhaps the single biggest difference between an average runner and a good one. This is very subtle, but an extreme way of looking at it is imagining you are log-rolling. If you were trying to keep your balance while running in place on a log that is rolling in the water, you would certainly follow this principle! Another principle you would follow while trying not to fall in the water is a short stride rate, since there's a small area under you in which it is possible to place the foot. Remarkably, the log-rolling analogy applies here as well, since the place where the log would be is exactly under your centre of gravity.
I will expand upon this, as it's very important: Think of riding a bike - your foot is already on the way backwards when it is at the bottom of its cycle, which is the same moment as the footstrike in running. Work on this all the time, and you will get much faster, and reduce impact dramatically.
There should be three steps taken per second. Interestingly, this applies at fairly slow jogging speed, up to fairly fast running (but not sprinting). If you watch elite runners as they tire in the final stages of a race, they increase stride rate, not length. New runners will do the exact opposite, lunging each leg forward. As I pointed out earlier, this does nothing but create a braking action each time contact is made, and disrupts the foot strike under the centre of gravity. Employ little, short and quick steps when you are at the end of your next race.
So, once a runner has mastered the proper cadence of 180 individual steps or 90 pairs of steps a minute, and has very good form, what else can be done (aside from more training) to improve? Now the runner is ready to go back to what he/she avoided earlier, which is stride length.
Since stride rate generally should stay the same through a wide range of running speeds, at that point the only way to speed up is to increase stride length, which must be done without violating the rules of proper form, which dictate that everything happens behind the runner, and that overstriding is inefficient. When you see an elite Kenyan gracefully running sub-5 minute miles, he appears to be almost jogging. This is because his stride length is tremendous compared to an average runner, yet he does this while keeping the same form as if he were running much slower. He will not overstride, as he knows this is futile. Again, remember, everything happens behind the runner. All the power is not in lunging forward, but in pushing, or toeing off. As an efficient runner speeds up, his push off becomes more powerful, and another thing happens - the degree of knee bend when the leg is behind him increases, in many cases, dramatically. The secret here is similar to the degree of arm bend, and the weightlifting analogy that went with it. The lower leg is a weighted lever, and a runner lifts this lever thousands of times in a run. The higher the degree of bend after the push off when the leg is behind the runner, the less that the weight of the lower leg is stressing him over time. The higher bend also assists in continuing the explosive power of the push off.