In what old-timers refer to as ‘the glory days', the only people who continued to run beyond school were those who were born to be good at it. They didn't waste time discussing style. If you wanted to win, you trained hard. Injury was relatively rare and mostly occurred when you ignored the need for adequate recovery. But now, in a new and more glorious era where running is no longer the preserve of the elite, injuries are that little bit more common, and style is worth talking about.

The core principle of efficient running technique is to do just enough at exactly the right time to keep moving at the desired speed. Kids can do this through intuition - but as an adult you might need think about it - and doing so can get in the way of fluent action, and furthermore, the science can appear both frightening and contradictory.

The human body is complex and many of the details of running technique are controversial - but there are a several principles that have a strong scientific grounding. Put any fears aside and you will find the science of running makes everyday sense.

The body performs three key tasks when running at a constant speed: propelling your body forwards just hard enough to overcome the dragging effects that slow you down; lifting you into the air, which is essential if you want to go much faster than walking pace; and re-positioning your feet during each step so that they are in the right place when you need them. Let us consider each of these three tasks in turn, whilst remembering that it is a successful combination of all three that will lead to success.

Forward Propulsion

If you've ever slid your car on an icy road, you'll know that when there's nothing slowing you down, you keep moving at the same speed. When your foot is on (non-icy) ground in front of your body, the leg is angled forwards and downwards, exerting a forward push on the ground. The ground reacts by pushing back, causing a braking effect. You can minimise this by avoiding reaching forward with the swinging leg before footfall.

Here comes some physics. If your foot lands right under your centre of mass (located near mid-pelvis) and remains on the ground while you develop the thrust required to get airborne again, your body will begin to rotate forward and downward as it pivots around the point of support. Within a few steps you would hurt your face. To stop this you need to land a little in front of your centre of mass so that the oppositely-directed rotational effect that occurs when the foot is in front cancels out the effect when the foot is behind the centre of mass.

So to minimise braking and broken noses, we can only afford to spend a short time with the foot behind the torso, and indeed on the ground. We must balance cost of braking against the cost of getting airborne.

Getting Air

To propel ourselves upwards we must push against something - and the only thing nearby is the ground. When in contact with the ground (‘on stance') our foot exerts a vertical push. If you're aiming to keep braking costs low by spending (say) just a third of your time on stance, then that push needs to be hard enough to keep you airborne for two thirds of the time. To achieve this, the average vertical force exerted against the ground during stance must be three times your body weight. Therefore, unless you are prepared to endure a lot of braking, the vertical forces will be large, and you must prepare your body for this.

It's worth noting the some of the energy required to provide the upward push can be recovered from the elastic energy captured as tendons of the muscles controlling ankle, knee and hip are stretched at footfall. However, this elastic energy does not reduce the magnitude of the forces on your foot; forces that are transmitted through your legs to your spine.

Amazingly, your non-conscious brain is quite capable of estimating how long you need to spend on the ground to avoid a face-plant and to compute the required upward push after allowing for elastic recoil. It has been developing the necessary expertise since you took your first steps, and if you interfere you will probably get it wrong - though it is noteworthy that elite sprinters do consciously push.

Limb Repositioning

The faster you run, the further your foot gets left behind while on stance, and the greater the cost of accelerating the swinging leg to get the foot out front again. At high speed, it is best to fully flex the knee of the swinging leg because it is easier to swing a short lever than a long one. At slow speeds, repositioning costs are minor, but whatever, your speed, compact and tidy arms and legs avoid wasted energy. If you can keep your torso and head centred over the foot in the middle of your stance, this minimises the energy required to maintain your balance. And the less muscle tension and general flapping about, the better.

The energy cost of repositioning your limbs is paid for every step you take - and the rate at which you take these steps is called your cadence. At higher cadence, you can achieve the same percentage of time in the air with a smaller upwards push in each step. A large number of short hops use less energy than a small number of long hops for the same total airborne time. Unfortunately, lunch is never free when you mess with physics. Higher cadence means more energy spent on repositioning. When running at between 7-9 minutes/mile, around 180 steps per minute (90 on the right foot and 90 on the left) is the best compromise. At lower speeds the optimum cadence is a little lower.

A focus on running style is a good thing, and there’s plenty more to consider that’s beyond the scope of this article. In recent years we have seen a number of passionate schools of thought emerging: Pose, Chi, Evolution Running and others. Whilst they each have their own unique view on what constitutes an appropriate style, virtually all of the six key principles are accepted by all of these different schools. Irrespective of denomination, a good coach will have an expert eye for potentially harmful errors, so it’s usually well worth the time and money if you’re having problems. And if you are aware of the principles of good running and can ground them on good science, you are equipped to develop your own understanding and viewpoint on what constitutes good running style.