The great thing about running is that it you can never stop learning new stuff, like how to run downhill properly which is what I’ve had to learn recently. Sounds like something you don’t need a lesson in right? You just run, but…downhill. No. Apparently there’s a right way, and a way that is slower and could injure you.
When it comes to running downhill, too much leaning backwards is the issue, which acts as a sort of brake. This natural tendency to lean backwards, is a normal reaction though, since it slows you and stops you from running out of control. Running downhill forces your foot to strike the ground more towards your heel. This by itself increases braking forces, and a backwards lean magnifies this effect.
If, however, you do actually want to slow down, leaning backwards is the right choice. But since a downhill allows you a natural increase in running speed (since gravity is giving back all the energy you spent going up the hill), you generally want to take advantage of this. Ever wondered why you never seem to get the time back that you loose when running uphill? When you lean back, you throw your centre of gravity behind your body, requiring you to wait until your feet have passed it to start generating force again. Many runners apparently adopt this style of downhill running sub-consciously, it being a sort of mental brake first and physical brake second. Depending on how often you run on hills, this effect of hitting the ground with the heel, can cause injury through adopting poor running technique and also can lead to lower back pains through impact forces traveling up to the spine.
So in summary, unless you actually need to slow the pace, there seems to be little to gain from having a brake on going downhill, but what is the ‘right’ way in that case? The perceived wisdom with running downhill is to lean forwards very much according to the gradient, and balance with your arms and avoid heel striking. This allows gravity to work for you and aids more natural running mechanics so its generally going to be faster.
Naturally its important not to lean too far forward on downhills and as your speed increases, you’ll need to quicken your cadence to keep your feet underneath you. You’ll need to strike a balance between efficiently using the speed from the downhill and not running so fast that that you crash and burn. However like most things, this ‘balance’ of leaning forward and foot-stiking is something that you can learn and perfect, and is one of the things that keeps running interesting.