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Saturday 22 September 2012

Running Fast - Slowly.


One of my biggest dilemmas with this article was the title - should you run slowly fast or should you run fast slowly.  Either way the outcome is the same.

Do you ever wonder how marathon runners can run at 3min/km pace whilst you struggle to run faster than 5mins/km ?  For most people to speed up, their strategy is to speed up their stride - their run cadence.  This is a similar logic to going faster on the bike ie pedal faster..

But cadence when running is finite so what happens when you 'max' out your cadence (the typical maximum is 200 steps per minute) and you are still no where near a marathon runners pace ?

Here is a simple exercise.

Run on a treadmill at what could be described as tempo pace.  This may be your 10km pace or what is sometimes called 'comfortable, uncomfortable' pace - a pace that is uncomfortable but you can maintain.  For me, who runs at a marathon pace of around 4:20min/km I use 16kph.

Now, running at that pace, slow down.  Before you reach for the speed control I am not asking you to change the speed on the treadmill - I am asking you to run slower at the same speed.  This sounds counter intuitive but is actually quite easy to do when you try.

So what are you actually doing ?  If your speed is the same but your cadence has slowed then one other thing must have changed.  That factor is stride length.  If you were to place a mark on the treadmill mat where the foot leaves the mat and another mark where it lands these marks would be further apart - this is stride length.

Now, lets apply so geometry to this.

Our run stride, when done properly, is a circular motion.  When a foot leaves the ground, travels in a circle and then strikes the ground (aka stride length) this path is called the circumference of the circle.  For those of you that stayed awake at high school you will recall that circumference is equal to the size at the widest part (the Diameter) multiplied by a constant called Pi.



So if we want to increase the circumference (stride length) we simply need to increase diameter ie we need to make the circle bigger.  This is achieved by controlling how high we lift the knee - simple.

Note the word 'lift' in terms of the knee.  We are not pushing off the ground as any force that moves the body upwards is a wasted force when our goal is to move forward.  One of the things I noticed when watching Sally McClelland win the Gold Medal in the 110m Hurdles at the Olympics was that she didnt jump over the hurdles - she simple appeared to lift her legs up from under her without changing the height of her upper body.  So make sure you focus on lifting the knee to increase the circle.  Your calves will tell you then next day if you have got this wrong...

Stretching, drills, plyometrics all help with improving stride length but I find the practise of running fast, slowly as described on the treadmill helps create the proprioception for doing this the best.

Or is it running slowly, fast.......

Tuesday 18 September 2012

Watts the Best Cadence ?




Over the course of Lance Armstrong's Tour de France victories his chief rival was Jan Ulrich.  Lance and Jan were opposites in many ways - one of which was their cadence.

Ulrich typically pedalled at a cadence of 80 rpm whereas Armstrong pedalled at 95+ cadence - even when on long, steep climbs.

Surely 'pushing' a hard gear would generate more power than spinning in a lighter gear ?

WRONG.

Let's look at some physics.

The measure of power is a Watt and in simple terms is the rate at which work is done ie work over time

Power = Work/Time

Ok.  So what is work ?

Work is the effort (Force) to cover a particular Distance.  In other words

Work = Force x Distance

So now that we know what Work is we can plug this back into the original formula

Power = Force x Distance/Time

Now a third concept - Velocity.  This is more commonly called speed and is what all athletes are seeking but within a speeding bike there are two other speed variables - the cranks (cadence) and the wheels (Rotational Mass (which is a whole different discussion on why wheel weight isnt the most important factor in wheel speed))

So Velocity = Distance over time (as in kmh or metres per second)

Velocity = Distance/Time.

If we plug THIS back into our formula we get

Power = Force x Velocity

So in order to increase Power we can increase Force (a harder gear) OR we can increase Velocity (Cadence).

Force is limited by the fatigue factor of the fibres.  As we progress to using more Type 1 fibres our rate of fatigue increases.  But if we use the same force and increase our cadence then our wattage goes up.

Think about your car.  When you want to accelerate to over take a car do you drop down a gear and increase RPM or go to a harder gear ?

If you look at the Tour Riders you will note they actually run very easy gears with guys like Contador running a 27 tooth cog on the rear.  This allows him to maintain a higher cadence when climbing.

A second consideration is run cadence (not an issue for Ulrich..)  Typically good runners use a cadence for around 188 steps per minute which is equivalent of a 'cadence' of 94.  By using a higher cadence on the bike more closely matched to run cadence a triathlete is better able to maintain a natural body rhythm .

Who said physics was boring.....