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Monday, 27 June 2016

The Whyometrics of Plyometrics

You'll often seem me in the local gym jumping from foot to foot or over benches.  Apart from giving the meat-heads something to snigger at what am I actually doing and why ?  It's called Plyometrics.  Whilst the term plyometrics is accredited to the US runner Fred Wilt, plyometrics themselves were originally created by the Russian Yuri Verkhoshansky in the late 1960's, early 1970s.  Over the years a huge number of studies have found benefits to runners and triathletes in doing plyometrics (and that doesn't include for the amusement of others)

Ground Contact time.
The most efficient part of running is when the runner is in the air.  When the runner is on the ground as part of the stride, braking forces via friction are applied and the runner's movement is slowed.  If this ground contact time is reduced then this loss of momentum is also reduced and runner moves more efficiently.  In simple terms plyometrics reduces the time between landing and leaving - from a physiology perspective what this means is reducing the time between the eccentric (lengthening) and concentric (shortening) phase of the muscle movement.  It's important to remember this - we are trying to reduce the rebound time.  So when doing plyometric exercises it's important to mimic this.  For example jumping over a bench or box isn't strictly a plyometric exercise.  Jumping over a box or bench and then IMMEDIATELY jumping straight up and trying to touch the ceiling IS a plyometric exercise as we trying to reduce the time between eccentric and concentric contractions. It is therefore important when doing plyometric exercises to try and minimise time between landing and leaving the ground.

Plyometrics also help improve the elasticity of tendons.  When running, energy is stored within ligaments and tendons (kinetic energy) - plyometrics help improve the storage/release of this energy which further assists in 'spring' and in reducing ground contact time.

Some of the new Garmin watches like the 920XT and 735 measure and record ground contact time so it's easy to track improvements.

Stride Length.
In simple terms running velocity is cadence (how many times you turn your legs over per minute) multiplied by stride length.  Reducing ground contact time improves or increases cadence but there is a finite improvement and generally this is around 195-200spm (steps per minute).  Once cadence is optimal the only way to become faster is to increase stride length (and conversely when stride length is optimal the only way to become faster is increase cadence).  Beginner runners may have a stride length as low as 30-40 centimetres whereas Olympic marathon runners can be up to and even in excess of two metres (and they are typically not very tall either - their stride length is greater than their height).

So how does jumping around improve stride length ?

One of the biggest limiters to stride length is joint range of motion mostly around the hips and hip flexors.  Some people call this flexibility but whatever the term the issue is the same - lack of hip range of motion greatly impacts how long a stride you can take.  Plyometrics facilitates Dynamic Stretching (not to be confused with Ballistic Stretching which can be dangerous).  Dynamic stretching involves taking a muscle (or joint) progressively out to it's full range as opposed to Ballistic which can take a joint or muscle beyond it's range.  Dynamic stretching is more effective than static stretching too as it over-rides the brain in restricting muscle range via the golgi reflex.

For runners, plyometric exercises such as split lunge jumps dynamically stretch the hip flexors and glutes to quickly improve Range of Motion.  Split Lunge Jumps involve standing in a lunge position, jumping up in the air from that position, swapping legs in mid air and landing in the opposite lunge stance.  As mentioned above you then want to immediately jump and swap back to the original lunge position.

Injury Prevention / Support Muscle Recruitment.
Many injuries including the common ITB issues are caused by support muscle activation (or lack of).  Unfortunately a lot of physio exercises are focused on muscle strengthening rather than activation.  For example side leg raises are great for strengthening the glute medius muscle (which helps stops the knee dropping in and aggravating the ITB) but does little to help with ensuring the muscle 'switches on' at the right time when running.  By forcing the body to try and stabilise itself (or fall over giving the meat-heads further things to snigger about) plyometrics cause subconscious activation of the support muscles.

Rather than doing leg side raises for the glute medius I recommend lateral hops. Stand on one leg.  Hop to the opposite side as far as possible and land on the other leg.  Hop back.  If it takes you a long time to stabilise/balance it's a good indicator that your stabilising muscles aren't working or activating very well.

So whilst they look trivial and are often the sessions people 'miss' (funny how an athlete will get up at 4am and run two hours in the rain but are too 'busy' for a fifteen minute plyo session) plyometics can add more value than simply just running more and in a much more time efficient manner.  

What are some of my favorite plyometic exercises for runners ?  Here are a couple :-

- Split Lunge Jump (as mentioned under stride length)
- Lateral Hops (as mentioned under Injury Prevention)
- Jump down box springs (stand on a box or bench, jump down and on landing immediately jump up and touch the ceiling)
- Box Hops. (Standing on one leg hop forward towards a box and then immediately hop up onto the box)

Rather than reps it is better to use time ie complete as many reps of an exercise in sixty seconds.  This also facilitates increasing the speed at which you are doing the reps which, in turn, makes the exercise more effective.

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