The Science of the finishing kick

Kicking it into gear.

I’ve explored the phenomenon of the kick a little before but with recent research and with the fact worlds has just happened, let’s explore the kick phenomenon a bit more.  First, let’s look at what actually happens physiologically, and then what we can do about it.

The physiology of the kick:

Energy systems dynamics:

An interesting new study sheds some more light on why we might be able to run faster, particularly at the end of a race.  You can read about it here (LINK) but they took cyclist and had them do either solo time trials or against a computer which was really their previous selves.  What they found was that when racing someone, they were able to increase their speed and the sole reason was the anaerobic energy component.  In other words, the cyclists used the same amount of energy aerobically, but in the faster trial they were able to tap into more of their anaerobic capacity.  This has implications in regards to motivation which we’ll discuss shortly, but for now lets look at what this and other research means for the kick in terms of energetic.

If we define the kick as the last 100-400m or so of the race where the pace is increased you have to look at two factors in terms of what effects the kick.

1.     

  How we got there- If we look at things in terms of energetic, the person who gets to X point in the race when it’s time to kick the most economically will be in best position to tap in his energy reserves.  If we think in terms of energy systems, this could be the person who is most aerobic at X point.  Looking at lactate, previous data has shown us that some elite Africans tend to get to this X point with lower lactate levels then their counterparts.  What that means is that they haven’t used as much anaerobic energy to get to the point, thus they have much more in reserve to throw it down.  This reason alone is why “faster” pure speed athletes sometimes can’t kick.  They may have better speed, but they’ve used all their “speed” (and anaerobic capacity) just to get to that point, so when they try and go, there is nothing left.

2.     

  How much we got left- Given the above, there’s another factor that plays a role energetic wise.  How big that anaerobic energy tank is.  Someone could get to the X point the most economically, but if he has a very small tank of anaerobic gas to use, he’s still not going to have a good kick.  If we think in terms of lactate, then having an ability to increase their peak levels to a high amount at the end of the race is critical.

So for the ultimate kick, the idea energetically is to get to the point X as efficiently as possible and having a big tank of anaerobic energy to throw down that wasn’t tapped into during the race.  If we think in terms of lactate, it’d be having a low lactate at X point then being able to jack it up to a really high amount at the end of the race.

Motor unit recruitment

                Another similar factor that has been studied is motor unit recruitment.  This ties into and is similar to the above energetic model.  If we look at studies on kicking, they show that the increase in speed is directly related to an ability to increase muscle motor unit activation.  It makes sense.  The more motor units we can activate, the more power/force we can produce.

                Once again, this is like energetics. As we fatigue during a race, we have to call in more and more muscle fibers to do the work and we have to cycle them through faster.  If we’ve cycled through everything when we reach our X point, then there’s nothing left to access and we have no way to increase force production.  Therefore the goal is to be able to be very efficient in terms of muscle fiber use getting to point X, and then having an ability to access a large number of motor units at the very end.  So once again, the goal is efficiency to point X, then having the neural ability to recruit more fibers.

                If we look at some past studies measuring EMG, there’s a clear correlation between the increase in speed during the kick and the increase in EMG signal, or motor unit recruitment.  Being able to send a stronger neural signal to recruit more fibers is key during the kick.  How’s that done? By having the neural pathway ingrained so that you can access it, and by having sufficient “motivation”, which we’ll discuss shortly.

Biomechanics- ability to change gears (strides rate/length)

                These ideas all tie together to a larger degree and one of the results of the two above mentioned factors can be reflected in the stride mechanics.  There are two ways to increase speed.  Either increase stride rate or stride length.  Each runner tends to have their preferred way to do it to a degree.  Some are more length dependent, some more rate, and some a nice mix of both.  Everyone uses both ways, but the exact combo depends.  What’s interesting is that when we pick up speed to kick, something has to change, and that for the most part, people tend to increase via whatever way they haven’t maxed out during the race.  So if they’ve kept their stride length slightly lower and relied more on a high stride rate throughout, then they’ll jack up the stride length, or vice versa.

The bottom line is we have two ways to increase speed and it’s best to have both at each of our disposal.  If you have two ways to go, then you’ve got an out if you are so fatigued that you can’t increase stride length for example. A good example of this is shown in this data from the 2007 world championships:

http://www.scienceofrunning.com/2010/11/speed-stride-length-x-stride-frequency.html

               

Motivation

                Lastly but certainly not least is the issue of motivation.  The aforementioned study on the cyclist also points out a seemingly obvious but subtly important issue.  When we have competition or are motivated, we can improve our performance.  That’s a no brainer right?

                But what’s interesting is how.  We always have stuff in reserve.  Our body is too well controlled to let us push so deep that we risk injury or death (my boss Alberto Salazar might be the only exception here…).  So it has all sorts of safety mechanisms to shut us down  (or fatigue us) before we reach that point.  One of the most obvious is once we get near deep fatigue, the brain might start shutting down muscle fiber recruitment.

                What’s interesting is that motivation, or importance, changes this equation slightly.  It lets us push just a bit further.  In essence, our end “governor” point is extended just a bit.  The extreme example of this are those stories where you hear some lady lifting a car to save their child or someone lifting a big boulder to save someone.  These are feats of superhuman strength where our bodies have essentially weighed the risks and decided risking muscle/bone rupture/breaking is preferential to death in most cases.  So, the limiters are gone and boom, we have super strength.

                The same thing happens to small degrees in races.  If we are highly motivated, if the competition means something, and if we are in the thick of things and believe we can hit some goal, then we’re more likely to be able to extend that governor and call upon a stronger kick.

What’s it all mean?

Get to the end more aerobic than anyone else

Have a larger degree of anaerobic capacity to use.

Have a large reserve of motor units you can call upon

Be able to use them in fatigue!

Be close enough and feel good enough where your body extends it’s limits a little- be motivated and challenged with goals just far enough to challenge yet close enough to be achievable.

How to train a kick?

This will be the next follow up post. And here's my heavily biased favorite kick for a guy who sucked at kicking for a few years...:

Watch more video of Ryan Dohner on flotrack.org