Bolt vs Farah at 600m. The extremes meet, who wins?

Bolt vs Farah over 600m: The extremes meet in the middle (kind of, physiologically...)
For athletics fans, the prospect of Usain Bolt vs Mo Farah over 600m
an enthralling spectacle where the most dominant athletes at the
extremes of track
running test themselves with one foot in the other’s domain.  I suspect
it is highly unlikely to happen, but it's a great platform for some
debate around performance physiology.
Predicting the winner is a fun exercise in stats, performance
analysis and physiology (performance analysis - it's not an exact science, remember!).  
fascinating question for this one is where do the physiologies of these two “extreme”
athletes cross?  Of course, bear in
mind that there are athletes in the middle who would arguably beat both
Farah and Bolt over 600m, and by a long way.  When David Rudisha broke
the 800m WR in London last year, his 600m split time was 1:14.3, and
that's about as fast as I suspect Farah or Bolt could run in a straight

Rudisha's 1:40.91 predicts something
under 1:12 for 600m (the world record is 1:12.81, and that's from Johnny
Gray, who was 1.6 seconds slower than Rudisha at his best), so he would
certainly win a 600m were he in it.  In fact, so would just about the
entire men's 800m Olympic final field, and a good few 400m, 400m
hurdlers and 1500m runners (the 800m/1500m combo guys) too - this 600m
is not about finding the best athlete, but about some fun and publicity!

Physiology at the 'extremes'
Physiologically, making the prediction invites some discussion over the origin and capacity of the energy pathways used
by each, and what it means for fatigue. 
It boils down to different questions for each man.  For Bolt, it’s whether he can withstand
the fatigue of going three times further than his normal race distance, and how much
he would need to slow down to avoid complete failure to even finish the distance?
For Farah, it’s whether his top speed
is high enough to pressurize Bolt into that premature fatigue? 
A quick physiological lesson will explain:  When you see athletes tying up and
slowing down dramatically at the end of a sprint race, what you are witnessing
is the combination of a "failure" of energy production (the supply can't meet the demand), a build up of
metabolic by-products in the muscle and the central and peripheral responses to these changes. 
Nobody knows the full explanation for this, and it’s likely more
complex than any current theory can explain, but the result is a
reduction in muscle contractility with sub-maximal muscle recruitment.  
Studies have shown, for instance, that at the end of a 400m race,
drop-jump performance declines by 39% and that muscle activation
increases, which shows the cumulative effects of fatigue on muscle
function - more recruitment needed for less force/power.  Other studies
show that this happens despite pacing, and the presence of some muscle
unit reserve, which implies that fatigue occurs partly in the
brain, partly in the muscle.
The source of energy is crucial to both fatigue processes, because it
affects the biochemical changes occurring in the muscle.  Bolt and Farah
rely on different pathways for their energy.  Bolt has a highly developed pathway that produces the energy
needed for muscle contraction very rapidly, but not for very long.  His energy comes primarily from what are
known as oxygen independent (or anaerobic, though this word is avoided by many) pathways.  They are all about the speed of energy supply, and the consequence – a build up of
metabolites, is an accepted downside because he doesn’t need more than 20
seconds of explosive power. 
Farah, on the other hand, can produce energy for hours, but
more slowly, using primarily oxygen dependent, or aerobic pathways.  The
upside is less peripheral accumulation (though glycogen depletion is,
eventually, a theoretical 'limit'), the downside is the rate of supply.
 This difference accounts for the clear differences in the optimal
pacing strategy between short duration and long-duration events,
something I summarized in this review article for BJSM.
There is always an overlap, with some contribution from both pathways, no
matter the distance, but for shorter, high intensity exercise like sprinting, the
oxygen-independent pathways are more heavily relied upon (in the 200m event,
for instance, the split is around 70%-30% in favor of energy production without oxygen.  By 1500m, it is reversed to 30%-70%). 
So, as much as Bolt and Farah lie at the opposite ends of
the performance spectrum, they are also extremes of biochemistry.  Muscle histology and function also differ – Bolt’s are
more contractile, able to contract rapidly and forcefully, but they also
fatigue more rapidly.  
The prediction
Over the nominated distance of 600m, Farah would be forced to
find a force and speed of muscle contraction and energy production that he is
unfamiliar with, while Bolt will be asking his biochemistry to withstand an accumulation
of metabolites and resultant fatigue that he is also unaccustomed to.
As for a prediction, the biochemical odds are slightly
tilted in Farah’s favor at 600m.  A
number of people have attempted to model where the perfect distance is, and
using the above-mentioned energy pathway models, have estimated that the
perfect distance, with equal performances, lies somewhere between 500m and 550m.   
Those additional 50m, seemingly
trivial, probably just give Farah the edge and represent 50m too far for Bolt’s
physiology.  Farah’s famous
finishing kick, as well as his recent 1500m performance, a European record of
3:28, have shown that he has extra-ordinary sustained speed for a distance
runner, so the biochemical “jump” to a 600m may not be as large as the step up
from 200m to 600m for Bolt. 

On that performance note, Farah's 600m
performance is easier to predict and is more familiar to him - it's
something he'd do regularly in training, whereas Bolt would very rarely
approach even sub-maximal efforts for this duration.  

Performance-wise, Farah's 3:28
suggests that his 800m performance would be in the range of 1:45 to
1:46.  That would optimally be achieved with a 51-52s first lap, and a
53-54s second lap.  That in turn suggests that a very fast 400m of 49s
would be possible.  Then it becomes a question of limiting the slow
down, and finishing with a time around 1:14-1:15.  It's about starting
fast enough to take advantage of sustainable speed and attenuated
slowing down at the end.
Bolt, on the other hand, has to worry about the opposite problem - not
starting too fast.  He has run 400m in under 46s almost every year
since 2007, including a PB of 45.28s six years ago, and a 45.35s at the
age of only 17.  So he may have the
natural ability, if he judges the pace well, to edge Farah.  However,
six years is a long time, and those low 45s are probably less relevant
now, particularly since he has probably gained mass since 2007.  Mass
hurts over longer distances, so Bolt has this to deal with as well.  If
Bolt does go out in 48s, gaining an advantage of around a second over
Farah, he'd need to hold on to around 27s for the final 200m, and I
suspect that would be a little too much to ask.
With a month of dedicated training for
the 600m distance, my money would be split.  In my opinion, it would be a
coin toss - Bolt would be able to change the training enough to adapt
just enough to make it incredibly close.  But, if the race were to
happen straight after their specialized seasons, Farah has the edge.
 I'd pick Farah by about half a second to a second.  Over 550m, maybe it
comes down to the lean.  It would be a fascinating
meeting of two extremes.  It would sure be fun to watch, and discuss -
that happens over on Twitter and Facebook!
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