Time flies, and the Kalahari Augrabies Extreme Marathon
(KAEM) is getting closer. This means that there are many who are starting to
take a closer look at nutrition and in specific what to take with and how much.
I hope this entry will answer some questions for you.
The data was extracted from the Marathon des Sables (MdS)
2013 research I conducted.
Energy
There are a number of models that
can be used in determining an individual’s energy requirements. Among the
various approaches there is the Harris-Benedict equation, the revised
Harris-Benedict equation, the Mifflin St Jeor equation, Katch-McArdle formula
and the Cunningham formula, to name only a few. Various factors are taken into
consideration such as gender, heart-rate, body weight, activity etc. However,
their end result is the same, to determine an accurate figure that represents
the energy requirement for a person given a certain level of activity. What is
more significant is that all of these formulas deliver different results for,
essentially, the same set of bio-data. New research continues to refine the
calculations and with each step we are getting closer in determining a more
accurate answer.
But calculating energy is only
one factor in the energy requirement ‘basket’, other factors such as energy
conversion efficiency (which may differ from one person to the next), and an
individual’s ability to extract usable energy efficiently from fat reserves are
once again only some of the factors to consider. Biological functions such as
organ functions (including the brain), respiration and digestion all consume
part of the energy that is ingested. Stephen Seiler, in his 2005 book entitled
– Efficiency, Economy and Endurance Performance – notes that the efficiency of
converting available energy (from food) into mechanical energy (muscle action)
in humans are somewhere between 18% and 26%. Then the energy absorption rate
for different foods is also an additional compounding factor that could have a
huge impact on an individual who participates in an endurance activity.
With an energy conversion
efficiency of between 18% and 26% the energy requirement variance is
significant. If we assume 100% absorption for two individuals of the same
weight, gender, height, fitness level etc. with the one functioning at 18%
energy conversion efficiency and the other at 26% efficiency the energy
requirement would look vastly different.
Most of the formulas and
calculations make use of various factors that, to some extent, accommodate for
the energy conversion efficiency variance between individuals, but even with
these factors a median approach is followed. This means that given the best
calculation approach there will always be individuals who fall above and below
the ‘average’. I, therefore, turned to measuring the actual energy consumed by
the various MdS runners and related this to individual performance. I did
assume that the energy absorption for the diversity of foods consumed during
the event by the various individuals would be similar across the data sample.
What I found was that the
calculations has a significant margin of ‘error’ in that it over inflates the
requirement for an event like the MdS or KAEM. As these events are isolated and
differs significantly from ‘normal’ everyday life the results of the sample
data should not be applied to everyday life but should be limited to an
endurance event. Factors such as carbo-loading prior to the event and general
lifestyle prior to the event plays a role and should not be discarded.
Energy Requirement
The most comprehensive
calculation approach results in a broad view that an individual would require
around 44.11kCal’s per kilogram of body weight per day, of if related to a
250km race distance around 1.18kCal’s per kilogram of bodyweight per kilometre.
These calculations balance the high metabolic activity with a resting metabolic
rate to derive at a result. I was interested to see how this compares to the
runners in a real race environment.
At first I only looked at the
average for all men and women independently. From the initial data view woman
who had completed the MdS consumed only 37.1kCal’s per kilogram of bodyweight
or related to distance consumed 0.83kCal’s per kilogram of bodyweight per race
kilometre. Men on the other hand consumed slightly more at 37.9kCal’s and
0.85kCal’s respectively.
I then proceeded to view the data
in-terms of performance. Keeping to the top 10%, next 20%, next 40%, next 20%
and last 10% methodology which I started-off with at the beginning of this
series.
Position
|
kCal’s
per kilogram of body weight per day
|
kCal’s
per kilogram of body weight per race kilometer
|
kCal’s
per kilogram of body weight per day
|
kCal’s
per kilogram of body weight per race kilometer
|
Female
|
Male
|
Top 10%
1 to 100
|
34.7
|
0.78
|
40.7
|
0.91
|
Next 20%
101 to 300
|
40.7
|
0.91
|
37.9
|
0.85
|
Next 40%
301 to 700
|
29.4
|
0.66
|
38.6
|
0.86
|
Next 20%
701 to 900
|
40.8
|
0.92
|
36.0
|
0.81
|
Last 10%
901 to
1000
|
39.8
|
0.89
|
36.0
|
0.81
|
Amongst the male runners it seems
to indicate that the top runners consumed more energy than the rest of the
field. This, however, does not hold true for the female runners. What is
important to note here, is that the relationship between adequate energy input
and race performance continues to be supported. Men and women seems to respond
slightly different, men seems to respond positively to an increase in calorie
consumption whereas women seems to reach a performance levelling in relation to
an increase in calorie consumption much quicker. Yet again the figure seems to
be more fluid than expected, or indeed what I have hoped for.
Energy Consumption Variance within the Data Population
I then considered the minimum and
maximum variance amongst each of the performance groups. What this means is
that I identified within a particular performance group the minimum and maximum
variance given, from this I determined the average variance within the
particular group. The aim of this is to find the energy consumption across the
entire performance group. With this in-hand sufficient provision is made to
accommodate individual tolerance. This was done across the gender spectrum. With
this variance in-hand it is possible to extrapolate the particular energy
requirements for each performance group, taking into consideration the absolute
minimum energy consumed as well as the absolute maximum.
For both male and female runners
performance seems to decline once the optimal boundary is exceeded. On the
one-hand to little calories means that a runner might be running on “empty” for
large parts of the day. This would obviously impair performance. On the other hand
to much calories contributes nothing additional to the runners performance and
represents ‘dead’ weight as far as running weight goes. Please note I definitely
do not advocate cutting race weight by taking too little nutrition, as a matter
of fact I, personally, carry between 5 and 10% additional calories to ensure
that I have sufficient reserves to accommodate for any margin of error. In
previous years some runners have lost the trail and ended up running an
additional 10 or 20km on a particular day. For a 70kg male a 20km mistake,
based upon an optimal calorie count, would result in an additional 1,274kCal
(or 5,223kJ). If no reserve was included in the initial calculation this would
represent a substantial shortfall.
Psychological Effect
We must not discount the
psychological effect of nutrition. Perception pays as much a role as anything
else. MdS finishers were asked, after completing the race, whether they felt
they had enough calories during the race.
Amongst the top 10% of runners those
that fell below the 0.87kCals (male) and 0.63kCals (female) mark, all indicated
that they felt that they did not have enough calories. Amongst most other
finishers those that responded that they did not have sufficient calories seem
to have less tolerance for deficiency, here male runners indicate insufficient
calories at around the 40kCals mark (0.90kCals) while women mostly touched on
the 28.1kCal mark (0.63kCals). From this it seems as if women typically have a
greater perception tolerance, whereas men seem to respond negatively to
nutritional shortfall even when the shortfall is not realised yet.
Type of Food
Over the past two years I have
repeatedly seen exchanges between runners pertaining to the use of re-hydrated
food versus off the shelve food. During the MdS research runners were asked to
class their food stuffs. Amongst the group 48% indicated that they make use of
a mixture of re-hydrated and supermarket food, 46% indicated that they only
made use of re-hydrated food while the remaining 6% indicated that they only
took with supermarket food.
Post race a second question assessed
the runners own experience with the food they had taken. 73% indicated that
they had mostly the right type of food, 4% indicated that they had taken mostly
the wrong type of food while 23% indicated that the food they had taken was
totally the right type of food. What was interesting is that the only group where
100% of the respondents indicated that they had taken the right type of food
was the group that only purchased supermarket food. My personal view on this is
that it may be a case of familiarity. The dissatisfaction with re-hydrated food
may simply be that many runners don’t adequately test their food pre-race. This
has nothing to do with the actual food but rather, relates to personal
preference and how an individual’s body responds to nutrition.
The survey neglected to ask
whether food was tested prior to the event and to what extent it had been
tested. Hopefully this can be assessed during the 2014 MdS which may provide
more clarity on the issue.
Food Group Composition
Fat, Protein and Carbohydrate
composition seems fairly normal across the entire respondent sample with
Carbohydrates coming in at 67%, Protein at 25% and Fat at 8%. There were some
notable exceptions among these, the following might be noteworthy.
Race Position
|
Protein
(%)
|
Fat
(%)
|
Carbohydrate
(%)
|
Top 10 Position
|
20
|
25
|
55
|
Top 300 Position
|
25
|
20
|
55
|
I am aware that it is problematic
to deduce or infer anything from such an insignificant sample, so no claim is
made as to the link between performance and food composition. What is
interesting, however, is that both runners had a significantly reduced
carbohydrate diet (12% less than the usually recommended norm, yet both
completed the race and one, at least did so with a high level of performance).
This warrants additional research and I hope to identify a larger group of
predominantly fat / protein based runners whose performance can be tracked.
Sports Drink
Not all runners take sports
drinks during a race or event. During the MdS 65% of finishers did make use of
sports drinks during the event while 35% drank only water. There is no clear
indication that links sports drinks during the event to performance.
Amongst the runners who did make
use of sports drinks 57% drank it throughout the day, 34% only drank it at the
end of the day, 7% at the start of the day and 2% when they felt they needed it.
Even among this group there is no noticeable advantage that links drinking
methodology to performance.
Carbo-Loading
57% of MdS runners did carbo-load
prior to the event while 43% indicated that they did not. The type of
carbo-loading was not determined. Those that make use of carbo-loading are
spread throughout the field as is the group that don’t. Even among the top
runners there is no conclusive trend that links carbo-loading to performance.
Unfortunately, what is understood by the term carbo-loading might also play a
significant role in the responses. As many of the runners live on a
predominantly carbohydrate based diet, they are in actual fact carbo-loading
although they don’t interpret it as such or actively set-out to do so. I do
suspect that once the concept of carbo-loading is better defined we might find
that a much larger percentage actually engage in the stocking-up on
carbohydrates.
Sodium, Potassium and Hydration
During events like the MdS or
KAEM most runners and all medical personnel is acutely aware of dehydration and
sodium depletion. This is actively managed and to a large extent supplemented
through the sodium content of race food. Often the sodium intake through food,
sports drinks and snacks provide more than sufficient sodium so addition sodium
intake through tablets may not be needed.
Water will always be in short
supply and some level of dehydration is expected, this is why these events is
classed as extreme. It is, however, not the lack of water that causes many
runners to become dehydrated but rather their water intake regime. Many of the
runners who became dehydrated did not drink constantly during the day but drank
large amounts of water at the check-points.
Potassium on the other hand is
not that easily recognised and managed. Many of the symptoms associated with
potassium depletion and/or even reduced potassium levels are similar to sodium
depletion and dehydration. The notable exception is that once a race is over
runners return to a normal eating regime whereby hydration is paramount and
sodium levels are increased through normal food intake. Sodium levels stabilise
and return to normal, as do fluid levels, this typically happens within a day
or two. I therefore asked runners during the post-race assessment to indicate
whether they continued to experience, up to two weeks after the event, a number
of symptoms, all of which are the typical symptoms that is associated with reduced
sodium levels and dehydration.
A total of 4.4% of finishers
continued to experience typical dehydration and reduced sodium level symptoms up
to two weeks after the MdS. However, there are a number of very significant
symptoms that need mentioning: 14% indicated a general feeling of depression,
10% a general lack of energy, 12% leg severe involuntary muscle cramping during
the night, and 27% reported sleepiness and tiredness.
Without additional testing such
as blood-tests, urine analysis and ECG to name a few possible measurement
methodologies, it would be impossible to definitively state that extreme
runners experience a significant potassium level decline, however, the post
symptoms provides a strong indication that this may be so. Additional research
would be required to confirm my preliminary observation. In the meantime
extreme and ultra-endurance runners would benefit from supplementing their pre-race,
race and post-race diet with potassium rich foods.
Conclusion
There are a number of elements
that remains unanswered and requires some additional research before a definitive
answer can be given, however, from the available data the energy requirement
spectrum for both males and females seems well defined. What every individual
must determine beyond the basic physical element of the energy requirement
spectrum is at what point does the feeling of hunger, or the perception of
having inadequate food intake, impacts negatively upon him or her as an
individual. This is not as easily quantifiable and is a very personal element
in the equation.
Thank you for reading my blog and
see you soon.
Genis
