“Hitting the wall” – a closer look
A running body operates on much the same principles as a running automobile. There is a fuel which undergoes necessary changes to release energy. This energy is used to produce motion – be it for an automobile or a runner. Given this construct, it all comes down to a simple equation – (i) how much fuel can a body store vs. (ii) how much fuel does the body need?
Now for relatively smaller distances (say up
to HM), the fuel that the body can store is sufficient to power the entire run.
However, as one migrates to longer distances, the finite nature of body’s storage
capacity becomes evident. Let us explore this a little more closely by looking
at both sides of the equation:
(i) How much fuel can a body store?
- Carbohydrates are the main energy producing food. When we consume carbohydrates, these are broken into glucose and glycogen. Glucose is absorbed in the blood and circulates through the body – this is the most readily usable form of energy. Whatever energy is not needed immediately is stored in the form of glycogen reserves.
- There is a limit up to which a body can store glycogen. Different studies have revealed that a healthy human body can store up to 550 gms of glycogen (when appropriately carb-loaded).
- In energy terms, 1 gm of glycogen corresponds to around 4 kcal of energy.
(ii) How much fuel does a running body
need?
Clearly, the
amount of fuel that a runner needs can be a function of multiple things. It
can depend on aspects such as runner’s weight, running form, running economy
etc. Even for a given runner, it can vary depending on the pace at which one
runs. It is fairly intuitive that running at a faster pace would require
greater fuel consumption as compared to running at a relaxed pace. Different
studies have revealed that a runner typically needs around 3 to 4 gms of glycogen per min of running.
Understanding this
fuel consumption rate for an individual runner is critical as it has
implications in terms of when the runner may possibly hit the wall. This is
fairly simple and can be computed by using typical running watches. All you
need to know is the calories burnt and duration of run. For instance, following
figure indicates how I can use the data from my TomTom watch to compute my fuel
consumption rate for a fast run (say ADHM 2015 which is my PB for a HM) and a
fairly relaxed pace (say closer to a full marathon pace):
A couple of obvious interpretations from this analysis:
- When I run fast, the fuel consumption rate increases. For instance, at a pace of 4:18, my fuel consumption rate is around 4.1 gm per min (as compared to 3.4 gm per min for a pace of around 5:34).
- Even if I run at a slower pace of 5:34, my fuel reserves (assuming ~ 550 gms) will only last for 162 mins (=550 / 3.4). In that time, a pace of 5:34 would have only taken me to around 30 km mark!! This is well short of 42.2 km mark that a full marathon requires me to cover. In the absence of appropriate fueling during the run, I face a risk of hitting the wall around that time.
This analysis
highlights that there is a finite glycogen storage capacity for a human body
and if the body needs to run beyond what this finite fuel can power, it has to
rely on other fuel sources. This can come in the form of either burning fat
(which is not ideal as burning fat requires significant oxygen intake, which is
sub-optimal) or it can come in the form of replenishing glycogen reserves
during the run (through during-the-run fueling). Let us look at this second option
a little more closely.
Replenish the reserves during the run
The first
step to understanding ways to replenish the reserves is to understand the “fuel
gap”. Looking
at the numbers from the analysis above, a pace of 5:34 would require me to run
for a around 3 hours 55 mins to complete the full marathon. During
this time, a fuel consumption rate of 3.4 gms per min would require me to
consume around 798 gms of glycogen. Given
that a healthy human body can store only around 550 gms I have a deficit of
around 248 gms of glycogen, which I need to replenish (to be reasonably assured that I won’t
hit the wall).
Consuming power gels, bananas, energy bars, nuts and sports
drinks during the run are some of the most commonly used ways to replenish the
fuel reserves. Understanding the carbohydrate content in some of these common
during-run foods may help one develop the right fueling plan.
In the figure above, I have listed the carbohydrate content of the fuels that I usually carry for my long runs.
Overcome the wall
Why “hit the
wall” when you have the option of “blasting” it through simple fueling related
precautions! In more serious terms, one can certainly push the wall beyond 42.2
km mark by ensuring right fuel intake during the run. The key is to keep fueling the body before it is too late (remember – don’t wait for the fatigue signals to start fueling – by then, it may be too late).
I have thought through
the fuels I plan to carry for SCMM full marathon in a couple of weeks. Have
you?
Sundeep Singh
Sundeep Singh
+91-98181 19794
------------------------------------------------------------------------------------------------------------------------------------------
About the Author: By background, Sundeep Singh is a Mechanical Engineer from IIT Delhi and holds an MBA from IIM Kozhikode. Given his flair for mechanics and passion for running, he loves to analyze and write about the finer nuances of running techniques / strategies.
