If
you've ever run a marathon in warmer temperatures, you already know
that it has an effect on your
performance. How much? A study published in 2007 spells it out.
First
- you need to understand what "WBGT" is. WBGT stands for Wet Bulb Globe
Temperature and it is a method
of evaluating environmental
conditions that takes into account temperature, solar radiation (from
the sun), humidity and wind
speed. In other words it's a more
accurate representation of how hot it feels, rather than just
considering ONE of those factors
like temperature or humidity.
In their article "Impact
of Weather on Marathon Performance" published in the journal Medicine and Science in Sports and Exercise,
author
Matthew Ely and his co-authors
examine marathon performances across a spectrum from a WBGT of 5.1
degrees Celsius (about 41
degrees F) to 25 degrees C (77
degrees F). They broke the temperature into four range categories
(quartiles):
- 41 - 50 degrees F (5-10 degrees C)
- 50.1 - 59 degrees F (10.1 - 15 degrees C)
- 59.1 -
68 degrees F (15.1 - 20 degrees C)
- 68.1 - 77 degrees F (20.1
- 25 degrees C)
Marathon
results and weather data were
collected for several major
marathons including Boston, New York, Twin Cities, Richmond, Grandma's,
Hartford and Vancouver
over periods of 6-36 years. They
compared the top three finishers performances with course records for
the appropriate time
frame, and also compared
performances of "slower" marathoners (the 25th, 50th, 100th and 300th
place finishers)
with those course records. Both
males and females were studied.
Bottom line - WBGT does affect performance, and it's
not pretty. Two take aways:
- The higher the WBGT, the more
effect it has on performance
- The slower the runner, the bigger
the impact the WBGT has on performance.
The
authors devised a prediction formula that may be used to estimate how
much
performance suffers based on
temperature and race duration. Then they put the formula into a graphic
format (a nomogram).
Unfortunately they didn't evaluate
any times slower than the 3:00 finishers, but the trend is pretty clear;
environmental
conditions affect slower runners to a
greater degree than the faster ones, but even the elites at the front
are not immune
to the heat.
Consider these findings:
- The top 3 runners experienced only about .9% slower performance for each
5 degree C increase in WBGT.
- The 25th place finishers
saw a 1.1% hit to their performance for each 5 degree C.
- The 50th, 100th and 300th place finishers experienced an even greater impact of 1.5%, 1.8%, and 3.2% respectively
for each 5 degrees C increase in WBGT.
To
put that into perspective, the top
runners (for example a 2:10 finisher) might see thier average pace per
mile slow by only
about 2.7 seconds per mile for each 5
degrees C increase in WBGT. This means their "ideal" of 2:10 in the
lowest
WBGT quartile slows to about a 2:14
finish in a WBGT of 77 degrees F (25C). On the other end of the
spectrum, the 300th place
runner (the 3:00 marathoner) could
anticipate slowing by about 13.2 seconds a mile for each 5 degrees C
increase in WBGT.
That means their "ideal" 3:00 finish
in the lowest WBGT quartile slows to a 3:23 in the highest WBGT
quartile.
Using
the nomogram the authors devised from their formulas, you can see that
at
a WBGT of 68 degrees F (20 C) a
runner who is able to do a 2:30 marathon (150 minutes) in 40F might
expect about a 4% slower
time (about 6 minutes slower
overall) in these warmer conditions. A 3-hour marathoner in that same
environment could expect
a 9% slower finish time (about 16
minutes) vs. the cooler (41F) marathon! To use the prediction nomogram
below, simply find
the line that represents the WBGT on
race day, and then slide your finger down the line until you get to the
vertical line
that represents your athlete's cool
weather (41F) finish time. Now read across to the left to determine what
% performance
decrement to expect based solely on
the difference in WBGT.
Although
they didn't project out to higher temperatures or slower
athletes - if you just assume that
the performance of the 4:00, 4:30 and 5:00 marathoners is at least as
impacted as it was
for the 3:00 marathoner, you can use
the same multiplier to come up with a reasonable estimate of
performance in various temperatures.
For example -
- 4:00
marathon = 240 minutes. WBGT on race
day is 68 degrees F (20 C). There's a
3.2% hit for each category level above 5C so multiply 3.2% by 3 (you're
three catgories
warmer) to get 9.6%. Then it's
simple math:
- 240 X 1.096 =
263 minutes
- 263 minutes equates to 4:23
As
a coach - what do you do with this information? Use this information to
consider
how you schedule key races for your
athletes, and how you adjust your pace guidance on race day. Pacing
errors in a marathon
are all-too common; if your athlete
goes out too fast without respecting the hot and humid conditions, he or
she risks a disappointing
finish time and a pretty miserable
running experience.
Let's say your athlete has previously turned
in a 3:00 marathon
in cool temperatures (40 degrees F).
Today's race day dawns with a WBGT temperature of 60 degrees F (15 C).
Based on this
research, it's reasonable to
anticipate they'll be about 6% slower than they would be at around 40F.
If you do the math for
your 3:00 marathoner, you'll find it
changes the anticipated finish time to about a 3:10. Pace per mile
should be adjusted
from the "planned" 6:52 to a more
realistic 7:17. Failure to take the environmental conditions into
account will
likely come with a penalty later in
the race!
Although not a perfect substitute for WBGT, you can use heat index as
a starting reference. The National Weather Service heat index calculator can be found HERE and further explanation of WBGT can be found HERE
Medicine & Science in Sports & Exercise: March 2007 - Volume 39 - Issue 3 - pp 487-493.
About the author: Janet Hamilton is the author of the book "Running Strong & Injury-Free" (http://www.runningstrong.com/publicat.html) and she coaches runners & walkers through her business Running Strong (http://www.runningstrong.com). She has a master's Degree in Exercise Physiology and is a Registered Clinical Exercise Physiologist through the American College of Sports Medicine and a Certified Strength & Conditioning Specialist through the National Strength and Conditioning Association
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