Thursday, September 1, 2011

DrMirkin's eZine: Hot-weather exercise, longevity, more . . .

Dr. Gabe Mirkin's Fitness and Health E-Zine
September 4, 2011

Exercising in Hot Weather

With each increase in environmental temperature from 62
to 89 degrees Fahrenheit, cyclists have higher body temperatures,
lose more power and ride slower (International Journal of Sports
Physiology and Performance, June, 2011).
The loss of power precedes a marked rise in body temperature
(Journal of Sports Science, January 2010). Muscles are made up
of millions of individual nerve fibers. You contract only a few,
never all, muscle fibers at the same time. The greater the
percentage of fibers you contract at the same time, the greater
the force generated and the faster you can go. When you exercise
in hot weather, you lose power, speed and endurance before your
body temperature rises because you contract fewer fibers at the
same time (Pflugers Archiv, July 2004).
MECHANISM: The limiting factor in how fast and long you
can exercise is the time it takes to bring oxygen into muscles.
When you can't keep up with your needs for oxygen, you slow
down. More than 70 percent of the energy supplied to power your
muscles is lost as heat. The faster you go, the more heat your
muscles produce. A rise in muscle temperature makes your muscles
require even more oxygen, so it slows you down.
Your heart pumps oxygen-rich blood to your muscles.
As your temperature rises, your heart has to work harder to pump
the hot blood from your muscles to your skin to dissipate the
heat. This extra blood pumped to your skin reduces the amount of
oxygen-rich blood available to be pumped to your muscles, so you
have to slow down.
Cyclists who take sugar during races do not slow down as early
as those who take placebos (Journal of Applied Physiology,
April, 2008), and they are able to exercise longer
(International Journal of Sport Nutrition and Exercise
Metabolism,. April 2004). Taking sugared drinks during races
helps you ride faster at any environmental temperature, but in
hot weather, it helps you maintain your power and speed even
more. Since sugar requires less oxygen to power your muscles
than fat and protein do, taking extra sugar reduces oxygen needs
and allows you to ride faster.
took cold drinks (4 degrees C) every ten minutes had slightly
lower body temperatures, and rode faster and longer than those
who took their drinks at warmer temperatures (Journal of Sports
Science, September 2010). A review of ten studies on the
subject showed that cold drinks lower body temperature and can
improve performance by as much as 10 percent (International
Journal of Sport Nutrition and Exercise Metabolism, April 2010).
ACCLIMATIZATION: If you want to race at your best in
hot weather, you have to train in the heat and live in the heat.
You can't just go from a cold climate to a hot one and expect to
be able to tolerate the heat or race effectively. Acclimatization
to hot weather exercise can be accomplished only by exercising
intensely in the heat, not just by living in hot weather.
It takes at least a couple of weeks of exercising intensely in
the heat to acclimatize. The more fit you are, the better you
can tolerate the heat.
CAUTION: Exercising in the heat increases your risk for
heat stroke and heat exhaustion. See
FOR THE COMPETITIVE ATHLETE: Pre-cooling helps you to
ride faster in the heat. If you lower your temperature and
drink cooled fluids before you start to race, you can ride
faster at the start and during that race. The most effective
way to do this is to: *take a sugared and iced drink before the
race (J Sports Sci. 2007) and *immerse the racer up to his neck
in cold water (Med Sci Sports Exerc, 1997;29(7). The fastest
time trials were accomplished by cyclists who preceded their
time trials by taking large volumes of a sugar-ice drink (up to
one liter ) and by plunging their bodies into cold water for ten
minutes (Med Sci Sports Exerc, Jan, 2011). However I can find
no studies on the safety of pre-cooling. I know that people
with blocked arteries leading to their hearts could suffer
irregular heartbeats and even heart attacks.


Reports from

Rest periods between intervals

Omega-3's from plants



Dear Dr. Mirkin: Do your genes determine how long you live?

Genes appear to be more important in determining who will
live beyond 100, but in people who live into their nineties, how
sick you become and how long you live are determined more by
what you do than by your genes.
WHO IS LESS LIKELY TO DIE? Middle-aged people are 63
percent less likely to die within 18 years if they avoid
smoking, eat a low-fat and low-sugar diet, exercise regularly,
and drink alcohol moderately (American Journal of Public Health,
published online August 18, 2011). Compared to those who
followed none of these healthful living habits, those who
followed all four were protected for:
*11.1 years from all-causes of death,
*14.4 years from malignant cancers,
*9.9 years from heart attacks, and
*10.6 years from other causes of death.
Smoking was the strongest risk factor for premature death
people who never smoked, were not overweight, exercised at least
3.5 hours per week, and ate a healthful diet had an 80 percent
decreased risk of chronic diseases. After being followed for
almost eight years, they had:
*93 percent lower risk of diabetes,
*81 percent lower risk of heart attacks,
*50 percent lower risk of strokes, and
*36 percent lower risk of cancers
If you added in taking no more than two drinks a day, the
benefits would have been even greater. Being overweight was
the strongest risk factor for serious disease. Next came
smoking, followed by lack of exercise, and then by a high fat
and sugar diet (Archives of Internal Medicine, August 10/24,


Dear Dr. Mirkin: Can taking calcium supplements cause heart

PILLS. Many studies show that taking more than 500 mg/day of
calcium pills is associated with an increased risk for heart
attacks (Endocrine Practice, published online August 19, 2011).
Therefore most medical organizations recommend that you never
take more than 1200 mg/day of calcium from pills plus food
(Journal of Bone and Mineral Research, April 2011).
NMOL/L. Since vitamin D markedly increases the absorption of
calcium, you probably should never take vitamin D pills that
raise blood levels of vitamin D3 beyond 50 ng/mL (125 nmol/L).
A review of the world's literature shows that the upper safe
level of intake for vitamin D is between 4,000 and 10,000
IU/day and for calcium, from food and pills, between
2,000 - 3,000 mg/day.


Recipe of the Week:

Sweet Potato Bisque

You'll find lots of recipes and helpful tips in
The Good Food Book


"Like" us on Facebook



BACK ISSUES of the eZine from 2004-2011 are available at

YOU ARE WELCOME TO COPY the e-Zine's contents for
use in your own newsletter, company or club publication,
BLOG or website. Please give proper credit and a link
back to

The e-Zine is provided as a service. Dr.Mirkin's reports and
opinions are for information only, and are not intended to
diagnose or prescribe. For your specific diagnosis and
treatment, consult your doctor or health care provider.
For more information visit

We DO NOT sell, rent or give your e-mail address to anyone.
Copyright 2011 The Sportsmedicine Institute, Inc.

Gabe Mirkin, M.D.
10901 Connecticut Avenue, Kensington MD 20895, USA

To unsubscribe or change subscriber options visit:


Post a Comment