You love to
exercise outside in the fresh air, but certain times during the year are
downright hot and sticky. Harsh summer conditions may mean it’s challenging to
exercise outdoors.
Knowing how to handle
these outdoor conditions will protect you from fatigue and heat-related
diseases. Jason R. Karp, PhD, exercise physiologist and owner of
RunCoachJason.com, discusses what you can do to prepare yourself for the summer
heat.
Beginning a
workout fully hydrated or even “hyperhydrating” (hydrating to a greater degree
than normal) before a workout can delay dehydration during exercise, maintain
exercise performance and decrease the risk for heat-related illnesses.
Pre-exercise
fluid intake enhances your ability to control body temperature and increases
plasma volume to maintain cardiac output. You should drink enough fluids before
exercising in the heat to begin every workout fully hydrated, and you should
continue to drink during workouts longer than 1 hour. (See next section for
specific guidelines of what to drink.)
A good
indicator of your hydration levels is urine color. The lighter the urine color,
the better the level of hydration. Your urine should look like lemonade rather
than apple juice.
What Should You Drink?
FLUID
Before
Exercise. Drink 500 milliliters (ml) 2 hours before exercise.
During
Exercise. Drink about 200 ml every 15–20 minutes, aiming to match fluid intake to
sweat loss. Maintain 400–600 ml of fluid in the stomach to optimize gastric
emptying.
After
Exercise. Drink 1 liter (L) per kilogram (kg) of weight lost during exercise.
SODIUM
Sodium intake is necessary only if exercise lasts more than 60 minutes or if
you have a sodium deficiency. Before, during and after exercise, consume
0.5–0.7 gram (g) per L of fluid.
GLYCEROL
Drinks that contain glycerol cause fluid retention. This effect facilitates
hyperhydration, protects against dehydration and maintains core body
temperature.
Before
Exercise. Ingest 1.2 g per kg of body weight in a 20% glycerol solution within a
30-minute period, followed by 26 ml of water per kg of body weight, distributed
over the 90 minutes prior to exercise.
During
Exercise. Ingest 0.125 g per kg of body weight mixed in 5 ml of fluid per kg of body
weight.
After
Exercise. Ingest 1.0 g per kg of body weight mixed in 1.5 L of fluid.
Acclimatize
Chronically exposing yourself to a hot and humid environment simulates
adaptations that lesson the stress. Cardiovascular adaptations to exercising in
the heat are nearly complete within 3–6 days. Full acclimatization becomes
complete after 2 weeks as the increased sweating response catches up to the
other adaptations. Therefore, take 2 weeks of slowly introducing yourself to
the heat to be fully acclimatized and prepared for prolonged continuous
exercise.
SIDEBAR:
Recommendations for Heat Acclimatization
Sources
Armstrong, L.E. 2000. Performing
in Extreme Environments. Champaign, IL: Human Kinetics.
Casa, D.J. 1999. Exercise in the heat. II. Critical concepts in rehydration,
exertional heat illnesses, and maximizing athletic performance. Journal of
Athletic Training, 34 (3), 253–62.
Robergs, R.A., & Griffin, S.E. 1998. Glycerol: Biochemistry,
pharmacokinetics and clinical and practical applications. Sports Medicine,
26 (3), 145–67.
van Rosendal, S.P., et al. 2010. Guidelines for glycerol use in hyperhydration
and rehydration associated with exercise. Sports Medicine, 40 (2),
113–29.