Does exercising in the heat increase muscle fatigue? There’s little doubt that working out in hot temperatures puts more stress on the body, and one of the consequences of this stress is quicker muscle fatigue. When you’re exercising in very warm temperatures, you may not be able to exercise as long before your brain sends a signal telling your muscles to slow down or stop. What causes muscles to fatigue more quickly when you exercise in the heat?
Exercising in the heat reduces blood flow to the brain as more blood is diverted to the skin to help release heat. This reduction in blood flow alters brain activity in such a way that “neuromuscular drive” is reduced, and brain input that tells the muscles to keep moving slows down. This is the brain’s way of protecting the body from overheating.
Another theory as to why muscles fatigue faster when you work out in the heat is free radical production. You’ve probably already heard about free radicals, those rogue molecules with unpaired electrons that do damage to cells and tissues. According to a study published in the American Journal of Physiology, exercising boosts the production of free radicals that can damage muscle proteins involved in muscle contraction. This leads to faster muscle fatigue. If you boost your levels of antioxidants before exercising in hot weather, will it help? No one knows for sure, but it’s certainly plausible.
Working out in hot weather may also contribute to hypoglycemia or low blood sugar level. This drop in blood sugar would speed up the breakdown of muscle glycogen stores and increase lactate production, which may contribute to muscle fatigue. This theory remains unproven at this point.
Reducing Muscle Fatigue When Exercising in the Heat
One of the most important things you can do to reduce muscle fatigue with exercise and reduce the risk of heat-related illness is to stay well hydrated. Even mild dehydration reduces blood flow to the brain and muscles and interferes with exercise performance.
Drink at least 3 glasses of fluid 2 to 3 hours before exercising in the heat. While working out, drink another cup of fluid every 15 minutes for the full duration of your exercise. If you’ll be exercising at a higher intensity or for more than one hour, sip a sports drink instead of water to replace electrolytes lost through sweating.
Consuming enough carbohydrates before exercising in heat helps to prevent hypoglycemia, which may contribute to earlier muscle fatigue. Most experts recommend consuming an easily-digestible carbohydrate 2 to 3 hours before exercise to optimize glycogen stores and blood sugar levels.
Dress in loose cotton clothing when exercising in hot weather to allow better airflow – and know the symptoms of heat-related illness. If you experience dizziness, lightheadedness, nausea or headache, stop exercising immediately and seek medical attention if the symptoms don’t improve within 30 minutes.
The Bottom Line?
Muscles fatigue faster when you exercise in the heat. Make sure you’re prepared by being well-hydrated and well-fueled with carbohydrates. If you exercise in the heat, do it safely.
References:
American Journal of Physiology. 279. C1058-66.
Exercise Physiology. Theory and Applications to Fitness and Performance. 2009.
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