Fever After Exercise: When to Worry
FitnessRecovery & Safety

How to Tell When a Fever After Excessive Exercise Is Too Serious to Ignore

How to Tell When a Fever After Excessive Exercise Is Too Serious to Ignore
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Updated on November 12, 2025
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Working your muscles during exercise generates heat. The more intense and prolonged the exercise, the more heat your muscles generate.

Your body primarily dissipates this heat by sweating. As the sweat evaporates, body heat is lost.

A slight increase in body temperature is not unusual during or immediately after exercise, especially in hot and humid environments.

However, a significant elevation in body temperature could signal exertional heat illness (EHI), a group of heat-related conditions ranging from mild cramps to heat exhaustion and heatstroke.

A high or persistent fever after exercise should not be ignored.

Types of Exertional Heat Illness 

EHI encompasses a group of heat-related conditions that can occur with intense exercise. These conditions range from minor to potentially life-threatening.

The level of increase in body temperature, along with other factors like hydration status and electrolyte balance, are key in determining the severity of EHI.

EHIs include:

  • Exercise-associated muscle cramping
  • Exertional heat exhaustion
  • Exertional heatstroke

Signs and Symptoms of Exertional Heat Illness

Muscle cramps can develop with intense exercise at any temperature but occur more frequently in a hot environment. Muscle cramps may be the first sign of overheating. If you’re experiencing muscle cramps, it’s important to rest and hydrate.

Continued exercise with an elevated body temperature could lead to heat exhaustion, which requires quick treatment to cool and rehydrate the body. Common symptoms of heat exhaustion include:

  • Dizziness
  • Muscle cramps
  • Lightheadedness or fainting
  • Nausea, diarrhea, or abdominal cramps
  • Weakness and reduced performance
  • Profuse sweating or cool, clammy skin
  • Hyperventilation
  • Fast heart rate
  • Headache

Exertional heatstroke is life-threatening and requires emergency medical attention. Body temperature is an important factor in differentiating exertional heat exhaustion from heatstroke.

A temperature of 104.9 degrees F or higher typically indicates exertional heatstroke. A body temperature of 101 to 104 degrees F suggests exertional heat exhaustion. However, the capacity to tolerate elevated body temperature varies, so accompanying signs and symptoms are also important.

In addition to a body temperature of 104.9 degrees F or higher, symptoms of heatstroke may include:

  • Disorientation
  • Confusion
  • Irritability
  • Aggressiveness or irrational behavior
  • Staggering or collapsing
  • Hot skin that may be wet or dry
  • Vomiting or diarrhea
  • Fainting
  • Seizures or coma

Environmental Factors

EHI is most likely to occur in hot, humid conditions. This type of environment limits the effectiveness of cooling your body through sweating.

Intense sweating in a hot environment also causes you to lose more of your body’s water, which further compromises your body’s ability to maintain a normal temperature.

Although less common, EHI can also occur with prolonged or intense exercise in cool environments, especially if your clothing or protective equipment limits your body’s ability to cool itself.

Warnings and Considerations

An elevated body temperature after working out is usually related to overexertion. It typically returns to normal within an hour or two with rest and hydration.

Keep in mind that a fever sometimes occurs coincidentally after intense exercise. It may be a symptom of a cold, the flu, or a stomach virus.

A persistent or delayed fever after intense or prolonged exercise might indicate another problem.

For example, extreme exercise when you’re not accustomed to it may lead to muscle tissue breakdown. Known as exertional rhabdomyolysis, this condition is characterized by widespread muscle soreness, tenderness, and weakness.

Rhabdomyolysis also causes a fever and brown urine due to muscle proteins leaking into the bloodstream. Immediate medical attention is needed to prevent serious complications, such as kidney failure.

The Takeaway

  • A slight increase in body temperature is not unusual during or immediately after exercise, especially in hot and humid environments.
  • Resting and hydrating can help your body cool down and return to a normal body temperature.
  • A high fever that doesn’t resolve quickly after prolonged exercise can be a sign of exertional heat exhaustion or exertional heatstroke. Heatstroke is an emergency and requires immediate medical attention.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Griffin L et al. A Review of Exertional Heat Illnesses. American Orthopaedic Society of Sports Medicine. 2024.
  2. O’Connor F et al. Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis. UpToDate. August 6, 2025.
  3. Heat Exhaustion. Cleveland Clinic. October 1, 2024.
  4. Rhabdomyolysis. MedlinePlus. August 28, 2023.
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Justin Laube

Justin Laube, MD

Medical Reviewer

Justin Laube, MD, is a board-certified integrative and internal medicine physician, a teacher, and a consultant with extensive expertise in integrative health, medical education, and trauma healing.

He graduated with a bachelor's in biology from the University of Wisconsin and a medical degree from the University of Minnesota Medical School. During medical school, he completed a graduate certificate in integrative therapies and healing practices through the Earl E. Bakken Center for Spirituality & Healing. He completed his three-year residency training in internal medicine at the University of California in Los Angeles on the primary care track and a two-year fellowship in integrative East-West primary care at the UCLA Health Center for East-West Medicine.

He is currently taking a multiyear personal and professional sabbatical to explore the relationship between childhood trauma, disease, and the processes of healing. He is developing a clinical practice for patients with complex trauma, as well as for others going through significant life transitions. He is working on a book distilling the insights from his sabbatical, teaching, and leading retreats on trauma, integrative health, mindfulness, and well-being for health professionals, students, and the community.

Previously, Dr. Laube was an assistant clinical professor at the UCLA Health Center for East-West Medicine and the David Geffen School of Medicine at UCLA, where he provided primary care and integrative East-West medical consultations. As part of the faculty, he completed a medical education fellowship and received a certificate in innovation in curriculum design and evaluation. He was the fellowship director at the Center for East-West Medicine and led courses for physician fellows, residents, and medical students.

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Christine St. Laurent, PhD, MPH

Author

Christine W. St. Laurent, PhD, MPH, is a scholar-practitioner who studies the interactions between physical activity, sedentary behavior, and sleep and their impact on physical, social-emotional, and cognitive development in children.

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