My Pet is Tired: Exercise Intolerance or Lethargy?

Change in behavior is a common sign that something is wrong with your pet. Dogs have numerous coping and defense mechanisms, with lethargy and exercise intolerance both signaling different diseases. Here, the difference between lethargy and exercise intolerance will be discussed, as well as what to do if your dog is displaying changes in behavior.

Lethargy vs. Exercise Intolerance

Lethargy and exercise intolerance can be difficult to distinguish because they both are characterized by inactivity. The hallmarks of a lethargic dog are unusual drowsiness, more time spent sleeping than normal, and reduced energy.

Exercise intolerance, while similar, has different symptoms. A dog suffering from exercise intolerance will show decreased endurance or speed during exercise. An exercise intolerant dog may also show symptoms of coughing, gagging, fainting, or collapse, but only during activity.  

Sometimes, a dog will show symptoms of both lethargy and exercise intolerance. Indeed, these symptoms can overlap for certain diseases. However, understanding what your dog is experiencing is the first step to diagnosing and treating your pet.

Causes of Lethargy in Dogs

The main causes of lethargy in dogs include:

  • Anemia
  • Arthritis
  • Cancer
  • Diabetes
  • Fever
  • Heart disease
  • Infectious disease
  • Malnutrition
  • Obesity
  • Pain
  • Parasites
  • Pneumonia
  • Thyroid disorders
  • Tick-borne illness

Causes of Exercise Intolerance in Dogs

The main causes of exercise intolerance in dogs include:

  • Anemia
  • Chemotherapy
  • Collapsed trachea
  • Heart disease
  • Infectious disease
  • Kidney disease
  • Laryngeal paralysis
  • Lung disease
  • Neuromuscular disease
  • Obesity
  • Parasites
  • Parasites
  • Thyroid disease
  • Upper respiratory disease

What to do if you Suspect Exercise Intolerance or Lethargy

If you suspect your dog is showing signs of either exercise intolerance or lethargy (or both), the first step is to make an appointment with your veterinarian. Many of the diseases listed here are treatable when caught in time. Depending on your dog’s other symptoms, your veterinarian will perform a physical exam and may order laboratory testing. If a heart or lung condition is suspected, x-ray or an echocardiogram may be performed as well.

Ultimately, early detection is key. Lethargy can be difficult to identify, particularly for pet owners who are away from home during the day. The Actijoy dog activity tracker will alert you when your dog is less active than normal. This feature allows pet owners to identify and make note of problems the moment they appear, providing the best chance for recovery. 


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Please note: all dogs should be treated as individuals. The Actijoy™ blog is for educational and entertainment purposes only. In the case of emergency, always seek qualified healthcare from a local veterinarian or emergency facility. Actijoy™ blogs are not designed to treat, diagnose, or prescribe medication for your pet.

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