Fatigue After Light Exertion

What Causes Fatigue After Slight Exertion?

Fatigue after slight exertion can have various causes, ranging in severity from 'minor' to 'generally fatal'.  Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.

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Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms.  In order to diagnose fatigue after slight exertion, we could:

  • Research the topic
  • Find a doctor with the time
  • Use a diagnostic computer system.
The process is the same, whichever method is used.

Step 1: List all Possible Causes

We begin by identifying the disease conditions which have "fatigue after slight exertion" as a symptom.  Here are eight of many possibilities (more below):
  • Gilbert's Syndrome
  • Anemia
  • Magnesium Need
  • Congestive Heart Failure
  • Arrhythmias
  • Valley Fever (Coccidioidomycosis)
  • Low Estrogens
  • Mercury Toxicity

Step 2: Build a Symptom Checklist

We then identify all possible symptoms and risk factors of each possible cause, and check the ones that apply:
constant fatigue
diuretic use
history of birth control pill use
chronic mild mouth soreness/sores
being very skinny
multiple swollen inguinal nodes
major joint pain/swelling/stiffness
heart racing/palpitations
recent breastfeeding
very low hemoglobin levels
loss of appetite
painful inguinal nodes
... and more than 100 others

Step 3: Rule Out or Confirm each Possible Cause

A differential diagnosis of your symptoms and risk factors finds the likely cause of fatigue after slight exertion:
Cause Probability Status
Gilbert's Syndrome 93% Confirm
Anemia 27% Unlikely
Arrhythmias 18% Unlikely
Magnesium Need 1% Ruled out
Valley Fever (Coccidioidomycosis) 0% Ruled out
Low Estrogens 0% Ruled out
Mercury Toxicity 0% Ruled out
Congestive Heart Failure 0% Ruled out
* This is a simple example to illustrate the process

Arriving at a Correct Diagnosis

The Analyst™ is our online diagnosis tool that learns all about you through a straightforward process of multi-level questioning, providing diagnosis at the end.

If you indicate being fatigued, The Analyst™ will ask further questions including this one:
Do you get tired easily, even with slight physical exertion?
Possible responses:
→ Don't know
→ No
→ Occasionally / moderately
→ Severely - almost any kind of activity tires me
Based on your response to this question, which may indicate no fatigue after slight exertion, fatigue after slight exertion or severe fatigue after slight exertion, The Analyst™ will consider possibilities such as:
Andropause/Male Menopause

Lethargy and lack of vitality are early signs that your anti-aging hormones (such as testosterone) are diminishing.


An inefficient pumping action by the heart can result in rapid fatigue.

Estrogens Low

Lethargy and lack of vitality are early signs that your anti-aging hormones (such as estrogen and progesterone) are diminishing.

Lupus, SLE (Systemic Lupus Erythematosus)

90% of patients with SLE experience fatigue.

Magnesium Requirement

Early symptoms of magnesium deficiency can include fatigue.

Multiple Sclerosis

Demyelinated nerve fibers use more energy to conduct impulses and thus fatigue more easily than normal fibers.  MS involves large numbers of nerve fibers in a state of borderline function, which suddenly turn off when the body temperature is elevated only one or two degrees.  The signals suddenly cease to be transmitted, and one has to stop.  Muscles that have been weakened result in a reliance on stronger muscles, which then tire faster.  One recent report indicates that for those with MS the energy cost of walking is two to three times that of a normal person over the same distance.  Such an increased use of energy obviously results in increased fatigue.  The fatigue of MS is hard to describe.

... and also rule out issues such as:
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