Exercise-induced asthma, more precisely called exercise-induced bronchoconstriction (EIB), is diagnosed by measuring how much your lung function drops after a bout of intense exercise or a breathing challenge. Symptoms alone aren’t enough. The American Thoracic Society is clear on this point: the diagnosis requires an objective, measurable decline in airflow, not just a history of coughing or wheezing during workouts.
Baseline Spirometry Comes First
Before any challenge test, you’ll do a baseline spirometry reading. You breathe out as hard and fast as you can into a mouthpiece, and the machine records two key numbers: how much air you can force out in one second (FEV1) and the total volume of that forced breath (FVC). The ratio between these two numbers tells your doctor whether your airways are already narrowed at rest. A ratio below about 75% of what’s expected for your age, height, and sex suggests airflow obstruction that may point to underlying asthma.
This baseline number also serves as your “before” measurement. Everything that follows compares post-exercise lung function to this starting point.
The Exercise Challenge Test
The most straightforward way to test for EIB is to exercise in a controlled setting and then measure what happens to your airways. You’ll typically run on a treadmill. The protocol starts at a low speed, ramps up over about two to three minutes, and then holds you at a heart rate between 80% and 90% of your predicted maximum (calculated as 220 minus your age) for four minutes. The whole exercise portion takes roughly six to eight minutes.
As soon as you stop, the real test begins. You’ll blow into the spirometer at set intervals: 5, 10, 15, and 30 minutes after exercise. Each reading is compared to your baseline. A drop in FEV1 of 10% or more is the standard threshold for a positive diagnosis. Many labs use a stricter cutoff of 15% because it reduces the chance of a false positive. Some recent research suggests 13.5% may be the most accurate dividing line.
Severity follows a simple scale. A 10% to 25% drop is classified as mild, 25% to 50% as moderate, and anything above 50% as severe. Most people with EIB fall into the mild category.
One important quirk: a single negative exercise challenge doesn’t fully rule out EIB. The airway response can vary from day to day depending on conditions like temperature, humidity, and allergen exposure. Guidelines recommend two negative tests before confidently excluding the diagnosis.
Breathing Challenges Without Running
Exercise isn’t the only way to provoke the airway narrowing. In fact, for competitive athletes, it’s not even the preferred method. Two alternatives are widely used.
Eucapnic Voluntary Hyperpnea (EVH)
This test skips the treadmill entirely. Instead, you breathe rapidly from a tank containing a dry gas mixture (21% oxygen, 5% carbon dioxide, the rest nitrogen) for six minutes, aiming to sustain about 85% of your maximum breathing capacity. The dry air and high ventilation rate mimic what happens in your lungs during hard exercise, but more intensely and more consistently than a treadmill can.
The International Olympic Committee endorses EVH as the preferred challenge for diagnosing EIB in athletes. It was originally developed in 1984 to screen military recruits and has been used in competitive sports for over 25 years. After the six-minute breathing period, spirometry is performed at the same intervals as an exercise challenge, and the same FEV1 drop thresholds apply. The biggest decline usually shows up between 5 and 10 minutes after the challenge ends.
Mannitol Inhalation Challenge
Mannitol is a sugar alcohol delivered as a dry powder through an inhaler in increasing doses. When it reaches your airways, it draws water out of the airway lining through osmosis. In people with EIB, this triggers the release of inflammatory chemicals from immune cells, causing the airways to tighten. In healthy people, nothing happens.
The mannitol test has a practical advantage: it doesn’t require a treadmill, a gas tank, or much specialized equipment. It’s also more reproducible than an exercise challenge. In comparative studies, it proved therapeutically equivalent to methacholine (another common airway challenge) for identifying EIB and diagnosing asthma, while being faster and more consistent.
Preparing for Your Test
What you take, eat, and do before the test matters. Many common asthma and allergy medications can suppress the airway response and produce a falsely normal result. Guidelines specify how long each type of medication should be stopped before a challenge:
- Short-acting rescue inhalers (like albuterol): 8 hours
- Long-acting bronchodilator inhalers: 36 hours
- Ultra-long-acting combination inhalers: 48 hours
- Standard inhaled corticosteroids: 6 hours
- Long-acting inhaled corticosteroids: 24 hours
- Leukotriene receptor antagonists (like montelukast): 4 days
- Antihistamines: 72 hours
Beyond medications, you should avoid caffeine on the day of the test, skip exercise that day entirely (prior exertion can temporarily protect your airways and mask the response), and be free of any respiratory infection for at least six weeks. Your doctor will walk you through the specific withholding schedule based on what you take.
What EIB Looks Like vs. Vocal Cord Dysfunction
Not every case of exercise-related breathing trouble is EIB. Vocal cord dysfunction (VCD) is a common mimic, and the two can even coexist. The timing of symptoms is the biggest clue. EIB symptoms typically peak 5 to 20 minutes after you stop exercising, while VCD causes breathing difficulty during exercise that resolves quickly once you stop.
On spirometry, the distinction shows up in the shape of the breathing curve. EIB affects the expiratory (breathing-out) portion. VCD flattens the inspiratory (breathing-in) portion, because the vocal cords are closing when they should be open. If your doctor suspects VCD, you may be referred for laryngoscopy, where a small camera is passed through the nose to watch the vocal cords in action. The classic finding is the front two-thirds of the cords squeezing together during inhalation, leaving only a small diamond-shaped gap at the back.
Another telling sign: people with VCD often maintain oxygen saturation above 97% even during significant respiratory distress, which would be unusual during a true asthma flare.
Monitoring at Home With a Peak Flow Meter
If you’ve been diagnosed with EIB and want to track your response to exercise day to day, a peak flow meter is a simple, portable tool. It measures how fast you can push air out in a quick, forceful breath. The number drops when your airways are narrowed.
Taking a reading before exercise and again afterward gives you an objective check on whether your airways are tightening. A significant drop in your peak flow number, especially paired with symptoms like coughing, chest tightness, or wheezing, signals that you may need your rescue inhaler or a break from activity. Over time, tracking these numbers helps you and your doctor fine-tune treatment and understand which conditions (cold air, high pollen counts, intense intervals) are your biggest triggers.