Exercise Induced Bronchoconstriction, Part 1

Exercise or physical activity provides a number of benefits to health, mobility and quality of life. In 2007, the American College of Sports Medicine and the Centers for Disease Control and Prevention updated the national guidelines on Physical Activity and Public Health. They called for “moderate-intensity aerobic (endurance) physical activity for a minimum of 30 minutes on five days each week or vigorous-intensity aerobic physical activity for a minimum of 20 minutes on three days each week” together with activities to increase “muscular strength and endurance a minimum of two days a week”.1

However, exercise can cause sudden, acute narrowing of the airways, resulting in respiratory symptoms that include dyspnea, wheeze, and chest tightness in individuals who do, or do not have, pulmonary obstruction. These symptoms of bronchoconstriction are commonly associated with asthma. In individuals who have a diagnosis of asthma, and where the bronchoconstriction is triggered by exercise, it is referred to as Exercise Induced Asthma (EIA). 

The diagnosis of EIA is inaccurate for those individuals who have the symptoms brought on by exercise, but who do not have asthma, for it implies that they do have asthma. Hence, a distinction must be made. In its Clinical Practice Guidelines, The American Thoracic Society recommends the use of the term ‘Exercise Induced Bronchoconstriction’ (EIB) in all cases, to emphasize that not all bronchoconstriction is related to asthma.2

Some Benefits of Exercise

The Clinical Practice Guidelines on Physical Activity noted a dose-response relationship between physical fitness and health, and that regular exercise significantly decreases the risk of chronic disease, disability, weight gain, obesity and premature mortality. Diseases associated with inactivity include anxiety, cardiovascular disease, colon cancer, breast cancer, depression, hypertension, obesity, osteoporosis, thromboembolic stroke and type 2 diabetes mellitus.

Exercise, then, is essential for good health and for the maintenance of cognition and neural plasticity.3,4 Exercise has also been shown to reduce the risk of dementia and Alzheimer’s disease.5 Regular physical activity provides a sense of well-being; helps reduce stress, anxiety and depression; and increases flexibility, strength, agility and balance.6, 7

Symptoms of EIB

The symptoms of EIB – the result of sudden, transient narrowing of the airways – include some or all of the following: dyspnea, chest tightness, cough, wheezing, excess mucus, air hunger and increased effort required for breathing.8 Cough and chest tightness are the most common symptoms, but there may be many more subtle symptoms. Non-specific symptoms may include chest pain, prolonged respiratory illness, poor performance, avoidance of activity, inability to keep up with peers, and difficulty sleeping due to nocturnal symptoms. Abdominal pain, headache, muscle cramps, fatigue and dizziness may also result.

In individuals with asthma, the symptoms of bronchoconstriction appear after about 5 to 8 minutes of strenuous exercise. The bronchoconstriction plateaus for about two minutes and increases with more exercise. If the exercise ceases after fifteen minutes, the moderate bronchoconstriction will resolve spontaneously. If the individuals continue to exercise, they enter a refractory period that may last minutes or hours. This may be followed by an increase in symptoms. This is the late phase response, and the risk of its occurring is directly correlated to the severity of the initial response.9, 10

In EIB, exercise may be such a potent trigger that individuals with asthma will avoid exercising. This can have negative and detrimental consequences to their health. 

Many factors influence EIB. These include weather conditions, personal fitness, physical effort, air quality (including temperature, humidity, etc.), ventilation, duration of symptoms and both level of severity and degree of control of the asthma. 

Prevalence of EIB

EIB occurs in about 10% to 15% of the general population. However, athletes show a higher prevalence particularly in cold weather events and in ice-related athletic events where prevalence may range from 21% to 50%. EIB is also frequently reported in professional athletes and in individuals who are recreationally active.11 While persons with asthma tend to have more EIB (with an 80% to 90% prevalence), the level of EIB in individuals without a diagnosis of asthma can be as high as 20%.2 In increasing percentages, beginning with 12% in the general population, the percentage increases to 45% in individuals with allergic rhinitis and reaches an astonishing 50% for Olympic athletes.12

Studying this occurrence, Shaaban and colleagues13 analysed questionnaire data from 5158 individuals regarding physical activity, frequency and duration that resulted in symptoms such as breathlessness or sweating. Using a definition of bronchial hyperresponsivenes (BHR) as a post-saline decrease in Forced Expiratory Volume in one second (FEV1) of at least 20% for a maximum methacholine dose of 2 mg, they found some intriguing direct correlations. BHR was more prevalent in individuals with low education, obesity, atopy, asthma or asthma-like symptoms, in women who smoked (but not men); and in persons with lower FEV1.

The frequency and duration of physical activity was inversely correlated with BHR, with prevalence decreasing with the frequency of exercise and also with increasing duration of exercise. See Tables 1 and 2.

Exercise and BHR Prevalence
Frequency per week Prevalence of BHR Odds Ratio
< / = 1 per wk 14.5% 1.00
2 - 3 per wk 11.6% 0.78
= / > 4 per wk 10.9% 0.69

Table 1: Prevalence of BHR with exercise            

Exercise and BHR Prevalence
Frequency per week Prevalence of BHR Odds Ratio
< 1 per wk 15.9% 1.00
1 - 3 per wk 10.9% 0.70
= / > 4 per wk 10.7% 0.67

Table 2: Frequency of reported BHR with exercise


The precursor to asthma is bronchial hyperresponsiveness (BHR). There are two theories about the link between BHR and intense exercise. The first is that heat loss causes vasoconstriction as the airway cools. Re-warming of the airways causes vascular distention and edema from serum exudation into the interstitial fluid, and the release of mediators, leading to narrowing of the airways. The second theory proposes that initial water loss or dehydration in the airways results in activation of the epithelium and mast cells, releasing mediators that initiate the inflammatory cascade and end with epithelial injury. In both theories the end result is bronchoconstriction.14-16 The repair and regeneration process may lead to airway hyperresponsiveness in individuals without asthma.

There is an inflammatory basis to EIB.17, 18 Proinflammatory mediators from mast cells and eosinophils that are on and below the surface of the airways are involved in EIB for all individuals (both with and without asthma). These mediators change the osmolarity of the airway surface. Increased levels of mediators such as prostaglandins, histamines and leukotrienes, Tlymphocytes, macrophages, eosinophils and neutrophils have been found after exercise in children and adults with asthma, and in athletes who have EIB.16, 17

Exacerbations due to exercise may result in epithelial injury as a result of dehydration of the surface of the airway. Injury to the epithelium may lead to airway remodelling and also have an immediate two-fold effect: that of a reduction in the production of the bronchodilator prostaglandin E2, and plasma exudation which increases BHR to stimuli.

Diagnosis of EIB 

EIB is defined as short-lived, reversible bronchoconstriction that results from exercise. Since many other diseases mimic the symptoms, the diagnosis is not made on the basis of symptoms, but from an assessment of lung function. Serial lung function measurements after a specific exercise or challenge, as well as eucapnic voluntary hyperpnea or inhaled mannitol, are used to determine and assess the severity of EIB. FEV1 can also be taken before exercise and 30 minutes after. A drop  of >10% is used to diagnose EIB.

EIB severity is rated as mild, moderate or severe, depending on the post-exercise drop in FEV1. However, for an individual who is taking inhaled steroids, a percentage drop in FEV1 of >30% should cause the EIB to be rated as severe.2

Rating of severity of EIB
Mild > 10% to < 25%
Moderate > 25% to < 50%
Severe > 50%

Table 3: Rating of EIB using percentage drop in FEV1


A survey13 of asthma patients done between October 2009 and February 2010 showed that the diagnosis of EIB is often overlooked. The more symptoms an individual has, however, the more likely is the diagnosis of EIB. The survey defined the symptoms as cough, wheeze, shortness of breath, noisy breathing, chest tightness and trouble taking a deep breath after physical exertion or exercise. Table 4 lists the number of patients diagnosed with EIB according to the number of exercise-induced symptoms.

Number of symptoms Diagnosed with EIB
None 9%
One 12%
Two 19%
Three 18%
Four 27%
Five 32%
All six 30%

Table 4:    EIB diagnosed on the basis of symptoms

Continued in part 2.


BHR: Bronchial hyperresponsiveness
EIA: Exercise Induced Asthma
EIB: Exercise Induced Bronchoconstriction
EV1:Forced Expiratory Volume in one second


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