Exercise-Induced Bronchoconstriction

The airways narrow because of what high-volume breathing does to the airway lining. During hard exercise, minute ventilation rises steeply and large volumes of air must be warmed and humidified quickly. Two overlapping mechanisms follow.

In the osmotic model, the rapid loss of water from the airway surface concentrates the fluid lining the airways, and this rise in osmolarity triggers mast cells to release inflammatory mediators such as histamine, leukotrienes and prostaglandins, which make the airway smooth muscle contract. In the thermal model, the airways cool during exercise and rewarm rapidly once it stops, producing vascular engorgement and narrowing of the airway wall.

This explains the pattern seen in sport. Cold, dry air demands more warming and humidifying and provokes more bronchoconstriction, which is why winter and endurance athletes are so often affected, while chlorine and pollutants add an inflammatory stimulus of their own. In elite athletes, years of sustained high ventilation may injure the airway lining and leave it more reactive, and allergy and rhinitis add to the picture.

The typical story is cough, wheeze, chest tightness and breathlessness that come on during exercise or, more often, in the ten to fifteen minutes after stopping, then settle within an hour. Some athletes notice a refractory period, where a second effort within a few hours provokes fewer symptoms. Performance may simply fall away without the athlete knowing why. Examination is usually normal at rest, so it is worth checking oxygen saturation, looking for nasal or allergic disease, listening to the chest and considering the heart.

Symptoms alone are a poor guide, since many athletes who report exertional breathing symptoms do not have EIB when tested, and some with EIB have few symptoms, so a history prompts investigation rather than settling the diagnosis. Consider what mimics EIB. Exercise-induced laryngeal obstruction (EILO), in which the larynx narrows at peak exercise, causes noisy breathing in and throat tightness that resolve quickly on stopping and do not respond to inhalers, in contrast to the expiratory wheeze of EIB that builds after exercise. Cardiac disease must be considered where there is chest pain, palpitations or fainting.

Because symptoms are unreliable, EIB is confirmed objectively wherever possible. Resting spirometry is a sensible start but is frequently normal, so it neither confirms nor excludes the condition. The diagnosis rests on a bronchoprovocation, or challenge, test that reproduces and measures the airway narrowing.

In an exercise challenge, forced expiratory volume in one second (FEV1) is measured before and repeatedly after a standardised bout of exercise, and a fall of at least ten per cent from the pre-challenge value is a positive test. Because a laboratory exercise test is hard to standardise, a surrogate that drives ventilation to similar levels is often used in athletes, the eucapnic voluntary hyperpnoea (EVH) test. Indirect inhaled challenges such as mannitol or hypertonic saline are further options, though these use their own thresholds, mannitol being positive with a fall of at least fifteen per cent from baseline.

A common cause of a falsely negative test is failure to withhold inhalers beforehand, so a short-acting beta-2 agonist is stopped for at least eight hours, a long-acting one for around forty-eight hours, and antihistamines before an osmotic challenge.

Objective testing matters even more in sport, since a confirmed diagnosis guides correct treatment, avoids medicating athletes who do not have EIB, and supports any anti-doping application. Where symptoms occur outside exercise, wake the athlete at night, vary with other triggers or come with abnormal baseline spirometry, coexisting asthma should be investigated on the current national pathway, which in adults begins with fractional exhaled nitric oxide or blood eosinophils. Persistent unexplained breathlessness with negative tests should raise EILO, confirmed by continuous laryngoscopy during exercise, along with dysfunctional breathing or a cardiac cause.

Management combines avoiding the trigger with treating the airway. Non-drug measures matter. An interval or variable-intensity warm-up before competition can induce a refractory period that reduces later bronchoconstriction, whereas a single hard effort may simply provoke symptoms. Reducing exposure to cold, dry air, for example with a heat-and-moisture-exchanging mask in winter sport, helps, as does attention to chlorine and air quality, and any allergic rhinitis or asthma is treated in its own right.

Drug treatment depends on whether asthma is present. For isolated EIB without asthma, an inhaled short-acting beta-2 agonist (SABA) such as salbutamol, taken ten to fifteen minutes before exercise, is an accepted first-line option, ideally needed less than daily. For EIB in someone with confirmed asthma, treatment follows the current national asthma pathway rather than a reliever alone, which for those aged twelve and over generally means an inhaled corticosteroid (ICS) combined with formoterol as anti-inflammatory reliever therapy, stepping up to regular maintenance if control is inadequate. Needing a reliever before every session is a warning sign that should prompt controller treatment and a review of the diagnosis. A leukotriene receptor antagonist such as montelukast is an option, though patients should be warned about neuropsychiatric effects such as sleep or mood disturbance and reviewed if these develop.

Anti-doping shapes prescribing. Beta-2 agonists appear on the World Anti-Doping Agency (WADA) Prohibited List, but several inhaled ones are permitted within set limits without a Therapeutic Use Exemption (TUE). Inhaled salbutamol is permitted up to a maximum of 1,600 micrograms over 24 hours, with no more than 600 micrograms over any 8 hours, and inhaled corticosteroids are permitted. Exceeding these limits, or using a prohibited beta-2 agonist such as terbutaline, requires a TUE, which objective evidence of EIB supports, while a TUE is not needed for permitted agents used within the thresholds. Because the limits change between annual lists, the current WADA list and Global Drug Reference Online should always be checked.

EIB should not hold an athlete back, and with warm-up, environmental measures and the right inhaled treatment athletes compete at the highest level. Review checks inhaler technique, which is often poor, adherence and how often reliever therapy is used, stepping up controller treatment when reliever use is frequent.

If significant symptoms develop during exercise the athlete should stop, use their reliever and resume only once symptoms settle, treating severe or non-resolving symptoms as a possible acute asthma attack, and athletes with asthma should hold a written personalised action plan with ready access to their reliever. Where an athlete is not improving despite reasonable treatment, the diagnosis deserves another look, since persistent symptoms may reflect EILO, dysfunctional breathing, uncontrolled asthma or a cardiac problem rather than undertreated EIB.

• •The current joint British Thoracic Society (BTS), National Institute for Health and Care Excellence and Scottish Intercollegiate Guidelines Network (SIGN) asthma guideline underpins the diagnosis and pharmacological management of coexisting asthma.
• •Respiratory society statements, including the American Thoracic Society (ATS) guideline on exercise-induced bronchoconstriction, set out the objective diagnostic criteria and the role of challenge testing.
• •UK Anti-Doping (UKAD) and WADA guidance define the permitted inhaled beta-2 agonist limits and when a Therapeutic Use Exemption is required.
• •Sport and exercise medicine consensus recognises the high prevalence of EIB in endurance and winter athletes and the importance of objective diagnosis.

• •Exercise-induced bronchoconstriction is transient airway narrowing during or after exercise, occurring with or without underlying asthma.
• •Distinguish EIB, an expiratory wheeze building after exercise, from exercise-induced laryngeal obstruction, an inspiratory noise at peak effort that does not respond to inhalers.
• •Symptoms correlate poorly with the diagnosis, which is confirmed by a fall in forced expiratory volume in one second of at least ten per cent after an exercise or eucapnic voluntary hyperpnoea challenge, with inhalers withheld beforehand.
• •For isolated EIB a short-acting beta-2 agonist before exercise is first-line, while EIB with asthma follows the national asthma pathway with an inhaled corticosteroid.
• •Inhaled salbutamol is permitted up to 1,600 micrograms over 24 hours, with no more than 600 micrograms over any 8 hours, and terbutaline needs a Therapeutic Use Exemption.
• •Check the current WADA list and Global Drug Reference Online, since inhaled limits change between annual lists.