Exercise as it relates to Disease/Aerobic Training and Exercise-Induced Asthma

Asthma is a chronic respiratory condition which causes a temporary narrowing and constricting of the airways. This airway inflammation is a result of mucus production, muscle tightening, and swollen bronchial membranes in the airways. Factors which induce asthmatic symptoms in patients, called triggers, vary between individuals as does the severity of the condition.

Exercise-induced asthma (EIA) occurs when asthma symptoms are stimulated by vigorous exercise. Exercise itself does not cause asthma, however it is quite often a trigger, and affects about 90% of regular asthma sufferers. Most often this activity is aerobic in nature, with certain sports such as long distance running, cycling and cross-country skiing more likely to cause worsened symptoms than others.

Spirometry is used to diagnose exercise-induced asthma, and is present when there is a reduction in forced expiratory volume or peak expiratory flow following aerobic activity. As of 2011, approximately 1 in 10 (over 2 million total) Australians suffer from Asthma.

Effect on Exercise Participation
Whilst it is generally recommended that asthma sufferers avoid potential triggers, having exercise-induced asthma should not stop someone from enjoying the benefits of exercise, or from reaching their exercise goals.

Symptoms

 * Generally start 5–20 minutes after beginning exercise, and peak 5–10 minutes after stopping exercise
 * Coughing and wheezing
 * Excessive phlegm
 * Chest pain
 * Prolonged shortness of breath
 * Elevated and irregular respiratory rate
 * Extreme fatigue

How Aerobic Activity Induces Asthma Symptoms
When at rest, breathing through the nose serves to warm and humidify air before it travels through the airways to the lungs. The increased demand for oxygen when exercising results in a switch from breathing through the nose to the mouth. The air from this passageway is therefore a lot colder and drier because it has not been warmed and humidified in the nasal passage. This contrast in the air temperature can lead to asthmatic symptoms due to the increased risk and sensitivity of the bronchial smooth muscle lining the airways to inflammation and contraction.

Refractory Period
If symptoms of asthma or of an asthmatic attack occur as a result of exercise, it is often followed by a period of time where the lungs and airways are less likely to respond as strongly. This is referred to as the refractory period, and can last for anywhere up to two hours after the beginning of physical activity. Some exercise-induced asthma sufferers will know their condition well enough that they can use the refractory period as a loophole for participating in aerobic activity without symptoms.

How to Control Exercise-Induced Asthma
Treatment of exercise induced asthma with regards to aerobic training should aim to minimise the risk and prevalence of an asthma attack. Medication is often prescribed depending on the severity of the asthma. Bronchodilators used during or before exercise to assist in keeping the airways relaxed and open, or anti-inflammatory medication to reduce the sensitivity of the airways, are commonly used to prevent symptoms during aerobic training. Elite athletes need to ensure the legality of the medication they are taking within their National Federation Anti-Doping Agency, as a large portion of pharmaceutical prescriptions can be found on the banned substance list.

Management During Exercise
Suggested management techniques for participating aerobic activities:

Exercise Recommendations
As well as the obvious health benefits of regular aerobic exercise, physical activity is generally considered beneficial for those with asthma;
 * Regular aerobic training increases muscular strength and cardiopulmonary endurance, therefore reducing the ventilation rate required for specific tasks. This reduces the strain on the cardiorespiratory system during exercise and decreases the risk of an asthma attack for low intensity exercise.
 * Good cardiovascular fitness will allow exercise at a greater intensity before experiencing symptoms.
 * Resistance training focusing on strengthening the muscles of the respiratory tract can also help when it comes to aerobic training.

The following is a summary of how asthma can respond to aerobic training with regards to the likelihood of provoking exercise induced asthma symptoms.

Suggested Readings
Sports Medicine Australia: Asthma Management

Asthma Foundation of New South Wales: Being Active with Asthma Fact Sheet

American College of Sports Medicine: Information on Exercise-Induced Asthma

National Asthma Council Australia