GLOSSARY

Expiratory reserve volume (ERV) is the maximal extra volume of air that can be exhaled after a normal expiration with active, maximal effort; about 1–1.2 litres in a young man and about 0.7–0.8 litres in a woman.

Characteristics

• Muscles involved: the abdominal muscles and internal intercostals.
• Limiting factors: closure of small airways (especially in older adults) and chest wall stiffness.
• Dependence on position: ERV decreases when lying down, because the abdominal contents push the diaphragm upward.

During Exercise

• Using the ERV: during exercise, active expiration lowers end-expiratory volume and uses part of the ERV, helping to increase tidal volume and diaphragm efficiency.
• Difference in patients: in COPD, because of expiratory flow limitation, end-expiratory volume rises during exercise (dynamic hyperinflation), the opposite of healthy people.

Clinical Application

• Obesity: ERV is greatly reduced in obesity and may lead to airway closure at the lung bases and lower blood oxygen.
• Pregnancy: ERV falls by about 20 percent in late pregnancy.

Relevance to Sport

• Practical example: weight loss in obese people increases ERV and reduces exertional breathlessness, one of the respiratory benefits of reducing abdominal fat.