Which statement best describes tidal volume and breathing rate changes during increasing exercise intensity?

• A. Tidal volume is breaths per minute; breathing rate is amount of air per breath; both decrease with intensity
• B. Tidal volume is the amount of air per breath; breathing rate is breaths per minute; both increase linearly with intensity
• C. Tidal volume increases consistently with intensity; breathing rate remains constant
• D. Tidal volume increases at lower to moderate intensities and then plateaus, while breathing rate increases more at higher intensities

Answer: (D)

When exercise intensity rises, the body first increases the depth of breathing, so the amount of air moved with each breath (tidal volume) goes up. But the lungs and chest muscles have mechanical limits, so tidal volume tends to level off as effort becomes high. To keep meeting the greater oxygen demand and to remove more carbon dioxide, the body then relies more on increasing how fast you breathe—the breathing rate. So tidal volume climbs at light to moderate effort and then plateaus, while breathing rate climbs more at higher intensities. This is why the best description is that pattern. The other ideas mix up what tidal volume and breathing rate measure or how they change with intensity.