Respiratory rate increases with exercise intensity

Steps:

• Identify pattern before X as steady, slower volume oscillations indicating moderate activity like walking.
• Note change between X and Y to faster, deeper oscillations reflecting heightened breathing.
• Link this to physiological response: exercise boosts oxygen demand, accelerating respiratory rate.
• Conclude cause as transition to more intense activity matching the pattern shift.

Why B is correct:

• Running elevates metabolic rate, increasing respiratory frequency per Fick's law of diffusion to meet higher O2/CO2 exchange needs.

Why the others are wrong:

• A: Switching to walking reduces intensity, slowing respiratory rate opposite the observed acceleration.
• C: Internal intercostal muscles aid forced expiration; decreased frequency would prolong breaths, not accelerate them.
• D: Decreased contraction strength reduces tidal volume amplitude, not oscillation frequency.

Final answer: B