A performer takes part in a 30-minute training session. The table below shows the performer's heart rate at different stages. Stage Heart rate (beats per mi...

(a) The heart rate data shows a clear pattern:

• Heart rate increases during exercise, rising from 72 bpm at rest to 148 bpm after 10 minutes and further to 162 bpm after 20 minutes. This continuous rise reflects the growing demand on the cardiovascular system as exercise is sustained. [1 + 1]
• After exercise stops, heart rate gradually decreases back towards the resting level, dropping from 162 bpm to 110 bpm after 5 minutes and then to 78 bpm after 15 minutes (close to the original resting rate of 72 bpm). [1]

(b) The performer's heart rate does not return to resting level immediately after exercise because:

1. The body still needs to deliver extra oxygen to the muscles to repay the oxygen debt that built up during high-intensity work. [1]
2. Waste products such as lactic acid and carbon dioxide still need to be transported away from the muscles and processed, which requires continued elevated blood flow. [1]
3. The body needs time to return to homeostasis, restoring normal temperature, hormone levels, and metabolic rate. The gradual decline in heart rate reflects this recovery process. [1]