Compare the heart rate at each consecutive pair of measurement points.<br><br>
0 to 5 km shows the steepest rise -- the heart rate jumps by the greatest amount in this interval.<br>
All other consecutive pairs (5-10, 10-15, 15-20, 20-25, 25-30, 30-40, 40-42 km) show smaller increases.<br><br>
Final Answer: 0 to 5