Final answer:
An average athlete should train within the 50-75% intensity range of their maximum heart rate reserve to improve fitness effectively without overstraining. The maximum heart rate reserve is based on the formula 220 minus age and adjusted by the individual's resting heart rate.
Step-by-step explanation:
A training zone intensity of 50-75% of the maximum heart rate reserve should be used for an average athlete. This range ensures that the athlete is working out at a level that is effective for improving cardiovascular fitness without overstraining. The maximum heart rate reserve is calculated by subtracting the individual's resting heart rate from the maximum heart rate. Maximum heart rates (HR) can typically be estimated by the formula 220 minus the individual's age. Therefore, a 40-year-old might have an approximate maximum HR of 180 beats per minute (bpm). With exercise, cardiac output (CO) can increase up to 4-5 times the resting rate in healthy young individuals and even 7-8 times in top cardiovascular athletes.
Maintaining a heart rate within the recommended training zone allows the body to increase endurance and strength appropriately. It's also essential to note that heart rate targets may vary based on fitness levels, age, and overall health. Hence, athletes should consider individual factors when determining their specific training zone.