Answer Happy

please answer the following questions 1 and 3 short answer
and please label your answer to which question
1. In short terms, explain why endurance athletes require such a massive cardiac output. Think about the effect of exercise on muscle fibres and the circulatory system. **Max 200 characters.
3. To summarize, compare the cardiac output and resting heart rates of endurance athletes and an average adult and infer why such a massive difference might exist. Be sure to include a comparison to the heart structure of endurance athletes vs an average person! **Max 300 characters.