Final answer:
Irisin levels do indeed increase with aerobic training, a fact that has been confirmed by scientific research. This response clarifies that a positive correlation alone does not confirm health benefits, distinguishes between types of muscle tissue in the heart, and categorizes sprinting as an anaerobic exercise.
Step-by-step explanation:
Irisin is a hormone released during physical activity, and studies have shown that its levels rise following aerobic exercise. This increase in Irisin has been linked to various health benefits, such as improved metabolism and the browning of fat tissue. Regarding other statements you mentioned for clarification, a positive correlation does not inherently mean there are health benefits to the variable under investigation without additional context. It simply indicates that two variables move in the same direction. Also, the heart does not consist of smooth muscle tissue; it is composed of cardiac muscle tissue. Lastly, sprinting is generally considered an anaerobic exercise because it requires short bursts of high-intensity effort that do not primarily rely on oxygen for energy production.