Final answer:
Heart rate monitoring is the method that correlates directly to 60 - 80% of VO2max, as it provides an objective measure that can be directly compared to VO2max levels.
Step-by-step explanation:
The method of determining exercise intensity that correlates directly to 60 - 80% of VO2max is heart rate monitoring. Rate of perceived exertion (RPE) and scales like the Borg scale, while useful, correlate in a more subjective manner and are less direct in measuring exercise intensity in relation to VO2max. The use of Metabolic Equivalent Tasks (METs) also provides a measure of exercise intensity but is more of an estimation compared to direct heart rate monitoring.
Heart rate monitoring is a quantifiable and objective method that can be directly compared to VO2max, especially since certain heart rate ranges are known to correspond with specific percentages of an individual's VO2max. For instance, aerobic exercises increase heart efficiency and are often prescribed within a target heart rate range based on the individual's age to ensure cardiovascular health and efficiency benefits.