Final answer:
Until ACSM's 1998 position stand, the primary basis for establishing intensity was the Heart Rate Reserve (HRR). The HRR method calculates exercise intensity tailored to an individual's resting and maximum heart rate, with the Rate of Perceived Exertion (RPE) acknowledged by the CDC as an important subjective measure.
Step-by-step explanation:
The primary basis for establishing intensity until the American College of Sports Medicine's (ACSM) 1998 position stand was Heart Rate Reserve (HRR). HRR takes into account the difference between a person's resting heart rate (RHR) and their maximum heart rate (MHR) to calculate the Target Heart Rate (THR) during exercise. This method allows for individualized exercise intensities, which is essential because heart rates vary with exercise, fitness levels, age, and other factors, such as the influence of medication on heart rate measurements.
The Centers for Disease Control (CDC) also recognize the importance of personal perceptions in assessing physical exertion, recommending the Rate of Perceived Exertion (RPE) as a subjective measure of intensity. The RPE scale provides a more complete view of an individual's effort level during physical activities. This is especially useful when heart rate readings may be less reliable due to external factors.