Final answer:
ISSA recommends training at 70-80% of the maximum heart rate for aerobic exercise, based on the estimate of maximum HR being 220 minus an individual's age.
Step-by-step explanation:
For aerobic training, ISSA recommends that individuals train at a heart rate of 70-80% of their maximum heart rate. The maximum heart rate (HR) is often estimated using the formula 220 minus the age of the individual. Therefore, a 40-year-old would have an estimated maximum HR of 180 beats per minute (bpm), while a 60-year-old would have a maximum HR of around 160 bpm. When training for aerobic exercise, staying within 70-80% of the maximal HR ensures an optimal intensity that is thought to improve cardiovascular fitness without the risks that may come with very high intensity, close to the maximal HR.