For healthy adults under 65 years of age:

The general physical activity recommendations outlined by ACSM (American College of Sports Medicine) and the AHA (American Heart Association) are:

Moderately intense exercise 30 minutes a day, five days a week
OR
Vigorously intense exercise exercise 20 minutes a day, three days a week
AND
8 - 10 strength training exercises, 8 - 12 repetitions of each exercise, two days a week

For adults over 65 years of age (or adults 50 - 64 with chronic diseases):

Moderately intense cardio exercise 30 minutes a day, five days a week
OR
Vigorously intense aerobic exercise 20 minutes a day, three days a week
AND
8 - 10 strength-training exercises, 10-15 repetitions of each exercise twice to three times per week
AND
If you are at risk of falling, perform balance exercises
AND
Have a physical activity plan*

*Older adults and adults with chronic conditions should consult with a health professional to determine an activity plan that is appropriate and safe.