For most healthy adults, 150 minutes of moderate-intensity or 75 minutes of vigorous cardio per week is the evidence-based minimum, supplemented by strength training twice a week. Those who want to maintain weight after losing it likely need 225 to 420 minutes per week.
International guidelines are clear about the minimum amount: at least 150 minutes of moderate-intensity aerobic activity per week, or 75 minutes of vigorous aerobic activity. Moderate intensity means you can tell you are moving but can still hold a conversation, such as brisk walking or cycling. Vigorous intensity means you become noticeably out of breath, such as running or interval training. In addition to cardio, it is also recommended to train all major muscle groups with strength training at least twice a week. This is considered a safe, proven effective and achievable minimum for the general population.
The health benefits of this amount of physical activity are wide-ranging and well supported by evidence. Regular aerobic and muscle-strengthening activity reduces the risk of death from all causes, lowers the risk of various types of cancer, improves cardiovascular health, supports bone strength, improves metabolism and helps protect cognitive health. In short, few other lifestyle interventions have such a broadly proven effect.
If your goal is not only to stay healthy but also to maintain weight after a period of weight loss, 150 minutes is probably not enough. Research shows that 225 to 420 minutes of moderate-intensity activity per week is associated with better weight maintenance. Note: this is an association, not a proven causal relationship. It does point in a direction: more activity helps, but exactly how you achieve that is up to you.
For older adults, an addition to the basic guideline applies. A good exercise programme combines daily aerobic, strength, balance and flexibility exercises. That combination helps prevent falls, counteract muscle loss (sarcopenia), slow bone loss and limit cognitive decline. Unfortunately, most older adults do not reach the recommended minimum threshold, even though they stand to benefit from it the most.
Physical activity also carries risks. The musculoskeletal system, think muscles, tendons and joints, and the cardiovascular system can be negatively strained if you do too much too quickly. These risks are, however, well manageable with a gradual build-up, appropriate equipment and correct technique. People with a known heart condition or other medical condition are wise to consult a doctor before starting more intensive training.
Based on two broad guideline publications (PMID 33213121, 32984942), a review on physical activity in older adults (PMID 33010902) and a review on physical activity during pregnancy (PMID 23014142). Strong evidence for the basic guideline; moderate evidence for higher amounts in the context of weight maintenance and for specific subgroups.