That is a question I get from my patients quite often. And it is a loaded one. It really depends on why you are exercising. So, lets break it down:
If you absolutely hate exercising and only doing it because it is good for you or because your spouse is forcing you, then according to the American Heart Association and CDC guidelines, you need about 150 minutes of moderate or 75 minutes of vigorous exercise per week. If you enjoy exercising and are doing it for health and pleasure, then any amount past the minimum is good. Now, whether you get more benefit from any extra time is up for debate. There are no randomized controlled trials (the gold standard) with long enough follow up to measure meaningful outcomes from exercising more, but there does not appear to be any harm to it either. You may gain some extra cardiovascular benefit and lower blood pressure, but wether that translates into better long term health outcome is unknown. And of course the more you exercise the more calories you burn, so if weight loss is on your mind, keep going longer than the minimum.
Another important factor to keep in mind is that the guidelines do not require you to do all of your daily exercise at one time. For example, if you are doing moderate exercising 5 days a week, you need at least 30 minutes a day (for the math handicapped: 5x30 equals 150 minutes per week). The 30 minutes can be all at one time, could be three 10 minute intervals or two 15 minute intervals. So, two or three shorter runs in the day is as effective as one longer run. You got a big dog that needs exercise? Great, make those daily walks into short runs or brisk walks, good for and your pet.
Now, let's talk about what each type of exercise means and how you can achieve it. :
Moderate exercise: this is any activity that raises your heart rate "moderately." How do you know what is moderate? Well, you can buy a fancy watch, do some heart rate testing and establish your heart rate zones (see https://www.healthierlifemd.com/exercise for more details on heart rate zones). Or, more realistically and easily, you know you are in moderate exertion if :
1) You are slightly to moderately short of breath, you can hold a short conversation but only in a few words. If you are talking comfortably in full sentences, you are not working hard enough; if you can barely say a word you are working too much. And you don't need a partner to talk, perfectly normal to talk to yourself every few minutes! I do it all the time and am still not arrested as a lunatic.
2) You can do a simple count test: during your exercise count from 210 to 220. You should be able to say each number with a breath or two between. If you can count quickly then you are not pushing enough, if you can barely finish, back off. Do this every few minutes to make sure you are in the right zone.
If you have a smart watch with a heart rate monitor, look at your heart rate during these efforts. Your moderate pace for that particular exercise is around that heart rate, give or take 10 beats. But be aware that various exercises stress your body in different ways, so your heart rate may be different. My moderate exertion heart rate for running is in 130s, for biking its 120s and swimming it is 110s. The good news is that once you do this a few times you will get a hang of what it feels to be moderate and don't need to check anymore.
Vigorous exercise: Well, this one is much easier. You simply go hard. These exercises are mostly done with the now famous High Intensity Interval Training (HIIT). The idea is that you push as hard as you can for a short time, followed by a short rest, and then repeat. HIIT exercises stress your heart, lungs, muscles and joints more than moderate exercises. So, while you can do moderate exercise 5-7 days a week, you should limit your HIT exercises to 3 days a week and at least one day off between.
Which one is better?
There is really no large scale long term clinical studies to answer this question. In one small randomized observational study, overweight middle age men were randomized to moderate exercise 5 days a week versus vigorous exercise 3 days a week. After 8 weeks both groups had improved their metabolism and cardiovascular health. But the moderate group had more fat loss and lower blood pressure. In addition, all subjects reported better mood and less anxiety on days they exercised. So the mood benefit was 5 days for moderate exercisers and 3 days for vigorous exercisers. Now, this was a small study of middle age, out of shape men, so it may not apply to everyone, and the differences were very small. Other studies have failed to show any meaningful difference. But all studies have shown that exercising has health benefits.
This may be in contrast to some commercials you have seen with HIIT exercises: showing fit people sweating and promising rapid weight loss and a super model body with only 15 minutes of exercise 3 times a week. Well, that is Hollywood. In reality no amount of minimal exercise will get you a beach body UNLESS you also implement other changes in your lifestyle: that includes your food quality, sleep quality, psyche and activity throughout the day. So, don't choose your exercise type based on fake news.
What should you do?
You should do all of them. The best exercise is one that combines moderate and high intensity and includes some sort of whole body strength training. This could be as small as 30 minutes a day for 5 days a week or as long as you want it. You can do strenuous exercise 2-3 times a week with 2-3 days of moderate exercising between them. For example, on Monday do a 20 minute HIT regiment, on Tuesday do a 30 minute moderate jog, bike, or even do some yard work and so on. And always take 1-2 days off per week to allow your muscles and joints to recover.
As a recreational triathlete I exercise about 45-90 minutes a day 4 days a week and 2-3 hours a day 2 days a week with recovery on Mondays. I include both steady state moderate exercise and short high intensity intervals in my daily regiments. Exercising is my hobby, a way of meditation and socializing for me, so I truly enjoy it. Hence the excess time spent sweating. On other hand, my wife likes shorter exercises. She does 2-3 days of HIT that includes whole body strength exercises for 20 minutes interspersed with 2-3 days of moderate run or fast walks. Thanks to her better genes and eating habits she is thinner and has better blood tests than me: so more exercise does not necessarily mean better.
Let's finish with one last but very important fact: exercising does not give you the right to sit on your bottom the rest of the day. In fact the best benefit to your health is when you exercise AND stay active throughout the rest of the day. If you go for a jog and then spend the rest of your day inactive, you are still unhealthy. See https://www.healthierlifemd.com/staying-active on how to increase your daily activity by making small practical changes in your daily life. It's much easier than you think.
Ok, enough sitting and writing, time to go for a walk with my two little dogs. If you want to learn more all about healthy living come see us at HealthierlifeMD.
References:
CDC guidelines: https://www.cdc.gov/physicalactivity/basics/adults/index.htm
https://www.consumerreports.org/exercise-fitness/how-much-exercise-do-you-need-to-see-health-benefits/