40 minutes is 10 km, 30 days for 10 km = 300 km and this is a marathon in 2 hours 50 minutes - more than worthy for an amateur. And 20-30 minutes - well, if you run for 3 minutes 30 seconds per 1 km, then probably the 3rd discharge at 800-1000-1500 will be at least.
Of course useful. At least some kind of physical activity is better than no physical activity.
If you are still a beginner in running, then in any case the first few weeks you will get used to the new load, run 10- 15-20 minutes, no more. Gradually move to 20-30 minutes, and this is quite an adequate load.
If you want to lose weight, then, of course, it is better to run for more than 40 minutes. It is believed that from about the twentieth minute, the body begins to “burn” its own fat reserves. But in any case, even with a 20-30 minute run you will burn a certain amount of calories , supplement this with the right nutrition, and the weight will begin to decrease.
If you just want to lead yourself in shape, you do not have any special problems with weight, then half an hour of jogging will be enough to make muscles more toned and elastic , improve the work of the respiratory and cardiovascular systems.
In addition In addition, running can be made more difficult , for example, running on rough terrain or uphill, doing interval races with a change of pace.
There is also the option that you "get involved", get carried away with running and want to run longer, and when there is a desire to do something, then there will be time)
It is believed that the effectiveness of aerobic exercise starts from 40 minutes, but at the same time, if you choose: to run for 20-30 minutes or not to run at all, then the first option is much more useful than the second. Because your body is still included in the work and fixes it. When it’s time to do longer workouts, it’s much easier to jump into them.
The meaning is there. But if you start with 20-30 minutes, then after a while you will want more.
20-30 minutes a day is primarily a boost of vivacity for the whole day, unless of course you train to failure. Approximately, after this very time after the start of jogging, the body begins to break down fats more efficiently - therefore, jogging for 40 minutes is recommended for weight loss.
Just control your pace - you should be able to talk easily on the run without holding your breath. Or control your heart rate - about 65-70% of your maximum heart rate (220 minus your age). Also, jogging in this mode develops the stroke volume of the heart and the capillary network in the muscles. After a certain time, your pulse and blood pressure will decrease, you will feel much better, and you will be able to run faster at the same heart rate.
You can run every day if you do not feel tired. But usually for beginners 3-4 times a week is enough. Athletes train 6 days a week. A minimum of 1 day of rest per week is necessary if there are heavy loads. On this day, it is useful to do a massage, visit a sauna.