As said before any exercise is good for you even if it's just playing tennis or basketball once in a while. Even a good long occasional brisk walk will do you good. A brisk walk gets the heart going and is something to enjoy when you see the scenery and walk with others. Similar activity is tending to your garden and mowing the lawn.
It's when we start exercising regularly that we start to get important health benefits. That is what the CDC says. For adults you need to do moderate activity which includes brisk walking for 2 hours and 30 minutes per week. This works out at 30 minutes per day from Monday to Friday. You can even divide the activity into 10 minute blocks.
For jogging and running you don't need to do it so long for the "important health benefits". You only need to go for 1 hour and 15 minutes, this works out at 15 minutes per day 5 days a week. Through the above link they give you some activities that are included for moderate and those for vigorous like jogging and running. Pick one you enjoy and take part.
If you're willing to exercise more
The CDC says there are "even greater health benefits" if you double those numbers. So 5 hours of moderate exercise or 2 hours and 30 minutes of vigorous exercise per week. This is a lot but doable and only entails running for 30 minutes per day 5 days a week. This is what I'm starting to do and I feel great. It does require commitment and routine.
Combined with all the aerobic exercise recommended by the CDC they also recommend that you do weight baring exercise on 2 or more days a week. The CDC is very demanding when it comes to the exercise they say we need. We have a page on strength training if you have access to a gym or weights but there are other activities they consider weight baring that may be easier to come by for many.
Treadmill running compared to outside
When it comes to exercise to what the CDC describes there is no difference to running outside or on a treadmill. You are exerting nearly exactly the same effort except with one you're doing it on the spot. If you want to make treadmill running the same as outside when it comes to the energy cost then the science says run on a 1% incline.
The problem is, and why people think treadmill running is that different, is because people that run outside and run races look down on people who run on treadmills. It's like they are a second class citizen and you can't be getting the same benefit by running on a treadmill. Well the fact is you can and do. It's just another way of getting exercise like rowing indoors compared to on a river or using an elliptical compared to cross country skiing.
Treadmill running routines
Perhaps you've heard of the boredom of treadmill running. You may have heard some scare stories of people moaning about running and getting no where. Some variation on the treadmill might help ease any boredom you're feeling. We have all kinds of routines including speed work which is great for outdoor runners as it improves your speed. It makes you run faster outside.
Often home treadmills will have workout programs you can call upon. They're often called "hill climb" or "calorie burn" and present a challenge and some variety. You could train for a race distance on a treadmill like the 5k, 10k, half marathon and full marathon. All of those take weeks to build up and gives you something to aim for on a treadmill.
Here are those treadmill speed workouts and they're something it's really worth trying if you have a personal best at any distance you're struggling to beat. The high intensity interval training (HIIT) one is a real challenge:
So as long as you're exercising it's good for you. Don't be persuaded as to which equipment is better than any other. If your heart rate is speeding up and your breathing has got more rapid and harder then you're doing yourself good. So treadmill running or not it's all good. A treadmill helps because you can easily see your time and distance on your console.
If you're finding the treadmill boring do check out the above routines for some variety. If you can do them regularly then you'll be doing what the CDC says for important health benefits. That's why treadmill running is good for you and just as good as running outside. If you prefer running outside then do it but don't neglect the treadmill totally as it may come in use when the weather is bad.