I am trying to understand something and i am hoping you guys can help me to explain it.
I started walking/running a week ago. 90 seconds of walking, then 60 seconds running for 45 mins.
At first i could only be able to run 7 times during that 45 mins workout. I was soooo terribly out of breath. But now at the end of the week i can complete the running part.
So my question is WHAT CHANGED? I noticed its all about breathing and being out of breath and that made it impossible to finish at first. But what changed at the end of the week with my breathing?

Why all of a sudden i am not out of breath so easy?

I'm no expert, but I'm guessing it's a combination of factors. You've probably improved your aerobic conditioning a little. You may have settled into a more efficient running style. And maybe you are just a little more "used" to that out of breath feeling so you tolerate it better.

That's the great part about beginning something new -- improvements come so rapidly!! You'll see amazing improvement just by working at it consistently.

Keep going!

Ditto on what MBN said. Also - are you running indoors or out? I find weather, tempurature, humidity all affect me = sometimes making it easier, sometimes harder.

Ditto to what MBN said. Good for you!!!

I run Indore. What exactly is improving inside though?

I think your body and lungs are just getting used to the exercise. When I started running, I was the same way, out of breath, and now, I don't get out of breath unless I really push myself. Eventually, you've gotta push yourself harder to feel that "out of breath" feeling. The fact that it takes you longer to feel that way is GREAT! Your body is adapting to your new lifestyle, thus making your workout a lot easier on you! Congrats! and Keep it up!

Humitidy and temp outside is still going to affect the tempurature and humidity inside. (I keep dreaming of spring... when I will be able to run outside again... if the snow ever melts. ~sigh~)

I started jogging years ago because I found it a very challenging thing to do - I never thought I would be able to run. But improvements came quickly. I think that is why I was able to stick with it. Being able to run/jog a little faster or a little further than last time is so rewarding.

Sometimes time of the month affects me... or what I have been eating. The healthier I eat, the faster I see improvements.

The learning curve, in my experiencem is fairly steep for running.... yoiur body us already geting udsed to it!

Are you folowing couch to 5K, or anythig like That?

From my personal experience...lung capacity adapt and increase very quickly. Each week, I could go further. That said, I just want to throw a little CAUTION to the wind...your lungs will adjust much more rapidly than your joints...so be careful not to advance too quickly. Ex...when I first started out, I'd stick with one level for 1 1/2 - 2 weeks before upping my running time/mileage...that gave my joints the time it needed and prevented injuries.

yes i am learning to get that stamina for running longer than 1 min lol
I found this 9 weeks training. I have done it before and actually was at week 3 a year ago... then now i have to do it all over again.

yes thank you! i am planing to stick for 2 weeks in the same level. Last time i did it i was already 20lbs lighter so i did 1 week level a week.
I stoped exercising and gained all of that plus 20Lbs... now I am promising myself not to quit. I will do 2 weeks of week 1 level for now.

YES YES YES

Just because you CAN does not mean you SHOULD. Yet.

New runners trying to force their muscles and bones to keep up with their cardiovascular progress is the oldest new runner injury in the book. And every new runner who ends up injured writes herself off as a one-off, just one of those things, and not someone who's either ignorantly (well-meaning-ly, but ignorantly) exceeded reality-based recommendations or who's been failed by an over-eager, too-fast-too-soon program.