Every morning I do stretches and a kilometre jog. Also I do 100 pushups daily spread out in ten pushup blocks. I`m a 13 yr old girl who's height is 160cm and I weigh 57 kilos.I`ve been exercising like this for the past month and eating healthier too, though my weight hasn`t changed. Is it muscle or am I still not doing enough exercise?

It sounds like good exercise, though you could add some squats or burpees. What are you doing for the rest of the day?

I guess there will be as many opinions as there is people.

I would add to the push ups, if 10 at a time is easy, push it till it is no longer easy 10 is just a warm up and 20 to 30 is normal in our work outs. Add to that sit ups and some squats. Also toe touches. You need to try and get up to a 20 to 30 min work out routine that will raise your heart rate in addition to running.

Of course I am from the US and too lazy to look up what a kilometer is but what speed are you doing it in ? Is that speed increasing

It could be your diet, also as you grow (you're 13 you're not done growing), your weight will shift to new places. So you may be toning up and filling out. I would focus on eating well, it sounds like you're plenty active.