I do an 8 minute workout every day with an application. My workout is a mix of different excercises (hindu push-ups, abdominal etc, 30 seconds each). before this I used to do easier work-outs. I've been doing this workout for more than a month regularly, but it doesn't become easier. I am stuck at "comfortable" level and my heart rate after workout is 110-130 bpm. What am I doing wrong?
Insanity is doing the same thing over and over again but expecting different results
When you do the same workout every day without changing your intensity, the reps, the sets, or overall time worked out, then you are going to plateau and that workout will no longer be enough to grow your muscles.
Increase your workout's intensity gradually over time (extra reps, add weight). Your body will adapt to the extra load by building more muscle. This muscle then helps support an even larger load: rinse and repeat.
As an aside, there are two problems with your workout that also contribute to poor muscle growth.
Daily workouts constantly stress your muscles but never gives them time to recover and grow bigger. Reduce to 3-4 days a week so they can properly recover and grow.
Eight minute workouts are not very intense, so you aren't able to do enough to really grow muscles in that time. Increase to 30 - 60 minutes so you can properly stress your muscles enough.
Progress is easy, given you train regularly and have sufficient nutrition and rest. For a beginner. When you become advanced and your achievements much better then those of untrained people , you need to plan cycles , as progress is possible only in specific part of the body or one skill at a time.
When you become elite, ie world class sportsmen say olimpics, world championships, national level ....
At this stage your life is organized around one specific event (or say season).
Hardly you are an elite as in this case you would have a coach/trainer.
So i assume you are a novice.
In this case you could try to change one of 3 variables:
You train too hard too often. You do not get enough food to recover. You do not have enough sleep/rest to recover.
And there is a possibility that your training is not intencive enough to shift the homeostasis. 8 minutes look too short to me , however if you do Tabata protocol , for example it is even too much , especially every day.
Try to think of it and change one thing at a time , observe the results over 2 weeks period and then decide .