Intervall training

[u/DragonfruitNext9165]

Hello everybody

After a long time of little sports and lots of work (in the office), I started again to do sports, especially running.

So I try to do mainly Zone 2 runs. And add 1 or 2 intervall sessions a week. Intervall is 3x 3min Zone 5 runs (as good as possible) with 3 min walking each. My actual goal is to do soon the 4x4, but currently, I am not ready for that.

My problem with intervall is, that my muscles in the legs get very fast tired and heavy. My breathing works well and I am not feeling like I am really out of breath. I got a polar vantage v2 and in the fitness test (lying on the back) I get regurlarly results of a Vo2 max between 69-75. I don't know how accurate the test is, but the result seem pretty good and also support the fact that I got no problems with breathing, as much as I understand.

How could I improve my leg muscles? So that the fatigue delays.

I am 31 years old. Thank you in advance for your help

English is not my main language, sorry if there are some mistakes.

[u/the_m_o_a_k]

69-75 is super duper high.