Running fast but low heart rate?

I have worked my way back up to running 12 km in 70 minutes after having a baby 5 months ago. I didnt run much during pregnancy. At first when I started back, my heart rate rocketed.

My question is; although I am happy my running is progressing, when I push myself to run fast (on treadmill), and it feels tough, my heart rate is still very low for the effort? ie. at the bottom end of my training zone - 135-150 bpm) when it feels like Im doing 80 plus percent!?

Surely this is not just improved fitness, as I still feel Im pushing it. (My heart rate monitor is quite new)

Thanks for any feedback

Running fast but low heart rate?

If 150 bpm is near the bottom of your target zone then what is the top? I would seriously question the calculations you used for your target zone. What is your average resting heart rate?

If you%26#039;re running 12k in 70 min 5 months after having a baby I would say be happy about that and ditch the heart rate monitor.

Running fast but low heart rate?

u got it wrong the fitter u get the slower the heart pumps as ur body isnt been pushed the way it used to it is uded to the things ur doing wiv it try pushing urself harder but id be happy wiv a slow heart rate while exercising means ur v fit

Running fast but low heart rate?

The fitter you get the stronger your heart becomes, the lower your heart rate will be under stress, and the quicker your recovery period will be. You can always do a quick check against your heart monitor by taking your pulse reading, but dont forget, your pulse rate is varying all the time, even at rest.