I can only attribute this to the new more vigorous treadmill routine... and possibly the punches and push ups? That is the only thing that changed.

I am intrigued by the heart rate monitors. I suspect I am underestimating my calories burned. But it is worth getting a monitor? It might make me exercise even more.

Now that I am pushing my body to adapt to a new routine... it is adapting! So I will have to keep pushing upwards and faster. But that will build muscle.