To me discipline equals will power.
While not on HRT a dropped 50 lbs. with eating less but healthy, drinking less but better drinks, 2x a week 3 miles jogging, 2x a week jumprope for 20 minutes.
As you age the optimal heart rate beat for burning fat is dropping so you have to monitor your hear rate in order to exercise most efficiently. YOu can find chart for your age group somewhere online or buy one of those watches that mesure hear rate, They usually come with that chart. Important thing to keep in mind is that the fat burning process doesn't start until about after 20 minutes into the exercise. So you don't want to overdo it right away and quit after 30 minutes as that means you only had about 10 mintes of effective fat burning exercise. It will also take you some time to gain the condition to exercise for 45 minutes or more. Take yourself a time just try to be steady and committed. It took me 1 year to loose my weight.