At my apex, two years ago, I used to run approximately 7 miles everyday on the treadmill in about 70 minutes, I burned 1000+ calories, and I weighed approximate

At my apex, two years ago, I used to run approximately 7 miles everyday on the treadmill in about 70 minutes, I burned 1000+ calories, and I weighed approximately 220 lbs and I am 6 feet tall. When I first started using the treadmill, it was to lose weight, my starting weight was well over 300lbs. Currently I have a vaccine side-effect that I can't quite shake, so now I can't run for any appreciable amount; but I still manage to burn about 800 calories on the treadmill mainly by walking at an incline and some short bursts of jogging, throughout I have to rest, where I didn't previously. To answer your question: When I was still employed I ran nearly 7 miles a day in 70 minutes one day a week before work -- on an empty stomach -- and because I was intermittent fasting I didn't eat until late in the afternoon. I had a very physical job at an Amazon fulfillment center (warehouse), but I was still able to work throughout the day, without tiring. Albeit, I couldn't imagine, and never attempted to work at Amazon, and then running 7 miles after work. I was never injured to the point where I couldn't exercise, my joints held up well. When I first started using the treadmill, it was unfathomable to me to even walk one mile on it, I increased my pace everyday, and thus, I was able to build, overtime, quite a bit of endurance, my key was persistence.