I went for a run today and it was deeply painful. it was how running used to be when I was 2 stones heavier. It took effort to get out of the door, I ached on the way round and I resented nearly every minute.
This was not because I haven't run for a while, but because I have put on weight (about half a stone) over Christmas.
It reminded me that Bloom's exercise programmes must deal with diet as a mediator of persistence, as much as what is happening in your mind. In other words, if you are eating better and are lighter, you are more likely to exercise. Mind you, once you exercise it is easier to eat better.
The only thing that works in my experience are diets that replace carbs with protein (think Atkins) and the GI diet. Of these, the GI diet is by far the best, in my opinion.
The run round the block has many things standing in its way; but diet is the biggest. The challenge is to start replacing high GI food with low GI food in your weekly shop. 5 items at a time, replace them all.