Is it the "forced" part that yields results, or the simple fact that it was more exercise? The article said they were forced to go at a speed faster than what they were comfortable with, yet the rodent study had them forced to go slower than their natural pace, with better results. A follow up study forcing people to go slower than usual would be interesting.
I think it matters more if you are cognitively present for the exercise, rather than the intensity of the exercise. It doesn't matter if you go fast or slow, it only matters that you are doing something you're not used to and as a result actively think about it when you are doing it.
For example, writing with your left hand if you are right handed may be an equally effective method of achieving similar cognitive results.
One well worn piece of advice from health fitness trainers has always been to vary up your routine. I think this is the key to making sure you work out different muscle groups, but also a way to keep your mind engaged.
My hunch is that this is partially what's going on in the study.
I agree with the basic hypothesis. Though wonder how it can be measured. I know my preferred term is awareness, but neither is it any more measurable. My experience suggests two tasks at a time is a reasonable substitute to make sure you are aware. For ex: counting the steps while running
I agree. It probably invokes an element of awareness, that primal "oh, shit, I need to start working or else." It's probably that fear which provides certain types of endorphins and brain activity you wouldn't otherwise get.