The most effective strategy I have come across is to "change your identity". If you identify as an athlete, and you talk to yourself and others with that expectation, then that is much more effective than "I need to get in better shape".
When you identify with something it compels your actions, almost by default, much more than willpower alone.
So in your given example, another way of referring to what you are doing is to say that you are adopting the jikaku of an athlete. In a sense, adopting the role of athlete is more effective because it is ascribing both an outer and inner identity element to yourself.
Perhaps you will be curious. I found it to be an interesting overlap with what you've discovered on your own.
Conversely, if I focus on the 2 mile mark (for example) and glance at the meter to see that I've only traveled 0.6 miles, it's quite frustrating. Each successive glance shows a marginal increase towards the goal, adding to fatigue. Better not to watch the clock at all.
"however...the greater use of these two effective strategies did not explain why these high trait self-control individuals tended to enjoy greater success at aversive challenges"
So, in fact, this study identified which strategies were effective in people who were (self-reportedly) already effective at handling aversive tasks.
What I find surprising is the lack of mindfulness on the list, i.e. employing mindful awareness to an activity as a way to deal with it.
Mindfulness to me would be just To continually bring awareness to whatever I feel, sense, think, without connection to a process.
If there are averse conditions, running away from what we feel is the opposite of mindfulness and any directed way of distracting/framing the situation would be going away from mindful appreciation of the very aversive situation.
The premise being that a lot of stress is produced by the mental process of prediction and thinking into the future or the past, and by redirecting attention the the areas where you are taking immediate action, you produce emotional reactions to the sensation of progress, instead of emotionally predicting the potential outcomes of the hypothetical future.
Note that this applies even if you are resting or relaxing — “all I have to do now is breathe”.
You could also focus on emotions and thoughts i e Just notice wgat you feel or think without trying to change it.
At an even deeper level, it ignores the deep motivations that drive people. Especially for people who are low in conscientiousness like myself, they need a deep existential reason for pursuing their goals. Merely setting up a goal I think I want and then working toward it isn't sufficient to drive me.
It has to be tied to a sense of meaningfulness toward my life (e.g. I'm not depressed or nihilistic), actively policing my negative self-talk, questioning my sense of paranoia or bad intentions in others, feelings of gratitude, etc.
I find if these drivers of my behavior/psychology are fixed, the other stuff just "snaps" into place.