According to this study, using mental and emotional resources to solve problems or cope with issues at work decreases an individual’s ability to motivate themselves to exercise. According to the authors of the study, using willpower to address one task leaves you with less willpower to tackle other tasks. From the article:
"After we used this cognitive task to deplete participants' self-regulatory capacity, they didn't exercise as hard as participants who had not performed the task. The more people "dogged it" after the cognitive task, the more likely they were to skip their exercise sessions over the next 8 weeks. "You only have so much willpower."
The authors go on to note that using up cognitive resources is not an excuse to forego other healthy activities, such as exercise. Certain activities, such as listening to music, were reported to recharge one’s batteries, and making specific plans (like scheduling exercise every night at 7 pm) also counteracted this effect. Willpower was also compared to a muscle, in that the more one uses it and exercises it, the more it develops.
This seems to be a researched-based confirmation of what many people have intuitively observed. Many people struggle with maintaining a diet, working out as scheduled, etc. when they are coping with situational stressors, such as crap at work. In fact, the technical term for this concept in the research is ego depletion. I'm not too familiar with the various areas in which this issue has been researched, but I do think that many people have observed edo depletion in their own lives.
I personally have found that once in a groove, I am able to maintain a pattern of diet an exercise for a significant period of time. It’s only when I’m thrown off by some situational factor (such as travel) that the pattern gets disrupted. Of course, it may then take awhile to get back into that groove. I also wonder if people who exercise first thing in the morning have an advantage in this regard. That is, they get their workout in before any stressor can impact their day. As a clinician, I wonder to what extent ego depletion impacts therapeutic progress. First, is the therapy session itself less productive than it otherwise might be (and to what degree) due to the will power being used by clients just to get through their day? More generally, will clients have some difficulty applying what they've learned in therapy to their lives due to ego depletion? Certainy something a therapist should take into account...