It's called 'cognitive appraisal' and put simply, it means instead of focusing on the discomfort, channel your feeling towards focusing on the positives.
A good example of 'cognitive appraisal' is: if you didn't do well in a test, instead of dwelling on how poorly you did, take the opportunity to learn what you need to improve on.
Gathering a group of 24 healthy runners aged between 18 and 33, a team of researchers made them go through three rounds of "vigorous exercise." For the workout, they were required to a 90-minute treadmill run, with 75 to 85 per cent max heart rate.
However, before during and after each run, participants completed psychological tests to measure their emotional responses.
For the first run, joggers were asked to approach the exercise as they usually would. For the second and third round, runners were required to run with "cognitive appraisal" in mind - they were asked to detach themselves from feelings of struggle.
The findings showed that when they took on a "cognitive reappraisal" game plan, their "emotional arousal" levels were much lower than when told to run without instructions. The results found that this might be the trick to dealing with a tough workout if you're not up for it.