People who love to lift typically don’t look forward to cardio day. That’s also the trend among runners and cyclists on the days they set aside for strength training. A study from the University of Utah looks into this separation of performance traits using lab mice.
 

Researchers observed how effectively some mice protected their territory by fighting off other mice. They also measured the running efficiency of mice using a treadmill.

Rodents that were successful fighters burned more oxygen while running compared to less successful fighters. Although there weren’t significant differences in body mass between runners and fighters, scientists theorized there might be small physiological differences.