An experienced running coach has recently opined that spending an hour in the gym doing strength is about equivalent to 10 minutes of running.
Part of the reasoning could be the activation of different energy systems. Lifting activates the anaerobic system, whereas sustained cardio activates the aerobic system and dips into the anaerobic only at higher levels of effort. The anaerobic system transmits something like 30+ ATP (energy currency of the body), whereas aerobic is 2 ATP [1]. That might explain why you experience this difference.
Part of the reasoning could be the activation of different energy systems. Lifting activates the anaerobic system, whereas sustained cardio activates the aerobic system and dips into the anaerobic only at higher levels of effort. The anaerobic system transmits something like 30+ ATP (energy currency of the body), whereas aerobic is 2 ATP [1]. That might explain why you experience this difference.
[1] http://ksuweb.kennesaw.edu/~vking2/PhotosynthesisandCellular...