Energy expenditure is proportional to aerobic activity. The type of exercise is not important; any activity where your aerobic capacity limits your speed (or rate) will be equivalent to any other. Strictly speaking, it is only these activities which are truly "aerobic". Running, bicycling, stair stepping, etc. are all equal, so long as you are exercising at your full aerobic capacity. Anaerobic exercises like lifting weights, sprinting, or bicycling up a sufficiently steep hill (i.e., at a low pedal rate where muscles begin to "burn") will be limited by your muscular strength/endurance, and thus involve less energy expenditure. Recovery from anaerobic exercise also involves energy expenditure, but this effect is not great enough in itself to compensate for the decrease in aerobic activity. "Interval training" or "HIIT" involves aerobic activity interspersed with anaerobic sprinting. There is reason to believe that, taking into account recovery expenditures, the right combination of the two types of exercise may allow for even greater total energy expenditure than pure aerobics however, not by very much. The purpose of interval training is usually not to maximize energy expenditure; it is more often used in athletic training. See the Activity Calorie Calculator to calculate approximately how many calories will be expended for 222 different types of exercise.